The sill panel on a car is attached to the door pillar
and floor, and is of double-panel box-like construction
having both inner and outer panels. Because of
its position it is one of the most likely places to
receive damage.
Two methods of repair can be used for doublepanel
assemblies. First, cut away part of the inner
panel, or in the case of the sill, along the top. Then
bend the panel or top section upwards to make the
outer panel accessible for the use of hand tools.
Push out the damage using the spread ram which
acts as a wedge, or force it out using body spoons
as levers, then planish and file. Bend the top section
or back panel back into position and weld.
Care should be taken here to avoid overheating the
repaired area.
The second method, which is less time consuming,
can be used if the dent is small and not very
deep. The area can be sanded clean to bare metal
and filled using body solder. If the damage is very
deep it will need pulling out, and this can best be
done using a panel puller on the outer panel surface.
The holes needed for using this tool should
then be welded up and the damaged area should be
sanded, filled with body solder and filed to achieve
the final finish.
Minor repair of body panels
Using adhesives
With the advancement of adhesive technology,
Permabond have developed an adhesive specially
formulated for car repair applications and called
Autobond. This is a two-part product which has
been developed to meet the specific requirements
of the car repairer. It is designed to replace panel
welding with a minimum of surface preparation; it
will also protect against corrosion. It provides substantial
labour saving in avoiding the necessity to
remove fuel tanks and soft trim as required before
any welding repair. The adhesive not only bonds
metal to metal but is also suitable for bonding GRP
components.
For ease of use the adhesive is supplied as a
layer of resin on top of a layer of hardener inside
a plastic tub; the two layers will not react until
mixed with the stick provided. The resin and
hardener are coloured light grey and black respectively
to provide a visual check that thorough
mixing is achieved. After mixing is complete, setting
begins at a rate depending on the ambient
temperature. The best performance is achieved
by heating the bond area to 40 C for 1 hour;
however, at 60 C full hardening is achieved in
30 minutes. Curing at normal ambient temperature
will give joints of reduced strength and is not
recommended. Figure 13.67af shows the application
sequence.
Removal and replacement of
Exterior and interior soft trim
And hard trim
Body exterior mouldings are attached by weld
stud retaining plastic clips; weld stud retaining
plastic clips with attaching screws; an adhesive
bond using either tape or sealant; a self-retaining
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spring clip or clinch-type clip; or special attaching
screws.
During repairs, observe the following:
1 Adjacent paint surfaces need protecting with
masking tape to help prevent any possible
damage.
2 Always use the correct tools for the job, and
take great care with mouldings.
3 Water can leak into the interior of the body
through any body panel holes made by screws,
bolts and clips unless they are securely sealed.
Door trim
The door trim pieces are normally assembled in
one-piece or two-piece trim pads. Removal of
door trims is carried out in the following order:
door lock handle and door locking knob; mouldings;
window regulator handle and door latch
handle; arm rest assembly; mirror remote control
bezel nut; and door trim retaining screws (if any).
Then lift the trim panel retaining clips from the
door inner panel, and disconnect all wiring so
that the trim panel may be removed. Prior to
reinstallation of the trim pad, always make certain
that the watershield is in position and correctly
sealed.
388 Repair of Vehicle Bodies
(a)
(b)
(c)
(d)
Craft techniques and minor accident damage 389
(e)
(f)
(g)
Figure 13.64 Pull pin kit used with a spot welding gun (ARO Welding Ltd). (a) Clean the damaged area
with an abrasive disc. (b), (c) Set the spot welding gun controls. In case of doubt, perform a trial weld on a
section similar to the dented one to help you select the best setting.Weld the pins at the selected positions
on the damaged section. (d) Once the pins have been welded to the section, use the inertia weight tool to
pull the dented section back into its proper shape. (e) Make sure you do not exercise more pull than is
needed to bring the panel back into its correct position, to avoid bulging. (f) Use your normal shearing tool
to cut off the projecting portion of the pins. (g) For a smooth finish, go over the area with an abrasive disc
in the usual way
390 Repair of Vehicle Bodies
Figure 13.65 Fastening ring washers to the damaged
area ready to pull (Stanners Ltd)
Figure 13.66 Pulling damage out using hook
and slide hammer (Stanners Ltd)
Quarter trim panel
This is the panel which fits over the interior of the
quarter panel. Removal of the quarter trim panel is
carried out in the following order: rear seat cushion;
rear seat back; rear window handle (if any); and any
screws or mouldings. Then unfasten the panel
retaining clips and pull the trim panel away from
the quarter panel.
Floor carpet
Carpet for car floors is made either in one piece
which is moulded to fit the shape of the floor, or in
two pieces to fit the front and rear sections of the
floor respectively. In order to remove the one-piece
carpet it is necessary to remove everything in the
way, including seatbelts, seats, centre console, and
door sill scuff plates. However, the two-piece
carpet can be removed with the seats still in place
because they are made with cut-outs to allow for
easier removal. In some cases the floor of a car
is covered with heavy rubber flooring instead of
carpet, and this can be removed and replaced in a
similar manner.
Headlinings
Headlinings are of two types. The first is soft and
made from cloth or vinyl coated. The second is
harder, being formed from moulded hardboard
coated with foam or cloth which has a vinyl facing.
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The replacement of the moulded headlining
is a simple, straightforward operation because of
its one-piece rigid structure. The soft type is
more complicated in its removal owing to the
necessity of removing a large amount of trim in
addition to the windscreen and rear window in
some cases.
13.17 Aluminium panel repair
Differences
The repair of aluminium panels and other components
is slightly different to repairing steel ones.
Aluminium panel repair is not difficult; it is just
different to repairing steel ones. Not greatly different,
just that you should follow a set of procedures
and remember the characteristics of aluminium.
