I've recently had the front and rear suspensions rebuilt in my XJS.
Front - new upper and lower bushings (OEM rubber), new ball joints (lemforder), new tie rod ends, GAZ shocks, new OEM springs to restore ride height, new subframe mounts
Rear - new fulcrum bearings, diff output shaft bearings, radius arm bushing (OEM rubber), Gaz shocks etc
The steering rack bushes were replaced around 12 months ago when the rack was rebuilt. They are poly.

Unfortunately the car doesn't drive as well as I'd hoped. Straight line stability could be better and the steering feels a bit vague/light at speed or under hard acceleration

The car runs 16 inch tyres from a later model XJS. 225/60 R16 rear and 225/55 R16 front.

Alignment is:
Front
Camber left and right is around -0.5deg
Caster is around 2.5deg left and right
Total Toe is +1.1mm

Rear
Camber, slightly negative but almost Nil
Total Toe +1.5mm

My first inclination is more caster is required and maybe some toe in rather than the current 1.1mm toe out. I've read comments where posters say to dial up the caster to the max spec. Can anyone advise how high this is? Any other suggestions? Thanks

 

Toe should be 0 to 1/2 a degree toe in (not sure what the + in "+1.1mm" means). Castor spec is 3.5 degrees positive + or - 0.25 of a degree, so you need about a degree more castor.
Also, some alignment places do not understand the correct procedure for toe in/out adjustment, which is:
Centre rack using the indentation
Adjust each side separately to the correct spec (I would suggest 1/2 a degree toe in).

Some places do all the adjustment on one side, whereupon the power steering is fighting the toe.

The rear toe (assuming + means toe in) is a bit more than spec which is parallel, but there is not much you can do about it, and it may go nearer to spec as the rubber beds in. However I would adjust the rear camber to 0.5 to 0.75 degrees negative, as this vastly improves the cornering grip and solid feel of the rear end. This is adjusted by removing shims from the drive shaft/brake disc/ differential flange join.

 

Toe out is your problem. Toe should be Zero or slight toe IN

 

Thanks for your responses. I had the toe back to front, I double checked and a positive toe reading is actually toe in, so I do have a small amount of toe-in front and rear. Converted to degrees for a 16inch wheel its about 0.17 deg toe-in on the front and 0.2 deg toe-in on the rear. Perhaps the front could do with a bit more.

I will also get more caster added

As for the rear camber, it's currently -0.18deg on the left and -0.37deg on the right. Your comments are noted Greg, although I might try and stick to the front adjustments (or should I say easier adjustments) first.

 

Also, it is worth checking the bearing play in the front wheels. I normally adjust the bearing nut to just, repeat just, zero play, absolutely not any tighter. If that is a bit too loose, you get more imprecise steering.

 

 

Did you put full weight on the car and settle the front suspension before you tightened the lower fulcrum shaft? Failure to do this will distort the lower wishbone bushes and will cause premature failure.

Yep the stub axle is very common, both mine were like that. I fixed this by machining spacers that fit between the inner and outer bearing to prevent them from spinning. They also set end float both sides, all I need to do is tighten the nut and install the castle cap and split pin

BTW Greg I had the whole thing apart recently to replace the front disks and the spacers I made between the front and rear bearings are still good.

 

That is good news; I reckon, as you said previously, they need to be made of hard steel, mine were normal mild steel. But now, as I have rebuilt the entire front end including a new subframe and all new parts, and as I eventually found the real trouble was the front six shots which I hardened up, and as it is absolutely perfect to drive, I shall not be doing any more to it!

 

The drag brace elestormatic puck on the forward drag braces are cracked
order new elestricmeric pucks press them in and no more drifting when you step on it.

Asumming you have checked the rear wheel and with the car jacked up grab the wheel try to move it in and out.
If it is realy bad you can do it with out jacking it up.

 

I believe you said you had to fill your six shots. Are there such things as six shots with solid rubber only(not poly).

 

Yes, Manners sell poly six shots with no holes and they are no dearer than the rubber ones with holes, I reckon they would be perfect. I would have bought some, but as my filled ones work fine I shall wait until they need replacing - if they ever do.
Greg

 

I have Poly in 6 shot and rack and they do sharpen up the steering a great deal.

 

But are there non -poly ones, basically just solid rubber ones.
And with poly six shots, do you have to fit the rear mounts with poly too? (For the front sub frame I mean)

 

Don't know if there are solid rubber.

My front subframe rear mounts are stock. The poly fronts reduce the sideways flex in the front subframe enough to prevent the shimmy that some report.

 

No solid ones, though I made mine solid by filling up the holes with gunk-stuff called Stixall.
Rear front subframe mounts are fine OEM, no poly ones as they are not needed.

 

Ok, gotcha...I guess no way to stop the side to side motion of the stock ones if that is the major issue with them? I'd be more than happy to install the poly ones but don't want to get that stiff ride that many complain about. Perhaps you'd only feel that kind of stiffness when applied to control arm bushings and that sort.

 

The six shot stiffening I did made no perceptable difference to the ride quality. What it did do was eliminate steering wheel oscillation at a certain speed. I think the latest batch of Metalastic bushes are not the same as the ones fitted 30 years ago, and on my car at least, they allowed too much movement (no idea if side to side or up and down), out of phase each side, of the front arms of the subframe. This unwanted subframe movement must have produced unwanted steering effects at the wheels and thus created shimmy in the steering wheel at 80 kph. I think you would be 100% OK with poly non-holed six shots, but if you found otherwise, or just in case, fill in the holes on your old rubber ones; but remember the gunk will take about a week in the boiler room to thoroughly dry.