Maximum rotor runout spec for Jags is .004"
If you are having .010 I would say you need to determine if that is from rotor or hub. .010 on an XK would definitly cause a shimmy in the steering wheel.

 

The lugnut setup is why I was never able to find any aftermarket nuts that would fit. As JTO says the they are not normal, at least from my experience. Please letus know if yours really do fit and where you got them.

 

I agree about going back to the basics first. That's why I want to first eliminate the wheel tire combination from the equation.

The wobble in the steering wheel. Very slight, but at a different frequency than thebody shake.

I can drive down the road with my righthand on the steering wheel and feelthe wheel shake; while at the same time, Ireach back with my left hand and put a couple of fingersacross thegap between the rear of the door and the unibody. These are two separate sources of shudder or shake.

Did you try rotating the tires fr to rr one at a time? No, I will. But first I am getting them all rebalanced on a HunterRoadforce.

The OZ forged steel wheels are hubcentric, and fit the hub snugly. We checked runout on them before balancing the wheel. I didn't see the numbers, but tire tech said they ran true.

The lugnuts are a 60'taper seat. Ialways star patternhand torque themto 75ftlbs.

You have measured little radial runout, but if the wheel is not hubcentric you may have axial runout. That's why I want to get them rebalanced under load usinga Hunter Roadforce. I want to ascertain thatboth the wheel and the tire sidewall stiffness characteritistics are not contributing to this vibration.

 

Regarding the rotor runout. I retestedbecause the firsttime I failed to snug the rotor down to the hub surface with a couple lug nuts. This time runnout is .004 nearthe outer edge of the brake pad sweep.One would think thisis withinacceptable rangefor this spec. Tomorrow I willclean up the hub face and rotor surfaces with a machinist file to be sure the surfaces are flat and smooth;and then check runout again.

 

Gordo,

I had guessed that when I saw your .010, nobody ever snugs the rotor and you would have more significant symptoms. I don't think that's your problem.

I was going to suggest playing swap with your spare, most of the time they are a nice full size and brand new Pirelli. Then it dawned on me, you might not have a set of lugnuts to mount it with. It was a mistake people made all the time with Dayton wire wheels on XJ6/ XJS, they realized it the first time they had a flat. Better make sure you have a set.

 

Swap front to rears, on the drivers side eliminated about half the shake. I am definitely going in tomorrow for a roadforce balance. The car is not entirely smooth; however that one wheel/tire swap made a pretty big difference. I want to get the tire combo fully vibration free, then we'll go from there. I am hoping, after all the other work, wheels and tires will be the cure.

Good call Andrew on back to basics. I have new tires, and they were balanced by someone who I would consider a qualifiedmechanic (SCCA pit crew and 15+ yrs exp. mechanic, etc.) Naturally I eliminated wheels and tires as a contributing cause; andI was was off to blame more suspension parts as faulty even though I knew they had been checked pretty thoroughly. I gotta take another look at myQC program here.

BTW I re-checked all hubs and rotors. Thehubs were .004 or less, the rotors were .006 (rear wheel) or less. Gordo

 

Good news!

The thing to keep in mind, no matter how slopped out the front suspension is, it will not cause vibation unless lateral or braking loads are induced. Everything sits right where it is when you're driving in a straight lineon a smooth road. You'd have found significant play in the ball joints or leading lower wishbone bush if it was there, but they would not cause apparent symptoms unless you were traversing bumps, cornering the car, or using the brakes.

My guess is you have already fixed the problems that ate the old set of tires, and you will be fine once the new set is as good as it should be. Make sure you have a set of lugnuts for your spare, and happy motoring.

There is a cruciform beneath the engine to increase torsional rigidity, do you have the big "X" under your front end?That's part of the FJT cowl shake discussion, just a thought in case somebody pulled it and you didn't know it wasn't there.

 

I have the tubular cross brace under the engine bay. I was one of thefirstsubframe componentsI checked.

When Jag upgraded the early model chassis; what sort of enhancements were utilized? Are theregussets orcrossmembersthat can be retrofitted as bolt-ons, or welded?Is there anything in the aftermarket, or homegrown, like subframe connectors that might be used?

I'd like to get this chassis a bittighter. I want to lower it, but not unless I can stiffen it up first. gordo

 

I'm pretty much a bone-stock kind of guy, and here's another reason why...

If you lower the car, you're increasing the spring rate or the car will bottom all the time, right? Add some stiffer shocks to the equation, and you've lowered the roll center and stiffened the suspensionto decrease weight transfer,but you are now imparting increased load into a somewhat flexible monocoque. Holy cowl shake, Commisioner Gordo!