More and more vehicles are using aluminium
every year, more correctly we should say aluminium
alloy. Let us have a look at the characteristics
of the material, particularly its advantage
over steel.
Aluminium is light in weight, strength for
strength it is about a third of the weight. In an accident,
it will absorb double the energy of a similar
steel component. Given the correct environment it
does not corrode. It is a very abundant material and
easy to recycle. Because aluminium is easier to
work than steel, and it can be worked in different
ways, aluminium bodies can be made for a lesser
number of parts than steel ones. The big environmental
advantage is that by reducing the weight of
the vehicle the fuel efficiency is increased; a 10%
weight reduction typically gives an 8% reduction
in fuel usage.
(a)
(c)
(e)
(b)
(d)
(f)
Figure 13.67 Minor panel repair using adhesive; (a) preparing surfaces (b) cleaning with solvent (c) applying
adhesive (d) assembling joint with rivets, tack welds or clamps as appropriate (e) removing excess adhesive,
heating bond area, buffing joint (f) completed panel (Permabond Adhesives Ltd)
392 Repair of Vehicle Bodies
Figure 13.68 Audi A8 Aluminium body (Courtesy of POWER-TEC )
Galvanic corrosion
Aluminium is the fifth least noble metal, it is
almost at the end of the anodecathode scale, and
it has an anodic index of 0.95. This means that
whenever steel and aluminium come into contact
there is likely hood that galvanic corrosion is going
to take place. If there is dampness of any kind, such
as when rubbing down or cleaning, then some form
of corrosion is bound to take place. Although this
might appear insignificant at first, the smallest pin
prick of corrosion can lead to a large rust patch.
The smallest corrosion bubble will look unsightly
if it is in the centre of the bonnet or other highly
visible panel.
Steel particles from tools and abrasives can cause
corrosion to aluminium, so careful consideration
must be given to every possibility of cross contamination
between tools and panels to prevent corrosion
taking place.
Contamination
Repairers specializing in working with aluminium
bodied vehicles, such as Audi (Figure 13.68),
Jaguar (Figure 13.69) and Aston Martin use specialist
enclosed work booths for those vehicles.
That is, a booth which is fully enclosed and heated
and ventilated separately from the rest of the workshop
(see Figure 13.70). Also the tools and equipment
are dedicated for use only on aluminium
bodied cars. The tools used, where possible, have
non-ferrous working faces. That is, tools made
from plastics materials, or plastics coated tools, are
used where possible.
However, this is not usually practical for the smaller
repairer, or the general accident repairer. In which
case the following is advised:
Position the aluminium bodied vehicle in the
workshop so that it is quite separate from steel
bodied ones, especially when welding, sanding,
grinding or other intensive repair procedures are
being carried out.
To avoid cross contamination by minute steel
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particles from steel bodies to aluminium ones
use a set of tools for aluminium use only. That
is, you should dedicate a new set of tools for aluminium
repair use only. Colour code the tools by
painting, or plastic dipping their handles.
Keep the tools for use with aluminium bodies in
an enclosed tool box separate from those used on
other vehicles.
If possible, dedicate sanding and grinding
tools for use only on aluminium bodied cars.
Use the same colour coding system and store
them separately under covers. If this is not
possible, then clean the equipment with solvent
before use on aluminium bodies and use
new discs or abrasives to ensure that there is
no cross contamination.
Always wear a clean set of overalls and gloves
when working on aluminium bodies cars.
Always use new wipers and cloths when carrying
out aluminium repairs.
Craft techniques and minor accident damage 393
Figure 13.69 Aluminium bodied Jaguar (Courtesy of POWER-TEC )
Figure 13.70 Enclosed work booth for aluminium repair (Courtesy of POWER-TEC )
394 Repair of Vehicle Bodies
Riveting
When drilling out steel rivets from aluminium
panels be sure to collect any steel chipping to
prevent contamination and possible corrosion.
Punches are available to remove old rivets.
When replacing rivets be sure to use the correct
type. Often coated rivets are used to reduce the
risk of galvanic corrosion. The coating is usually
anodizing giving an identifiable colour.
Rivets are best applied with a rivet gun, however
copper rivets can sometimes be used and closed
using snaps which are hit with a hammer.
Oxidation
Oxidation on aluminium panels is invisible to
the naked eye except as there may be a slight dulling
of colour. As the oxidation layer will be over the
whole panel, the dulling will not be distinguishable.
A coating of oxidation is formed within a period of
two hours even in a well heated dry workshop.
Therefore a primer coat should be applied within
two hour of sanding or other preparation.
If the aluminium panel is left for a long period in
damp conditions, then the oxidation will become
visible as a coating of white powdery aluminium
oxide. Aluminium oxide (Al2O3) is both infusible,
difficult to melt without very high temperatures,
and amphoteric can form a base or acid which
implies it can be dissolved in caustic soda. Be
careful when using caustic soda as a cleaner,
always wear rubber gloves, goggles and apron as
the minimum PPE.
Immediately before welding aluminium panels the
areas to be welded must be de-oxidised clean the
best technique is to use a stainless steel wire brush
which as been dedicated for use only on aluminium
panel work.
Heating aluminium
Most aluminium body panels are hardened and
tempered for strength and dent resistance. The
aluminium will work harden on impact. Therefore
if the panel is dented the damage will be firmly
set in place. It will be necessary to heat the panel
to soften it to remove the dent and bring the panel
back into shape and contour.
Aluminium is a very good conductor of heat, so
spot heating is difficult. That is, the whole panel
becomes hot very quickly, as does the surrounding
area.
