My X only has 21,000 miles on it, 6000 of which I've put on it in the last 6 months. I've had a very persistent problem that I can't seem to solve with simple measures. When I got the car it had a vibration at 32-35ish mph then steering vibration at 65-70 then it would morph to a high frequency thudding at 70+

I replaced the tires immediately as they were the originals, no change

I replaced the brake pads an rotors all the way around, no change

Greased my propshaft carrier bearing at least 3 times, no change

I replaced the oil, transmission fluid, TC fluid, and still no change

Now, after 6000 miles... the issue has changed a little... I get a very noticeable high frequency thudding from 32-35mph that abruptly stops after 35mph. It feels as if it's coming from the rear. At 65ish I have steering wheel vibration that morphs to the thudding still at 70 but past 80mph it smooths out nicely. The thudding seems to be worse when the car has warmed up a bit, however no change from warm to cold weather. It also only happens under load, if I let off the accelerator it does not happen.

If anybody knows definitively what this may be I would be incredibly greatful, I don't want to waste money chasing a phantom and replace all the moving parts. I'm thinking maybe its the propshaft but don't want to spend the money unless it is for sure. I'm also wondering if its bad CV joints all the way around??

Any insight is greatly appreciated!!!

 

check and or replace your engine mount

 

how would one know if the engine mount was bad just by looking?

 

Millertic, try rotating the tires front to rear and rear to front to see if the wobbling in the steering wheel changes. We have found that the rims on the car bend rather easily and that will cause a wobble in the steering wheel. If you want a true diagnosis, you can go to a rim repair shop (should be a few there on 99) and tell them you want a "trueness check" of all 4 rims. Might cost you a few bucks to get done, but that will tell you if you have a bent rim or not. If you have a bent rim, then you will need to either replace the bent rim(s) or get a new set of rims for the vehicle.

As for checking engine mounts. The easiest check that I can tell you is to get a second person with you. Open the hood of the car and firmly set the e-brake (or place the tires up against a curb or other solid object). Then start the car and have 1 person stand to the side of the engine bay as the other person places their foot firmly on the brake, put the car in gear and then slowly raises the engine RPMs up to about 2,000 RPM. If the engine mount is broken, the person standing next to the engine bay is going to take a few steps back as they are going to think the engine is coming out of the engine bay. You don't want to stomp on the gas in this test as you can break the engine mount. You can repeat this test again, but putting the car in REVERSE. But, normally, the forward check will show the problem.

 

Thanks Thermo, I was mulling my next step and happened to run over a big chunk of I-40 on my way to the grand canyon which blew my tire and bent a rim. I just scored some new OE rims off an 06' so I'm gonna get those mounted today and see if there's a difference.

The more I drive the more I'm thinking it's the driveshaft, it seems to happen after its had a little time to warm up and you can definitely feel the vibes in the center console which is right about where that bearing is.

However, I'll post tomorrow if there's a marked difference with the wheel install tonight.

 

Sorry for the long delay, I finally got the new rims on and it made a big difference. I guess the old ones were pretty messed up from the old lady who drove it before me. The thumping is still there ~30-35ish and then at a higher frequency ~65-75ish.

I went underneath to look at the carrier bearing and there was a little play when I wigged it back and forth. It made the same thumping sound so I think that it is the culprit. It only happens when the car has been running a while so I think its heat induced but I'm curious if the shaft is out of balance, bad carrier bearing, or should I replace the u-joint? The carrier bearing has previously been greased.

 

Millertic, from our experience, if you can see play in the carrier bearing, it needs replaced. As for the U-joints, people have replaced them, but they seem to not be a source of problems. Get the carrier bearing replaced (either new bearing or getting a complete rear driveshaft) and go from there. Unless the U-joint has play in it, I would not worry about the U-joint.