RE: Wheel Shimmy Cured w/ Lower Ball Joints

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RE: Wheel Shimmy Cured w/ Lower Ball Joints - 4/12/2008 5:39:47 PM    FactoryJaguarTech Posts: 2972 Joined: 1/6/2008 Status: offline 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. _____________________________ If it ain't broke, don't fix it!!! (in reply to JagtechOhio) Post #: 21

RE: Wheel Shimmy Cured w/ Lower Ball Joints - 4/12/2008 5:46:42 PM    test point   Posts: 123 Joined: 3/23/2008 Status: online 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 let us know if yours really do fit and where you got them. (in reply to JagtechOhio) Post #: 22

RE: Wheel Shimmy Cured w/ Lower Ball Joints - 4/12/2008 7:08:03 PM    GordoCatCar Posts: 168 Joined: 12/7/2007 Status: offline 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 the body shake.    I can drive down the road with my right hand on the steering wheel and feel the wheel shake; while at the same time, I reach back with my left hand and put a couple of fingers across the gap 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 Hunter Roadforce. 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.  I always star pattern hand torque them to 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 using a Hunter Roadforce.  I want to ascertain that both the wheel and the tire sidewall stiffness characteritistics are not contributing to this vibration. (in reply to test point) Post #: 23

RE: Wheel Shimmy Cured w/ Lower Ball Joints - 4/12/2008 7:20:20 PM    GordoCatCar Posts: 168 Joined: 12/7/2007 Status: offline Regarding the rotor runout.  I retested because the first time I failed to snug the rotor down to the hub surface with a couple lug nuts.  This time runnout is .004 near the outer edge of the brake pad sweep.  One would think this is within acceptable range for this spec.  Tomorrow I will clean 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.   (in reply to GordoCatCar) Post #: 24

RE: Wheel Shimmy Cured w/ Lower Ball Joints - 4/12/2008 8:01:20 PM    JagtechOhio   Posts: 477 Joined: 3/12/2008 Status: offline 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. (in reply to GordoCatCar) Post #: 25

RE: Wheel Shimmy Cured w/ Lower Ball Joints - 4/13/2008 12:12:14 PM    GordoCatCar Posts: 168 Joined: 12/7/2007 Status: offline 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 qualified mechanic (SCCA pit crew and 15+ yrs exp. mechanic, etc.)  Naturally I eliminated wheels and tires as a contributing cause; and I 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 my QC program here. BTW I re-checked all hubs and rotors.  The hubs were .004 or less, the rotors were .006 (rear wheel) or less.   Gordo (in reply to JagtechOhio) Post #: 26

RE: Wheel Shimmy Cured w/ Lower Ball Joints - 4/13/2008 1:48:11 PM    JagtechOhio   Posts: 477 Joined: 3/12/2008 Status: offline 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 line on 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. (in reply to GordoCatCar) Post #: 27

RE: Wheel Shimmy Cured w/ Lower Ball Joints - 4/13/2008 5:32:29 PM    GordoCatCar Posts: 168 Joined: 12/7/2007 Status: offline I have the tubular cross brace under the engine bay.  I was one of the first subframe components I checked.  When Jag upgraded the early model chassis; what sort of enhancements were utilized?  Are there gussets or crossmembers that 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 bit tighter.  I want to lower it, but not unless I can stiffen it up first.  gordo (in reply to JagtechOhio) Post #: 28

RE: Wheel Shimmy Cured w/ Lower Ball Joints - 4/13/2008 7:05:07 PM    JagtechOhio   Posts: 477 Joined: 3/12/2008 Status: offline 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 suspension to 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-on pieces 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 to improve on the stock supports, if you have the hood 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. (in reply to GordoCatCar) Post #: 29

RE: Wheel Shimmy Cured w/ Lower Ball Joints - 4/13/2008 7:43:18 PM    GordoCatCar Posts: 168 Joined: 12/7/2007 Status: offline 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 is prohibitively flush against the bonnet insulation 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 tunnel backbone, 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. < Message edited by GordoCatCar -- 4/13/2008 7:45:29 PM > (in reply to JagtechOhio) Post #: 30

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