Aluminium fuses (melts) at about 650 C; but
the aluminium oxide will not burn off at less than
1250 C. Therefore it is important to clean off
the oxide prior to welding, to be able to keep the
aluminium fluid during the welding process at
650 C.
When heating the panel to carry out a repair the
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temperature should not exceed 200 C. This is the
threshold temperature for the aluminium. A usual
temperature range for the repair of panels is
between 110 C and 160 C. It is advisable to keep
the temperature below 160 C.
Special attention must be given to adhesively
fixed or bonded areas. Whether it is the panel
which is being repaired which is bonded or the
bonding on an adjacent panel or nearby supporting
member. Heat maybe applied to help disassemble
an adhesively secured or bonded joint; but be careful
not to apply any heat to a joint which should
be kept intact. Always pay special attention to
these areas both in terms of accidentally applying
direct heat or allowing heat to be conducted to
reach them. The use of heat soaks in the form of
damp material is one way of doing this; but make
sure that this is clean and thoroughly dried off
afterwards to ensure that no corrosion can occur
later.
Heat application
Aluminium panels can be heated in the same way as
any other panel; but the working temperatures are
very low compared to steel. Heat sources are:
Oxy/acetylene torch be careful with the flame
to ensure even temperature distribution
Gas blow torch use a low to moderate setting
(Figure 13.71)
Hot air gun probably the best method, especially
if it has a temperature control
Temperature measurement
Aluminium does not change colour or otherwise
give an indication of its temperature as it gets hot.
That is, until it suddenly melts.
There are several ways of measuring the temperature,
the choice depends on personal preference and
required accuracy. The more accurate the better,
Craft techniques and minor accident damage 395
(b)
Figure 13.71 (a) Heating the panel with propane gas (b) Conventional bumping file being used to raise dent
(c) Using a panel file (d) Threaded studs and loops for pulling repair from outside (e) High density nylon
compound panel hammer (Courtesy of POWER-TEC )
(a)
(c)
(d)
(e)
396 Repair of Vehicle Bodies
especially when dealing with vehicle with large
numbers of bonded joints.
Infrared or laser, point and shoot digital thermometer
These are very accurate, being able
to measure to a fraction of a degree. They
allow quick measurement not only of the area
which is being worked on, but any other areas,
for example adjacent bonded joints which must
be kept cool. The readings are instantaneous.
(Figure 13.72)
crayon and the speed is that of the chemical
colour change. These are limited too in that it is
not possible to track heat travel to adjacent panels.
Dent repair
Clean the whole area with soap and water to remove
any road dirt then dry off the panel. Remove the
paint coating using 80-grit or finer abrasive. Use
only a light pressure when sanding, especially on the
bare metal.
Wipe the panel with wax and grease remover
and dry off with lint free cloth or a wiper. Allow
any vapours to evaporate.
Warm the area to be repaired, checking that the
temperature does not exceed 160 C. Also check that
adjacent areas, especially where there are bonded
joints, are not getting too warm. Use an accurate
thermometer for this, dont guess.
Work the damaged metal using conventional
straightening techniques, keeping in mind how soft
the aluminium panel is compared to steel.
Use the tools which have been dedicated for use
only with aluminium bodies. Make sure that any
metal tools such as hammers, dollies and spoons
have smooth edges to avoid gouging the aluminium
panel. Pick hammers are likely to be unsuitable
because they are too sharp. The use of wooden
bossing hammers and purpose-made high density
nylon hammers are recommended.
Remember to re-heat the panel continually
throughout the repair process.
Miracle repairs
Lifting and repairing damaged panels from the outside
without removing interior trim or on otherwise
blind sections can be done using Miracle tools
(Figure 13.73). The system uses treaded studs and a
range of rings, pulling loops or collars and pulling
tools. The stud is welded to the damaged area of the
panel after appropriate removal of the paint coating.
A suitable pulling loop or collar is screwed onto the
stud. The panel is heated up if needed and the
pulling tool applied to pull the dent out.
When the dent is out the stud can be snipped off
(Figure 13.74), and then its remains filed or ground
down level with the surrounding area. Check for
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low and high spots using a panel file taking care
not to remove too much metal. Aluminium clogs
files, so keep the file clean using a stainless steel or
brass wire brush.
Figure 13.72 Laser point and shoot digital
thermometer (Courtesy of POWER-TEC )
Digital thermometer strips These are placed on
the panel, their plastic backing strip holding them
to the panel and allowing reading to be observed
whilst work is taking place. The readings take
several seconds to change, as the material
changes colour with the change in temperature to
indicate the temperature. Several of these may be
needed at any one time, and it may not be possible
to secure them to bonded frame areas if
there is not a suitable smooth surface. Accuracy
is limited to the pre-set limits of the strip.
Colour crayon The area to be heated is given an
outline mark with a crayon which changes colour
at a given temperature. With crayons the correct
one must be chosen for the job, the accuracy
is limited to pre-determined constituents of the
Applying a guide coat then using a long sanding
block, as is used for filler, high spots can be identified
without removing metal.
Heat shrinking
Applying heat to any dent, without any kind of
manipulation, may reduce the size of the dent due
to the thermal expansion of the aluminium.
Heat shrinking may also be used with hammer and
dolly to manipulate the panel and reduce the dent.
Cutting aluminium
Aluminium, though it is soft, requires special
care when cutting. The following points should
be observed:
Always ensure that the panel is fully supported
on both sides. If it is not, it may sag and bend
causing damage.
Use a reciprocating saw, such as an electric
jig saw.
Use a fairly course blade, Forrest Blades aluminium
saws have alternate six and four sided
teeth. Cutting fluid must be used with this tooth
shape.