I do not know what improvements were made, sounds like FJT is our man on that subject. I doubt there are any other bolt-onpieces available, I just wanted to make sure you had the one that was already intended. You could probably fab some reinforcements between the two shock towers and tie it in to the cowl toimprove on the stock supports, if you have thehood clearance.

The XJS went through a series of improvements once they cut the roof off, the most significant of which was some honkin' big tubes in the rocker panels. Even so, some of the later cars exhibit much more cowl shake and rattled manners than others. I vote for a full roll cage.

 

Agreed. I certainly don't want a higher working spring rate if the chassis flex is going to be increased because of that.

I just looked at the possibility of a fabbing a strut [spring]tower brace. The top of the intake tubes isprohibitively flushagainst the bonnetinsulation padding. One might triangulate to the upper body crossmember which supports the radiator and electric fan shroud. I believe, however; body flex is more longitudinal and that strengthening the platform with a transmission tunnelbackbone, or as you noted, rocker panel stiffeners would be a more effective measure.
Needless to say, I do not see a six point in my vert's future.

 

One more footnote on this subject, before I close my ramble-hole.

I don't think these monocoques are very strong at all. I have seen a number of XK8's hit in a rear corner, sometimes not very hard, and it tweaks the tub enough to crease the opposite side quarter at the base of the rear screen. I think the cage would need alot more than six points.

 

GReat info... I wish you had some pix of the job

 

Follow up on getting rid of the shakes. (Sounds like an alcoholic subtitle)

The new Michelin Pilot Sport A/S'swere "rebalanced" using a Hunter GSP9700 RoadForce balancer. This machine balances while the tire is forced against a rotating drum w/ 1500lbs of pressure, duplicating real world conditions. Sophisticated technology checks for both wheel and tire runout, and other vibration inducing factors.

All of the four (4) tires wereout of balance. Two were so far off that the tire/wheel combinations were unmounted and clocked to more evenlymatch individual tire and wheel discrepencies. One tire was out-of-round beyond spec and will be exchanged by TireRack.

I will never again use anybalancing method except this type of RoadForce weighted procedure. Even with the out-of-round tire still on the rear, the car is 100% smoother at the steering wheel. As I have seen on other posts, these cars are super sensitive to the slightest of wheel imbalances.

With the front wheel shimmy fixed, it is now ever more apparent thata good deal ofchassis shake isgoing to be ever present. I am not used to driving cars with so much body flex in the platforms.I wouldlike to see what kind of fix can be done to strengthen the bodies on these verts. I have an idea that the door latch could be improved upon. I can were amore solid fit between the door and unibody couldtighten up the center structure of the car. Anyone heard of this idea before? gordo

 

Bo and Luke solved this vexing problem, although I think Cooder may have secretly had a hand in it.

 

1. Weld shut the doors.
2. Paint it Orange
3. Union Jack on the roof (Instead of Stars and Bars)
4. Short shorts and crop top for the GF

OK. I got my To Dolist. I'll see youguys in a couple of days w/ a followup report. Gordo

 

I got two more words on that subject...

Boogidee

Boogidee

 

Does anybody know of a shop in central CT that can reliably press new ball joints into the control arms of 99 xk8? I replaced the left lower rear control arm with ball joint, (PITA, But worthwhile). Removed 90% of all shake... But it came back!... Inspected yet again with a 6 foot bar on unloaded front end and the previously good right ball joint showing about an 1/8 in play. I want to get http://www.britishparts.co.uk/.sc/ms...%20JOINT%20KIT
but I don't have a press, and my prior reading indicates I should get a recommendation on a shop to use before I launch on this effort.
Thanks to all
Ghanks
"If you're not part of the solution you're part of the precipitate.."

 

I understand that the new ones have the ball joint installed. I was told that improper pressing could cause problems with the joint and this happens far too often.

 

The cost of the suspension kit which contains all 4 ball joints, all bushings, roll bar links and is ~$260 while the aftermarket control arms are $138 ea. (Local US price $270!)
The control arm is easier, but since I am going to strip it down all the way to replace the bushings and upper ball joints, it seemed to me that finding a compentent shop to handle the pressing would be the way to go. I have asked a local restorer but have not heard back yet.
Thanks

 

I'd try a post also in the regional section of the forum ghanks. I think you'll have better luck getting a response to finding a good mechanic. Good luck in your hunt.

OT, In hindsight on my project, I replaced all of my upper and lower control arm bushings in the front suspension. I wish now I would have just purchased and installed that ball joint kit where applicable.

And by the way Gordo, I've got a wheel shimmy (at 60mph however) that is now bothering me. Next weekend, road force balancing them and asking them to let me watch.