Hello All,
My 98 XK8 has been vibrating heavily at highway speeds after I started driving it this season. I brought it into the shop to have the tires rebalanced and for a wheel alignment, but it's having the same problem. It's most noticeable around 50MPH and over. Here are some fun facts:
-Shakes more when I take my foot off the gas, but not when applying brakes.
-After the balancing and aligning, I decided to check the tire pressures, and they were way off. One was in the high 40s, ranging down to high 20s. I adjusted down to 26 front and 28 rear and it vibrated more, I then readjusted to 32/34 and it's a bit better.
-Car is smooth at lower speeds, to the point where I almost get surprised when I get on the highway and the car starts shaking.

I'm going to go back and demand they rebalance and realign my car out of principal since they didn't check these before doing the procedures, but, I don't think this is the solution to my problem.

Thoughts?

 

Almost sounds like a u-joint/half-shaft problem if it changes with foot off the gas.


Dave

 

ExKay8, are you feeling it in the steering or just a all over thing. Dave may be right on the U joint or at least something in the drive train.


Wayne

 

I don't feel much of the shaking in the steering, mainly in the chassis

 

Do you know if the U joints in the axles have ever been greased. There are four joints that have fittings and it's been noted, even the dealerships didn't know they were there.


Wayne

 

I don't think that's ever been done

 

If you think that will help, I would appreciate an explanation of exactly where and what needs grease and I'll bring it to the mechanic

 

ExKey8, from the differential there are two axles that go out to the wheels. Each axle has a U-joint on the end of it with a standard grease fitting, if they have never been done you will need to check for play as greasing them may be to late and one side or both will need replacing. Never do only one end. Get you man to check for excess movement.


Wayne

 

I agree with Dave, have you tried bringing the speed up to around 70 to 80?

Does the vibration dissipate?

There is also a busing at the end of the transmission yoke the rubber could be failing.

Good luck!

 

Nope, TheVibration Does Not Dissipate At Higher speeds

 

My Mechanic Is Suggesting Inner Tie Rod Ends, HeSays ThereIs Excessive Play OnThe DriverSide tire

 

That you should be able to feel through the steering wheel...



Dave

 

If you let it sit throughout the winter, you could get flat spots on the tires. If all else fails, replace them. In addition to the u-joints mentioned above, a bad wheel bearing can cause a vibration also.

Brett

 

Hi ExKay, sometimes process of elimination. I agree, as a member mentioned, tires do get flat spots which will cause vibrations a balance job will not repair. Easy test you can do is to bring the tire pressure up to the max as stated on your tires. If you feel a change I would suspect the tires. My '99 XK8, and ' 72 Buick experience similar traits. I find with both cars changing the tire pressure will help get rid of the tire flat spots. Otherwise as noted stiff axle and or drive shaft joints would need a review.
Hope this helps, Rich

 

It might be worthwhile to find a shop or dealer with a vibration analyzer, like this.....

https://www.americastoolwarehouse.co...FdCCfgodZH8AcA

...... a pay them for an hour's labor or so to see what they come up with.


This sort of tool was mandatory for GM and Chrysler dealers. I strongly suspect Jag dealers have the same or similar. Very useful for narrowing down vibration problems....at least fairly severe ones. Minor vibrations....not so much, in my experience.

At minimum you can use it to determine if the vibration is wheel speed, engine speed, or driveshaft speed.

Cheers
DD

 

Right. And this requires removing (or at least disconnecting) the shafts to feel the motion/action of the u-joints.

Many will look at a u-joint and or give it a wiggle and, if no free play is felt, assume that it is in good condition. Nothing could be further from the truth. A stiff/binding/seizing u-joint might well show no external signs of a problem.....but can cause one heck of a vibration !

Cheers
DD

 

Come to think of it, I adjusted the tire pressures down to 26/28 and the vibration seemed worse. I then readjusted to 32/34. My tire's max PSI is 51, I was afraid to inflate it that high because I discovered some rubber cracking along the side wall, so I went to 45 and drove it, I couldn't tell a difference in the vibration between that and when it was at 32/34.

I'm thinking changing out the tires since it needs that anyway with the cracking, the date code on them says 2007, maybe it's time.

 

I would say, it is time. Regardless of tread depth, tires age. I would not drive on tires with cracked sidewalls.

And I would find another place for the tires if the first shop didn't call out the tire's condition as an issue.

Then see if you still have the vibration.

 

Considering the change from 26 to 32 pounds, I'd really suspect the tires. Belt run out. Changing the tire pressure will only show a change not a complete repair. Tire pressure change would not effect any one of the axle or drive shaft joints vibrations. I plan on checking my joints for lube as I was not aware the ability to lube them existed. I suggest you do so as well. And replace the tires. Rich

 

UPDATE: Problem solved !

I bought 4 new General G Max AS03's and the vibration went away. Thanks to everyone's help and suggestions. I paid $575 with tax so I think I got a good deal, plus a $70 mail in rebate.

Follow Up:
-The mechanic that said my tie rod was bad made a demonstration to prove that it needed to be replaced. While the car was up on the lift, he moved the tire side to side, and said it's normal to have a bit of give. Then he moved it top to bottom and said there should be no give and that's why I need the tie rod. There appeared to be more give top to bottom on the drivers side than the passenger side. Does this seem reasonable?