Craft techniques and minor accident damage 397
Figure 13.73 MIRACLE pulling tool (Courtesy of
POWER-TEC )
Figure 13.74 Snip-off the studs (Courtesy of
POWER-TEC )
Figure 13.75 Control box to convert conventional MIG
welder to weld aluminium (Courtesy of POWER-TEC )
WWW.forrestblades.com
Use the correct cutting speed, up to 5.5 m/s (1000
feet per minute) much faster than for steel.
Aluminium welding
MIG and TIG are the normal welding processes
for use with aluminium. Follow normal procedures
using aluminium wire when MIG welding and
adjusting the amperage accordingly. Clean the panel
immediately before welding with a stainless steel
398 Repair of Vehicle Bodies
wire brush. If possible pre-heat the panel before
welding to give better weld quality and reduce
the risk of distortion. Control boxes are available
to convert conventional MIG welders to weld
aluminium (Figure 13.75).
13.18 Body electrical and
electronic systems
There are very few body panels on current vehicles
which do not have some form of electrical or electronic
device attached or nearby. This means that
the repair of any of the panels will probably require
contact with an electrical component or the power
supply to a nearby component. This section aims
to look at the basics of body electrics as may be
tackled by the personnel in a body repair shop. For
more complex systems and system fault diagnosis
the services of a vehicle electrical/electronics
specialist should be sought.
Electrical terms
Amp
The unit of current is the amp and is the quantity
of electricity which flows in a circuit. If it were
water you would refer to it in gallons or litres.
To measure current flow the ammeter must be connected
in series with the circuit, the ammeter must
be able to handle the expected current or it will be
burnt out. To measure large current flow, such as in
a starter circuit where the motor may be drawing
200 A, you will need an induction ammeter which
clamps over the starter cable without making electrical
contact. The most common use of an ammeter
is to check the charging rate of a vehicles
alternator; youll need a meter which goes up to 60
A for this job. A centre zero scale is useful for
measuring the current flow when working on vehicles,
as it can show the direction of the flow and
you do not need to change the connection of the
leads. Some ammeters which do not have a centre
zero have a button to change the polarity to show
charge or discharge.
Volt
This is the pressure of the electricity. The water pressure
from a fire hose can knock you over; the electrical
pressure from a mains socket can do the same.
Any voltage over 50 V is potentially lethal. Vehicle
electrical circuits operate at a safe 12 V or 24 V on
HGV/PSV applications. The reason for the higher
voltage on the large diesel vehicles is to reduce the
amperage needed by the starter motor, it also gives
better interior lighting in buses. The voltage in a
circuit is measured by connecting the voltmeter red
to positive and black to negative each side of a
component, that is, in parallel with the component.
Watt
This is the unit of electrical power.
746 W equals 1 HP.
Bulbs are usually identified by their wattage,
headlamps are typically 60 W.
Resistance
This is measured in ohms. If you have a narrow
hosepipe it will restrict the flow of water, in the
same way the diameter of the electrical wire will
affect the flow of the electric current. As a long
hosepipe will reduce the flow of water, the length
of the wire will increase the electrical resistance.
Resistance is measured with an ohmmeter. If there is
no resistance the meter needle will move across the
scale and read zero. Electrical cables and earth connections
should show zero or very small amounts of
resistance. An exception is plug leads which have an
inbuilt resistance for radio suppression purposes,
typically 30 000 ohms per meter of length.
Analogue and digital meters
Analogue meters are ones which have a needle
which moves across a scale; digital ones show
numbers on an LCD (liquid crystal display) or
illuminated display.
Resistor
A resistor is used to control the flow of electricity, it
allows electricity to flow, but the flow is at a set rate.
Capacitor
A capacitor (also called a condenser) stores electricity,
or absorbs current surges, for a limited period
of time. The capacitor in a distributor absorbs the
flow of electricity in the LT circuit when the CB
points open.
Resistance (ohms) _
Volts
Amps
Watts (W) _ Volts (V) _ Amps (A)
Craft techniques and minor accident damage 399
Diode
This is a one-way valve for the flow of electrical
current; zener diodes only allow electricity to flow
when the voltage exceeds a set figure.
Transistor
This term covers a number of different solid state
devices, including diodes. The most common transistor
has three connections, base, collector and emitter.
By applying a small current to one terminal a larger
current can be switched between the other two,
remove the small current and the larger current is
stopped. A thyristor is such that a small current starts
the flow which remains after the small current is
stopped. A thermistor is temperature operated, its
resistance may increase with temperature or it may
be of the negative temperature coefficient (NTC)
type where its resistance decreases as it gets warmer.
Series
This refers to a circuit where components are
connected in line with each other, that is, positive
to negative. As the number of items in the circuit
are increased the resistance will increase, and the
voltage across each component will decrease.
Parallel
A parallel circuit is one where items are connected
electrically alongside each other. The resistance
decreases and the voltage remains constant. Vehicle
lighting is connected in parallel.
Earth return
This is the name used to describe the use of the
vehicle body/chassis as a carrier of electricity. This
system is used on most cars and light vans, all
the circuits returning to the battery negative via the
body/chassis. The battery must have a good earth
connection. Tankers and buses use a two-wire system
where each component has a feed wire and a
return wire to the battery negative.
Short circuit
When a live bare wire or terminal touches the
chassis earth or another earth point it produces a
short circuit. This may lead to the wire becoming
hot and burning, even causing damage to the car.
Open circuit
When a wire breaks or becomes disconnected and
the circuit is no longer complete an open circuit is
produced. In this case the component involved will
not operate.
Fuse
A fuse is a breakable link in a circuit. The fuse will
blow instead of starting a fire in the case of a short
circuit.
SAE J1930
The Society of Automotive Engineers SAE
International have a task force to produce a list of
standardised terms and acronyms for automobile
electrical and electronic systems. The table below
lists some of the common terms.
