I'm in the UK and I have 2002 XK8 which just went in for a wheel alignment and to adjust the caster to try and tackle a lack of steering wheel returnability and a tendency for the car to follow the camber of the road. Unfornately the adjustment did not yield the results we were looking for.

Before Adjustment Caster:

Left Front: 5.46
Right Front: 5.11

After Adjustment:

Left Front: 5.52
Right Front: 5.58

The left side of the car had only 2 shims and the right side had all 4. To start off with we put 2 Thick and 2 Thin together on either side in the same position - between the subframe and the wishbone bush towards the back of the vehicle - which as I understand it would pull the upper wishbone backwards and alter the angle for maxiumum positive caster. However, after fitting and measuring, the caster has barely changed, aside from both sides being almost the same. Neither myself nor the technician could understand why this would not result in more positive caster so I'm wondering if any of you have any ideas or have we done something wrong?

For info the car has had the entire suspension replaced (standard). All bushes, balljoints, shock mounts (poly), links, wheel hubs, everything. Aside from the column, everything else at the front involved in steering has been replaced.

 

It is normal behavior for these cars to follow road surface imperfections, it’s called tramlining.

Re: steering wheel returnability, it is odd that your steering wheel does not return to the center. There is a correct arrangement for the thick and thin shims, but it varies depending on your location, USA, England, ROW.

 

This is exactly why we were confused. Putting four shims at Packs/Position's 2 and 4 should have resulted in maximum positive caster and yet the result is not at all what we expected.

The steering wheel not centering is odd and exactly why caster needs an adjustment, it is almost solely responsible for the steering wheel returning to the center and giving that sense of stability, particularly at speed.

I have had difficulty considering what else could be cause for the lack of positive caster after adjustment since little else is adjustable, which is why I'm reaching out here in case we've either missing something or there are other variables even after everything being replaced.

 

l will just point out, there is a typo in the ROW pack 1 in the above chart. Must be a total of 2 x thick and 2 x thin per side of car.

 

There is a potentially very dumb reason why this happened. Did they rotate wheels as well? or otherwise remove them? When I got my car, it had the front wheels on the right and the back wheels on the left... cos they are staggered 18s of different width, the last person to rotate didn't realise. As a result it had been aligned with a wheel 1 inch wider on one side at the front and the results were very off as a result. One of the observed problems was more tramlining in one direction than the other, and the steering wheel being off-center. So for a quick (and zero cost) sanity check, pull the wheels and read the sizes on the back to make sure.

My car had identical tires on all 4 wheels even though they were different sizes, so just by glancing at the tire sizes you couldn't tell the wheels weren't all identical. Might just be the case for you too. I have encountered several xk8 owners with non-staggered tires on their staggered wheels, presumably a relic of cost-saving in the past.

 

No the wheels are all where they're supposed to be. I'm not entirely sure how swapping them would change the caster setting at the hub, it's measurement is not defined by the wheels but the the variance between the two balljoints. You move shims to push the upper balljoint backwards or forwards.

The only ideas I have for why it's not greater are things like:

1. The upper wishbone bushes are the wrong way round, one side is thinner than the other.
2. The lower control arms are in some way sitting slightly further back.
3. Variance in the A Frame's construction means that it will never go into alingment using stock bushes and shims. The car is unlikely to have ever been in spec.

I think the latter is the most likely but there are potentially ways to work around this.

 

The uppers should all be the same, the lowers however are different between front and back lower arm bushing.
l actually recall watching a YouTube video some time back and the author had his front and back in wrong place.
My pics are of my poly so can only be used as a guide but it is possible that your front lower and rear lower have been fitted in wrong positions and lower assembly is now moved back on car by about 4mm from where it should be.
Much more chance of incorrect bushing placement than crossmember causing your trouble.

These are the two lower stock bushes, they are not the same offset. Forward bush is on the right.

Front lower arm should be biased toward front. Rear face of lower arm to front face of crossmember mounting tab should be 15mm. If it is closer to 11mm the bushings have been switched.



Edit. Just to add re possible switched lower bush positions. This screenshot shows the sellers can't even get it right. The bush being sold here is a front bushing, the diagram has been butchered with lower arms 180 degrees to crossmember orientation giving a confused perspective.

 

This is exactly what I was thinking, that there might be something incorrect with the lower arms.

I'll need to take a look next year when I get a chance but I would hazard a guess that either the lateral arm or lower control that joins to it have the bushes mixed up or possibly the same bush all round. I purchased these arms as a complete refurb and had them swapped. I don't fully trust the seller to have bothered making sure the bushes are different and correct.

I've still got the old arms and I can clearly see the difference so I might try and refurb them and then reinstall.

 

If both bushes used are the same the lower arm assembly will not physically fit up to the crossmember. Only two ways it can fit to crossmember, correct bush placement or correct bushes but switched in positions.