So last year when I replaced the front shocks, upper shock mount and upper control/wishbone bushings, I put the caster shims back the way there were from the factory.

However the caster settings are not "green" at the last several alignments done, and I want to correct this.

Caster numbers as of today (3/27) are:
Left Front: 5.7° Range: 5.9° 7.3° (Not to bad)
Right Front: 6.2° Range: 6.6° 8.0°

I need some guidance (no pun intended) as to adding/removing/shifting, etc shims to bring the Caster into "green."

I have found the following:
thick shim = 0.063" = 1.6mm; effects caster 0.04°
thin shim = 0.035" = 0.9mm; effects caster 0.2°

The above info seems backwards to me, I would think the thick shim would effect caster more than the thin shim; are these correct?

Thanks in advance

 

It is the location of the thick, thin shim that makes the difference, not the shim itself and a shim moving from front to back has double the effect.


That being said, I think that is suppose .4 and not .04 degrees for the thick shim.


For more caster, you want the upper ball joint to move back, so shim accordingly.


Leaving one thin in front and the rest in back should bring both sides into range. Use parallel strings to reset the toe and you should be good.

 

If the car is driving straight and feels ok, tyres wearing ok I'd leave it alone, altering caster can cause steering pulls.

 

Ungn: yeah that is what I thought as well...thick should be 0.4° not 0.04°...must be a typo on the page I pulled-up.
And yes need to add a bit more caster to both front wheels.
Currently have shims:
Left front: 2 thick, 1 thin Left rear: 1 thin
Right front: 2 thin Right rear: 2 thick, 1 thin

So yeah...leaving 1 thin in the front on both sides and the remaining in the rear would bring both front's into the "green." Would probably just take car in for another 4 wheel alignment so I can get the new caster numbers and get the toe-in correct. Besides, guy is a friend of mine, so I get a huge discount.


melhookv12: car is driving straight after the alignment was corrected after I corrected my error (refer to my "rear shocks changed" posting), but having no luck with tyre wear here lately as it seems the tyres find either a screw or nail in the sidewall, which has not been repairable, only replacement. Good thing for tyre hazard warranties!
Have "heard" your advice.

Just turned over 69000 miles, so not a high mileage XK8 by any means.

 

On the site somewhere is the Jaguar Repair Manual diagram showing the standard distribution of the shims. Search for it, then place the shims to give you maximum caster. It'll still be with specs because there simply isn't enough movement to exceed the spec. I know, I've done it.
With power steering, higher Caster angles within reason are not critical, too much may induce a shimmy but there isn't enough adjustment in the suspension to allow that.
With all the shims arranged to give maximum caster, your Jag will be very stable at speed, and drive like its on rails.
Regards,

 

Here you go;

 

WhiteBear: Yep, that is the diagram I used to put the shims back when I replaced the upper control arm bushings. This is also the diagram that has the incorrect info for the thick shim.

I think Ungn has the right idea to leave just one thin shim in front, although the right side is already that way so unsure of what I could do there.

 

I set my 98 XK8 and 05 XKR,
Left side, all shims at pack#1 position, no shims at pack #2 position.
Right side, no shims at pack#3 position, all shims at pack #4 position.
This will give maximum caster angle, and both sides were within specs.
Regards,

 

Yeah....that means I am only moving 1 thin shim from back to front on left side, and front to back on right side. Doing this should just bring-in the left side, but not the right.

I want to to the rear camber shims, remove the factory 4mm and put in 6.5mm ones.

More quality time with the XK8 ahead!

 

If your springs are old, they sag. Everyone knows that increases negative camber, but it also changes caster [and toe] angles. So the Lanny basically rebuilt his front end, spring donuts, bushes, etc., but the caster is still out of spec and my guess its due to camber b/c of worn springs.

There is another variable to further confuse the issue and that is caster differences for the crown of the road. Drive on the right side of the road, the crown is on the left and the car wants to 'go downhill' or pull the the right. Vice versa in the UK. And that is why Jag has different castor specs for US, UK and rest of the world (ROW).

I went through the same process as the OP of rebuilding the complete front suspension pieces including all rubber and even a new used aluminum front subframe to fix worn (oblong'ed) holes where the A-arm pivots pins, holding the shims, pass through. Trying to get everything back to new factory alignment specs with old springs proved impossible. MelhookV12 has the right idea. If tire wear, especially inside front is not an issue, then adjust camber to the steering wheel effort that provides a centered ride on nominally crowned roads... Not too heavy steering effort, and balance those two with the feel or weight of the steering wheel as it wants to return to straight ahead.

It is a hassle to change the shims, drive, come back, change shims, etc. However, when I did it this way, the car steered straight, the steering wheel returned to the straight ahead position without 'snapping back'. e.g., it tracked properly with a good road feel; and finally, the car did not veer left or right on most of the roads I usually traveled. After all this, I ended up getting an alignment at a qualified shop, and my castor was in the middle of US spec, the camber was slightly negative, toe was in the middle of range, and tire wear was even.

 

Completely agree that the springs have sagged as they are the OEM ones; replacing them would bring the camber/caster back into spec...will probably have to just do that and be done with it...was just wanting to avoid doing that for some reason...not sure why now...????

Going to be doing alot more traveling in the XK8 in the near future so it is going to be loaded down....new springs are needed...plain and simple fact/fix.

Thanks

 

Having a little extra negative caster is not all that bad. Most of the unnecessary tire wear is caused by tires scrubbing the pavement due to too much toe in or toe out. If you get your toe set correctly, I think you'll be fine running on old springs. I'm at 100K miles now, and everything BUT the springs has been replaced. I have little too much camber, but tire wear has been inconsequential due to that factor. Good luck.