Standardised term Standardised acronym
Accelerator pedal AP
Air cleaner ACL
Air conditioning A/C
Charge air cleaner CAC
(intercooler)
Data link connector DLC
Diagnostic test module DTM
Diagnostic trouble code DTC
Distributor ignition system DI
Electronic ignition EI
Engine control module ECM (Engine ECU)
Engine coolant temperature ECT Sensor
sensor
Engine speed sensor RPM Sensor
Exhaust gas recirculation EGR
Fan control FC
Generator (alternator) GEN
Ignition control module ICM (Ignition ECU)
Intake air temperature sensor IAT Sensor
Knock sensor KS
Malfunction indicator lamp MIL
Manifold absolute pressure MAP Sensor
sensor
Mass air flow sensor MAF Sensor
On-board diagnostic system OBD System
Open loop OL
Park/neutral position PNP Switch/Sensor
switch/sensor
Scan tool ST
Service reminder indicator SRI
Throttle body TB
Transmission control module TCM
(Transmission ECU)
Turbocharger TC
Vehicle speed sensor VSS
400 Repair of Vehicle Bodies
Battery
The battery is the source of power for starting
the vehicle. Most vehicle batteries are 12 volts.
Before carrying out any dismantling which entails
disconnecting any electrical or electronic components
or connections it is good practice to disconnect
the battery. Always disconnect the chassis
earth lead first and re-connect the same lead last. It
is good practice to remove the battery completely
from the vehicle and put it on charge to ensure that
it will re-start the vehicle when the repair is completed.
The battery must always be disconnected
before any arc/MIG/TIG welding is carried out to
prevent damage to the electrical system by the high
voltage of the welding apparatus.
Before disconnecting the battery you should ensure
that the security codes are available for the radio/cassette/
CD player. Also, if appropriate, any other security
item codes or personal setting are stored.
Some special vehicles have two batteries. One
battery for starting the engine, and one battery for
maintaining the supply to the electronic components
that operates when the vehicle is not running. The
second battery is usually a gel-battery. This is used
to maintain a power supply to the clock and the
security system, when the vehicle is parked. In this
case, both batteries will need to be disconnected.
Alternator
The alternator generates the electrical power to
charge the battery when the engine is running. The
rectifier inside or, in some cases, near to the alternator
contains a number of diodes. These diodes will
be damaged if the alternator is not disconnected
before carrying out any form of electrical resistance
welding. Disconnecting the battery will usually also
disconnect the alternator.
Electronic control unit (ECU)
Vehicles are fitted with at least one ECU. The ECU
may also be called by other names including ECM
or brain. Typically ECUs are used for the engine
management system, the ABS, the security system
and electronically controlled transmission systems.
ECUs are usually attached to the panel with two
screws. They are connected to the wiring loom with
a 32-pin plug. Pull back the spring clip holding the
connector plug into the ECU then pull the 32-pin
plug out gently without pulling on any of the wires
as this may pull the wired out of the connector.
Before replacing the plug ensure that the plug and
ECU are both clean and that each of the 30 pins are
aligned before pushing them into the ECU.
Central locking
Central locking may be operated with or without a
key. The keyless type uses either an infrared or a
wireless signal to a sensor on the vehicle from the
key-fob control, or zapper. The small mercury
battery in the key-fob control should be replaced
every two years. The central locking mechanism
may be operated by either a centrally pumped
pneumatic system or individual solenoids. Look out
for the locking mechanism when working on vehicle
doors. Always ensure that the connections are in
place before re-fitting the door trim. It is good practice
to ensure that the windows are wound down
before testing the central locking mechanism.
Electric windows
Most electric windows are operated by a small
electric motor and a continuous cable system. The
cable is only about 3 mm in diameter and will
break if subjected to normal rusting. The cable
goes stiff and brittle when rusty. The windows may
be operated by switches on either the centre consul
or the inside door trim. Some have two switches
for each window arranged to work in parallel. You
will need to disconnect the electric window power
supply leads and the central locking wires from
inside the door, after removing the door trim,
before attempting to remove the door or repair the
door skin panel. Figures 13.76 and 13.77 shows
some of the electrical components inside the door
of a Mercedes McLaren SLR.
Electric sunroof
Electric sunroofs operate in a similar way to electric
windows. The control for these is usually a switch
mounted just in front of the interior rear view mirror.
Access to the sunroof usually entails removal of
the interior head lining (also called roof lining).
Electric seat
Electric seat controls are usually available for
height, backwards and forwards position, rake and
tilt. Some seats have memory settings available for
different drivers, referred to as setting 1, 2 and 3
and so on. The connectors for these are usually
underneath the seat cushion. Be careful when
Craft techniques and minor accident damage 401
disconnecting and re-connecting the seat wiring
because seats also may incorporate an electrical
earth cable to reduce the risk of travel sickness and
connections for the pyrotechnic anti-submarine
seatbelt pre-tensioner.
Lights
Most light fittings are screwed to the front panel or
wing. Removal is usually simply unscrewing and
unplugging the cable socket. Re-fitting is the reverse
procedure. However, the head lamp beams will need
adjusting using a beam setter to ensure that they do
not dazzle on-coming traffic and comply with the
VOSA regulations.
Supplementary restraint system (SRS)
Restraint systems to protect the driver and passengers
in the event of an accident are designed to work
in conjunction with the vehicle body crumple zones,
the idea being to slow down the vehicle occupants in
a controlled manner. That is, if the vehicle hits a
wall, then the occupants will decelerate at a gentle
rate as possible in the time available. Typically, the
amount of time is 120 ms (0.120 sec) the time it
takes to blink. One of the major causes of death in
car accidents is damage to the brain caused by
deceleration rates which are too high.
