Obessive Compulsive Disorders - 1. Suspension

It's been a while but the snow eventually melted, then I was ill for a couple of weeks - so now its time to get back into the garage to start on some of those winter jobs.

First on the list - suspension settings. After Andy test drove the car after the fitting of the anti-roll bar down at GD, he recommended that I tweak the camber settings a little. The first step is to establish the starting point?

Now Santa had very kindly brought me one of these:

Very handy - loads of features and accurate to 0.05 degrees (3 minutes). The next step was to cut to length a piece of steel angle (magnetic base on the level) to fit on the wheel rims: Note the electrical tape on the ends to avoid scratching the rims. It then becomes quite a simple task to measure wheel cambers (after removing the spinners) :Before actually measuring the wheel cambers I checked all the ride heights. The car had not been jacked up since it was last driven into the garage, but still I rolled and "bounced" it back and forth a couple of times to ensure the suspension was settled. I then check the ride heights side to side at the front and rear. These checked out to be only 1mm different at the front and 2mm different at the rear - good enough.

In reality you should carry out suspension angular measurements on a level surface - my garage floor isn't level - but is pretty smooth and flat as evidenced by the uniform ride heights. The alternative is to measure the angle of the floor and adjust the measure angles accordingly. I did this my measuring the angle of a couple of the horizontal chassis rails.

I found that the car sloped down to the offside by 0.25 degrees - probably good enough for the builder of my garage floor! After measuring the wheel cambers I subtracted the floor slope to get the following results:

Hmmm...... 2 Wheels camber the right way at least!.... one doesn't camber at all and the remaining one cambers the wrong way! To be honest these aren't massive deviations. For the Jag Chassis with 18" wheels GD recommend 0.5 degrees negative camber on the rears and 0.75 degrees negative camber on the fronts.

I've got a couple of print-outs from having the tracking adjusted on the four wheel laser aligner down my local tyre place - the problem was that I didn't know which was the last one as they had no dates on - with these measurements I now know which the latest one is as the measurements are pretty close - all within 0.2 of a degree.

Now a lot more thought has gone into the design of the Jaguar Suspension than you may think. A quick look in any XJ6 service manual will reveal the following:

One 20 thou rear camber shim adjusts the camber by 1/4 of a degree.

One 1/16" front camber shim adjusts the front camber by 1/4 of a degree.

Simples!

So this would indicate that I need to do the following:

Front near-side: Measured -0.8 deg, Target -0.75 deg: Leave as is.

Front off-side: Measured 0 deg, Target - 0.75deg: remove 3/16 of shim.

Rear near-side: Measured -0.1 deg, Target -0.5 deg: remove 2x20 thou' add 1x10 thou' shims.

Rear off-side: Measured +0.55 deg, Target -0.5 deg: remove 4 x 20 thou' shims.

Before embarking on this I'll just double check my measurements.

Obviously things have changed since the build?????

• Initially the cambers were set at an estimated ride height - the actual ride height has changed a few times since the car has been on the road and with the unequal length wishbones there will be a noticeable camber change with a change in ride height.
• The front suspension was set up before the engine and the chassis brace were fitted - I had to jack one engine mount up to get the chassis brace in - and this would have had an effect on the position of the top wishbone pivot.
• The original camber gauge I used was a graduated bubble affair - nowhere near as accurate as the one I have now.
• The front camber were a little uneven at build and as I only had 1/4" camber spaces I just fitted them and forgot to remember to check it later..... until now.
• There is a limit to the accuracy that can be obtained by "reading a bubble" so even when setting the chassis level with a conventional level errors may well have crept in.

So to some extent during the build you are guessing a bit. Only when you have your chosen wheels and tyres and settled on a ride height will you be able to set things exactly.

My only worry now is that in those locations where I need to remove shim I hope there is actually enough shim in there to remove!

Watch this space........

**** STOP PRESS ****

Handy things these blogs..... just looked back through the suspension build up sections - I used 1/4" camber spacers on the front - so the offside just need to be replace with a 1/16" shim (3/16" removed) - I also used 4 x 20 thou' camber shims on the rear so I can remove them all.