Mad vibrations!
 

So I went to take the car out today after being in its usual hiding place for 2-3 weeks. About halfway in my drive I started getting bad vibrations. It is fine at low speeds but around the 30-35mph mark up to 55mph (never went higher).

You know those rumble strips on the highway that let you know to WAKE UP and get back on the road? Kind of like that but less violent. I am 95% sure it was a weight that flew off either the rear wheels or maybe the driveshaft. I haven't gone home yet to check, but that is something I can check on tomorrow.

I have narrowed it down to 3 things:

1. Wheel weight Fell off of rear wheel
2. Weight fell off Driveshaft
3. Driveshaft U joints starting to give the ghost

I will check it out tomorrow, but wanted some insight on this. My bearings are all within 2 years new so Those are not high on the list...

I can tell you that if you throw a retainer ring on a u-joint and one of the bearings flies off you will most certainly know about it lol. When in doubt GO FASTER!!!

Serious note - Probably a wheel weight.

Edit: Does the seat shake?

Yes the seat shakes the most, so I know it would be related to the rear.

If I push the clutch in it gets worse, then I let it out, it shimmies less... but still horribly so.

Just using the cl;utch may indicate it's driveshaft related. The shaft keeps turning as long as the wheels are, but pushing the clutch in unloads the driveshaft. That's where I would start.

You know i had the same situation...push in the clutch at highway speeds and the vibration occured.

I checked the driveshaft, u-bolts, tire weights, all good..

Then someone on this forum told me to check the rear transmission mount. I pulled it out and it looked OK...I replaced it anyhow and this solved the problem. I guess the old mount was weak.

So the car is now on jack stands. I looked over the weights and every one was still there.

I noticed on the driveshaft near the top there is a bar weight on it, then right beside it there seems to be what looks like 2 tack welds that used to hold something on there.

Good call on the transmission mounts. I was going to replace the engine and trans mounts with solids, I guess now is a better time than any to do so.

let us know if that solves the problem!

i would suspect either the rear u-joint or the trans mount. there is a weight on the driveshaft that keeps it balanced, much like a wheel weight. have you checked tire pressure? sounds more like the other things mentioned but it wouldnt hurt to check.

Finally got around to checking the trans mount. I pulled it down and off today, looks to be in great shape. No cracks or anything, looks new:

http://i25.tinypic.com/33avrkl.jpg
http://i32.tinypic.com/fxfcbt.jpg

Going to check the U-Joints next.

keep us posted. the u-joints are commonly prone to failure.. however, for being 20+ years old, they really hold up well.

Funny thing is..my trans mount looked new also!

Put the mount back in and went to check the driveshaft U joints. They were all good, but the surprising thing was I am missing a bolt! Plus 2 were bolted down tight, and the 3rd was hand loose. I tightened them all back down, but I am still missing one bolt.

Took her out for a drive, and saw a S4 TII :D

She is all fixed. I guess the loose bolt did it?

Always the simple things, huh? Someone probably forgot to tighten them down last time or maybe the threads are shot on the hole with the missing bolt. Did you get the missing bolt replaced?

No, I think it's gone in the wind. She drives fine with 3 bolts, but if I run across another I will be throwin it in :)

Sucks it was that easy.

Baby Jeezus (sorry, I couldn't resist);

Get that 4th bolt replaced, willya? This whole thing is about a 'balanced' system, and that bolt is part of that system aside from the fact that it also helps to carry TORQUE from your ENGINE to the wheels, you don't want to be broken down at the side of the road because you figured 3 was good enough, when it's designed for 4 bolts.

Worst case, the 3 remaining bolts shear off as you're going around a sweeping turn, the driveshaft flies out the back of your car, and the sudden loss of power to the rear tires causes you to skid off the road, down an embankment, and into a bus load of nuns on their way to feed the homeless.

There, did I give you enough to think about? (You've gone quiet because you're out there putting the 4th bolt in, right...???)

Just a question, as I have slight vibrations, not violent like that but... Did the vibrations get more noticeable as the speed increased? Mine are most noticeable at 60-70 but seemed to diminish at about 90. Were you saying your vibrations disapeared after 55mph in your case?

Driveshafts, like wheels, are balanced at a certain speed. They can, however, vibrate at other speeds, depending on the harmonics.