The standard three-point seatbelt is defined as
the primary restraint system. Other features, namely
seatbelt pre-tensioners and airbags, come within the
category of SRS.
Airbags
The air bag is designed to protect the occupants
head and upper torso not to take all the weight
of the body. It is inflated by gas generated by the
pyrotechnic device. The gas is usually nitrogen
which is inert and poses no after-effect problems.
The air bag module, comprising the airbag, airbag
cover, the pyrotechnic device and its fitting must
be treated with extreme care when working on the
SRS, or any other related system. For instance, if
you are replacing the indicator or ignition switch,
you will probably need to disturb the airbag
module. The pyrotechnic device is ignited by a low
voltage electrical current and small tablets fill the
airbag with nitrogen in about 30 ms (0.030 sec).
Always carry, or handle, an airbag module so
that it is kept in the upright position. If the module
were to accidentally go off, the bag would inflate
upwards and the heavy part of the module would
go down to the floor. Airbags can not be repaired,
and any tampering is probably on a par with taking
the pin out of a hand-grenade and hoping that the
handle will stay in place.
Control unit
The control unit, sometimes called the diagnostic
and control unit, is central to the operation of the
SRS and is a form of ECU. The unit has three jobs:
it monitors the system for faults, controls the operation
of the airbag and seatbelt pre-tensioners, and
stores electrical charge for emergency use. The
electrical charge is stored in capacitors within
the control unit, so if the main vehicle battery is
Figure 13.76 Mercedes McLaren SLR tyre pressure
sensor
Figure 13.77 Mercedes McLaren SLR door
402 Repair of Vehicle Bodies
damaged or disconnected before or during impact,
the capacitors can supply an electrical charge to
ignite the pyrotechnic materials in the airbag and
seatbelt pre-tensioner. As the electrical current
from the control unit can operate the SRS independently
of the battery, obviously precautions
must be taken to avoid accidental operation before
working on the SRS. Typically the procedure is to
switch off the ignition and completely remove the
key, then disconnect the battery remember
always to remove the earth lead first and then
wait about 10 minutes for the capacitors in the control
unit to discharge themselves. The capacitors
will re-charge when the battery is reconnected,
before the ignition is switched on, so it is prudent
to ensure that nobody is in the vehicle in case there
is a fault which might accidentally operate the SRS
when you are first re-fitting the battery terminals.
Release sensors
Most vehicles are fitted with two negative acceleration
(deceleration) sensors wired in series. This is
a form of logic gate so that the airbag and seatbelt
pre-tensioners can be activated only if both sensors
agree. The sensors may be fitted in a number
of different places. Generally the main crash sensor
is located close to, or in front of the vehicle
centre of gravity, and is usually bolted to a longitudinal
structural member of the body/chassis.
The crash sensor operates the SRS at a deceleration
of about 15 g, that is like hitting a wall at
20 mph. The second sensor, called the safing sensor,
will trigger at about a tenth of the crash sensors
deceleration, that is at about 1.5 g. If a sensor is
faulty, the control unit should find it and illuminate
the warning light.
Rotary coupling
The SRS rotary coupling, between the steering
wheel and the outside of the steering column,
is unlike any other electrical coupling. It is not
a friction terminal. The SRS rotary coupling
consists of a length of wound wire ribbon which is
permanently connected at both ends so that there is
no risk of a bad connection. The ribbon coils and
uncoils inside the coupling housing as the steering
wheel is turned. Before removing the coupling, the
steering wheel must be centralised and the road
wheels set to the straight ahead position.
Wiring harness
The SRS wiring harness is a special construction;
do not attempt to replace any damaged wires or
change the plug terminals. The wiring harness
can be damaged by heat, so if an airbag or seatbelt
pre-tensioner is fired the SRS wiring harness
must be replaced too. Similarly, if the vehicle
suffers from any fire damage, the SRS wiring
harness must be replaced. The damage caused
by heat can not always be seen from a visual
inspection.
Warning light
The warning light is usually located on the dashboard;
but sometimes can be found on the airbag
casing in the steering wheel. When the ignition is
first switched on, the warning light will illuminate
for between three and five seconds to indicate that
the system is functional and that the control unit is
carrying out a self test of the system.
The amount of time that the lamp is lit indicates
the length of the system check. If the system is
correct the light will go out. If the light stays on
then the system has a fault. On some vehicles the
warning lamp will flash to indicate a fault code
this may need to be triggered by a diagnostic tool.
Some vehicles have an SRS OFF switch. This is
useful when carrying babies or small children in
seats which are protected by airbags, or the seatbelts
are used as part of a child restraint system.
Usually, a small white lamp adjacent to the switch
is illuminated when the SRS is in the switched off
mode.
Safety check
Do
Check all procedures in the workshop manual
before working on the SRS.
Ensure that all replacement parts are of the correct
type and in good condition.
Carry out any diagnostic procedures using the
correct equipment.
Carry and store the airbag with the cover facing
upwards.
Keep all SRS components dry.
Store all SRS components in a locked safety
approved area.
Ensure that nobody is in the vehicle when
re-connecting the battery.
Craft techniques and minor accident damage 403
Do not
Drop any SRS components.
Ever rest anything on an SRS component.
Place an SRS component near electrical equipment,
any source of heat or flames, or anything
which gives off electromagnetic radiation.
Carry SRS components inside the passenger
compartment of a vehicle.
Attach anything to, or otherwise mark components.
Attempt to tamper, dismantle or repair any
components.
Attach any other wires to the SRS circuit.
Crash sensors
As well as the release sensors for the SRS, many
vehicles are fitted with a crash sensor which cuts
off the fuel pump in the event of a serious impact.
