Setting up the car for the road
From GTM Workshop
The front suspension of the GTM Libra utilises two unequal length wishbones on either side. These wishbones are attached to the monocoque through mounting brackets with shims. The camber angle of the front wheels can therefore be adjusted to the required angle. A small amount of castor angle adjustment is possible by fitting different size shims to the front or rear of any wishbones. The front upside down shock absorbers has adjustable spring seats for ride height and adjustable damping settings. Different spring rates can be obtained from the factory.
The rear suspension uses two trailing wishbones at either side. These wishbones have adjustable ends and therefore the camber angle can be adjusted. The coil over shock absorber unit has adjustable spring seat and adjustable damper settings. By carefully following the instructions below the amateur should be perfectly capable of setting the car to the standard setting advised by the factory.
Steps
The car suspension adjustment cannot be undertaken until the car is fully built and all the weight associ-ated with the build is on the suspension. The track on the front and the rear of the car is the same and therefore by using the front suspension as a guide and a suitable straight edge along the side of the car it is possible to set the suspension approxi-mately in the right position. At this stage set the rear camber angle at 0 degrees i.e. with the wheel vertical to the ground.
At this stage the sides of the sill can be used as a good guide as to the positions of the rear wheels side to side. Make yourself a ride height gauge by cutting a piece of wood or other suitable material to a size 5 inches in one direction and 5 1/2 inches in the other direction The 5 inches represents the ride height ender the front and rear parts of the sill when the car is fully loaded with passenger and driver and the 5 1/2 inches represents the height under the same position without the driver and passenger All settings can be made to the suspension geometry at the 5 1/2 inch ride height Adjust the adjustable shock absorbers to the minimum setting and adjust the adjustable spring height on the shock absorber to give you the 5 1/2 inches required the front and rear corners of either side sills The car should now be capable of being pushed around to enable you to find a suitable flat area on which to adjust the suspension more accurately. The area you choose must be as flat as you can possibly find.
With the car on the most level piece of ground you can find check the heights of the two front wheels relatively to each other with a spirit level and a straight bar placed on the ground between the two. It is possible to pack up one side of the car relative to the other using newspaper or magazines to get two wheels exactly level to each other. The same can be repeated at the back of the car to get the two rear wheels exactly level with each other. The relative positions of the back wheels relative to the front are not particularly important and therefore need not be adjusted. With the car all levelled in its final position recheck the ride heights to 5 1/2 inches taking into account any packing materials you may have used on the wheels.
Starting at the front of the car. Before any adjustment can be made to the toe-in at the front of the car it is necessary to determine the central position in the steering rack. Moving the steering wheel to one extreme measuring the amount of turn to the other extreme, halving the movement and determining the central position can do this. Once these central positions have been determined mark the top of the steering wheel with some masking tape and check that the movement left and right are the same. Once you're sure you have the central position it is a good idea to put the steering wheel itself with its spokes in the central position so that when you drive the car it can be clearly seen whether it is steering correctly.
Attain a straight bar that will run from the front of the front wheel to the back of the rear wheel. Holding the bar halfway up the wheels adjust the toe-in on the wheel to give approximately a toe-in on either side of 2 millimetres. On certain Metro steering racks you may find it necessary to remove a small proportion of the threaded end of the steering link to enable the correct adjustment to be obtained. This can be done using a suitable hacksaw and file, Repeat for the other side of the car. At this stage I have not covered the adjustment of the camber angles of the front wheels as in practice it had been found that this angle is pretty near correct straight out of the box.
The wheels at the front should be vertical and as long as your car does not deviate from this measurement unduly I would suggest that you leave it at present and tackle any changes at a later date. I have covered the methods of making adjustment to the camber angle at the front at the end of this write up, Moving to the back of the car the situation is more complex. Camber angle and toe-in are both adjustable as well as the track that the car runs at. The car runs with a rear camber angle of minus 1 1/2 - 2 degrees. This means that the top of the tyre leans in towards the car by 1 1/2 - 2 degrees. Set the camber angles to be around this figure by adjusting the top wishbone adjusting nuts on the outside face of the wishbone. Set the toe-in to be square with the front wheels i.e. neither toed in nor toed out.
Referring to the diagram and looking from the back of the car set the dimension five 550 millimetres on the driver’s side of the car from the face of the casting where the driver shaft protrudes to the centre nearest bolt on the bottom wishbone. To obtain this adjustment it is necessary to adjust only the bottom wishbone with the two locking nuts on the outside ball joint and then readjust the top wishbone to obtain the correct camber angle. Working similar on the passenger side adjust the distance from the face of the casting where the passenger side drive shaft protrudes to the centre of the first bolt on the bottom wishbone to 365 millimetres. Now readjust the top passenger side wishbone to obtain the correct camber angle. It is difficult to measure exactly these two dimensions but try to get them as close as you can. An accuracy of plus or minus 2 millimetres will be totally satisfactory.
A slight error in the track will not in any way adversely affect the handling of the car. Once you have set these bottom wishbones and locked up the lock nuts it should not be necessary to readjust them again.
Whilst the car is situated on a level ground it is advisable to repeat the hole of the setting up procedure again making sure that you are satisfied that everything is correct. Once satisfied that everything is correct adjust the rear toe -in to be between 3 and 4 millimetres at the wheel rim. This can be only be done by relating the back wheels to the front wheels as the wheels must be aligned to the car A convenient method is to place a straight edge along the wheels between the front and rear and then measure the distance.
The removal or addition of shims between the wishbone mounting brackets and the monocoque can obtain adjustment of the front camber angles. Always add the same amount of shims to the front and rear mounts of any one wishbone. Try to minimise the amount of changes you make by reducing the shims on the top wishbone and increas-ing the shims on the bottom wishbone for instance rather than just increasing the shims on the bottom wishbone. Any changes made here of course will necessitate the rear adjustment of the toe-in of the front wheels.
Your car is now ready to be driven but before doing so please recheck all the safety items i.e. brakes, steering, suspension to make sure that you are absolutely sure everything is satisfactory. Drive the car a short distance carefully and return and recheck all safety items. Check that the water level has remained constant and that there are no leaks from any fluids Set the front and rear shock absorbers to 10 clicks away from the minimum setting as a start.