This can usually be reset by pressing a button on
the actual sensor. The sensor is usually positioned
behind the glove box.
Security and alarm systems
On most vehicles there are three different systems
in operation:
Immobilisation An electronic system, usually
in conjunction with a key, or a key pad, that
immobilises the engine unless the correct key is
inserted or the correct numbers are entered in
the key pad.
Perimetric A series of micro-switches on
the doors, bonnet and boot which set off the
alarm if they are opened when the system is
alarmed.
Volumetric A sensor inside the car which
senses movement or changes in pressure if something
moves inside the car or a door is opened.
Air conditioning
Air conditioning heat exchangers (or radiators)
are often incorporated in, or mounted adjacent to,
the cooling system radiator. Be very careful
when dealing with air conditioning radiators
and other parts. The fluid in the system is under
pressure and should be safely removed before
disconnecting any parts. After changing parts
the system will need re-charging and re-setting
this requires special equipment. On older cars the
air conditioning fluid was R12 this contains
CFCs and must not be allowed to escape as it
causes damage to the ozone layer and can poison
the operator. An expensive evacuator and re-filler
is needed to re-charge the air conditioning
system.
Fuses
You will find up to 20 or more individual fuses on
vehicles. Do not replace a blown fuse unless you
are sure that the circuit fault which caused the fuse
to blow as been repaired.
Sensors
When carrying out body repair look out for
sensors. Sensors for a wide range of uses are
fitted, including outside temperature sensors, rain
sensors and on the Mercedes McLaren SLR
(Figure 13.76) tyre pressure sensors on the wheel
inner arches.
Checklist
After completing any repair it is a good idea to
check all the electrical/electronic components. A
PDI checklist for the particular vehicle is useful
to do this job.
Suggested further reading
Tom Denton, Automobile Electrical and Electronic
Systems, Elsevier, ISBN 0 7506 6219 0.
Allan Bonnick, Automotive Computer Controlled
Systems, Elsevier, ISBN 0 7506 5089 3.
Questions
1 Describe, with the aid of sketches, the processes
of hollowing and raising. List the necessary tools
for these processes.
2 Describe the process of planishing.
3 Compare the differences between planishing
and wheeling a panel to produce a smooth
surface.
4 Explain the method and name the tools used in
fabricating by hand an aluminium component with
a high-crowned surface.
5 State two important conditions to be observed
when using a wheeling machine.
6 After extensive wheeling on an aluminium body
panel, the metal becomes work hardened.
Describe a method used to anneal the panel, and
404 Repair of Vehicle Bodies
a workshop test which will indicate when the
correct temperature is reached.
7 Describe, with the aid of sketches, the technique
of split and weld for producing a hand-made
panel.
8 What are the purposes of forming angles and
flanges along the edges of sheet metal panels?
9 With the aid of sketches, describe three methods
of edge stiffening a sheet metal body panel.
10 Explain the terms direct hammering, indirect
hammering and pick hammering, as applied to
body repair techniques.
11 Describe the technique of cross filing.
12 Describe, with the aid of sketches, three different
methods of using a portable hydraulic body jack
in the realigning and straightening of vehicle body
damage.
13 Explain each of the following stages of repairing
a front wing which has received minor damage:
(a) the analysis and assessment of the extent of
the damage (b) selection of the appropriate tools
needed to carry out the repair (c) the repair
techniques required (d) the alignment and final
check.
14 Explain the process of body soldering when used
in the repair of a damaged body panel, and list
the necessary equipment.
15 Describe, with the aid of sketches, the technique
of hot shrinking to restore a panel to its original
contour.
16 Explain the difference between the hot shrinking
and cold shrinking techniques.
17 When is it considered necessary to fill with body
solder, in preference to any other method of repair?
18 Describe a method of repairing a sill panel which
is showing signs of corrosion.
19 What precautions must be taken, after body
soldering a repair, to prevent subsequent paint
defects?
20 Explain the importance of tinning a panel before
commencing body soldering.
21 State the disadvantages associated with the use
of hydraulic push rams when used on the inside
of a vehicle.
22 Give one practical application of the body jack
when being used for each of the following
operations: pushing, pulling and spreading.
23 Describe a suitable method of removing the
damaged skin during the repair process of
reskinning a door panel.
24 Explain how a new door skin is secured to the
door frame, and list the tools required.
25 Indicate the type of welding necessary when
securing a new door skin to the door frame.
26 Why is it important to clean the underside of a
damaged panel before commencing repairs?
27 Illustrate a tool which could be used in the
removal of damage from a double-skinned
section.
28 When, and how, would a pin welding gun be used
in repair work?
29 What type of attachment would be used on the
end of a body jack to spread the force of the
load during a repair?
30 Explain the differences between a hydraulic push
ram and a hydraulic pull ram.
31 The lower section of an A-post has suffered
corrosion damage. Explain a suitable method
of repair.
32 Describe a suitable process for the removal of
spot welds from a body panel without distorting
the flanges.
33 Describe the sequence of repair (not
replacement) to a rear quarter panel which has
received minor accident damage.
34 With the aid of a sketch, show how a body jack
can put a door panel in tension.
35 A small corroded area of a wing needs a patch
repair. Explain how this process will be carried
out.
36 Describe, with the aid of sketches, how the
hydraulic system of a body jack works.
37 With the aid of a sketch, show the techniques
involved in the manufacture of a small doublecurvature
panel by hand.
38 Describe, with the aid of a sketch, a vector pull
for correcting vehicle body alignment.
39 Explain why careful study of the accident damage
is important before any stripping or repair work is
carried out.
40 Explain the importance of correct alignment when
fitting new body panels and state how this is
achieved.
Major accident
damage
14.1 Damage classification and
assessment
Damaged bodywork is corrected by first observing
the extent of the damage, then deciding how it was
caused and the sequence in which it occurred. The
resulting damage can be classified into two groups:
Direct or primary damage This results from the
impact on the area in actual contact with the object
causing the damage. This will result in the largest
area of visible damage and is the cause of all other
consequent damage. Primary damage is identified
by first determining the direction of the primary
impact. This knowledge will help in the search for
concealed damage.
Indirect or secondary damage This is usually
found in the area surrounding the direct damage
which causes it, although in certain cases it may be
some distance from the actual point of impact.
After the impact, internal damage is caused by the
forced movement of objects and passengers
towards the point of impact, and can be seen in
the form of damaged dash panels, broken seat
frames and twisted steering wheels.
These two groups can each be subdivided in two
further ways:
Visible damage This is damage that can be readily
seen in the area of actual contact, such as a vehicle
having suffered frontal impact causing damage
to the bumper, grille, bonnet and front wings.
A detailed examination may discover distortion of
the inner wing valances, which would indicate visible
indirect damage.
Concealed damage This is indirect damage, but is
not easily detected by visual examination unless the
vehicle has been partially dismantled to allow a
detailed inspection. In most situations measuring
equipment in the form of body jigs must be used
to detect concealed damage, because complicated
monoconstructed vehicles may hide further damage
such as misalignment, which could therefore affect
the steering and roadworthiness of the vehicle.
Direction of damage
Direction of damage, or line of impact, is particularly
important to the body repairer. It is used to
identify the sequence and direction in which the
damage occurred, and consequently the reverse
sequence to be followed for the repair. Direct damage
marks are usually scratch marks where the
paintwork has been damaged; they are an excellent
guide to what happened, and indicate the possible
location of any hidden damage.
By careful study of the damage sustained it should
be possible to ascertain the direction and strength of
the impact force, and this is always the preliminary
stage of a detailed assessment.
Methods of describing major damage
Parallel side damage is caused by the impact
object moving parallel to the vehicle and causing
substantial damage along the full length of the
side of the vehicle, e.g. wing, doors, rear quarter
panel.
Direct side damage is caused when the vehicle is
struck at an angle to its side, causing substantial
damage at the point of contact.
Front-end damage is the result of head-on collision,
collapsing panels from the bumper to the
front bulkhead.
Three-quarter frontal damage is the result of an
angled front end collision, sustaining damage to
one front wing, the grille and bonnet.
Rear-end damage is the result of an impact direct
or slightly angled, to the rear end of a vehicle and
406 Repair of Vehicle Bodies
causing substantial damage to bumper, rear panel,
boot lid, boot floor panel and quarter panels.
Roll-over damage is caused by the vehicle rolling
completely over and returning to its wheels. In some
cases this type of movement could cause damage to
almost every panel.
Total write-off is damage so extensive that the vehicle
is either unrepairable or the total cost of repair
would be greater than the value of the vehicle.
The proportions of damage sustained in different
directions is shown in Figure 14.1.
In order to deal with the major damage which
occurs to the mono constructed vehicle, specialist
equipment has been developed. The equipment
consists of frame and body straighteners to pull the
damaged body shell back into alignment. These are
used in conjunction with body repair, alignment and
measuring jigs and thus provide accurate location
points where exact positioning becomes critical,
especially when the panel assemblies carry major
mechanical components and suspension units.
The new generation of pulling and pushing equipment
began in the 1950s with the introduction of
Dozer equipment, which enabled the repairer to use
external hydraulic pulling to aid the repair. Then
came the idea of repairing a vehicle on an alignment
jig using attachable/detachable brackets, so that it
was unnecessary to check the repair after every pull.
Next came the universal measuring system or bracketless
jig, which involved a measuring bridge or in
some cases laser measurement. Multipulling repair
systems were introduced, which were either static or
mobile and which used the vector pulling principle.
Later came mobile jig benches and lift operated systems
with pulling attachments. Finally, dual repair
systems give the repairer the advantage of precision
measuring allied to the use of brackets.
The types of pulling, alignment and repair systems
described in this chapter include the following:
1 Portable pulling equipment (Dozer system)
2 Stationary pull-post systems (floor anchored)
3 Stationary floor mounted rack (Korek system)
4 Stationary floor mounted rails
5 Floor anchored or anchor pot pulling systems
(Mitek)
6 Stationary bench-type jig mounted pulling
systems (universal or brackets)
7 Mobile bench-type jig mounted pulling systems
(brackets, mechanical measuring, electronic
measuring, laser measuring)
8 Mobile bench-type jig mounted pulling system
using universal brackets
9 Centre-post hoist jig system with pulling
equipment (brackets/measuring)
10 Four-post hoist jig system (brackets/measuring)
11 Scissor-type hoist jig system with pulling equipment
(mechanical or electronic measuring)
12 Drive-on bench systems with tower ram pulling
(mechanical or laser measuring)
13 Multifunctional repair systems with pulling
and measurement systems.
Figure 14.1 Proportions of damage sustained in
different directions in UK accidents (Motor Insurance
Repair Research Centre)
14.2 Pulling, alignment and repair systems
used on major accident damage
Since the monocoque construction of car body-work
based on engineering principles took the place of
coach-built bodies mounted on a separate chassis,
the whole concept of repair work has undergone
radical changes in both methods and the equipment
employed. Repairs to damaged body shells mean a
great deal more than the beating out of a few dents,
or even the cutting away of a damaged portion and
welding in a new pressing.
The majority of motor cars on the road today are
of unit or mono construction. Instead of a body
built on to a chassis, the whole unit is constructed
round a fra
