At my wits end with driveshaft vibration

[stargazer_61]

Well, as the title says...

A few months ago, I replaced a shredded center bearing, in similar condition to what Jon K posted, due to knocking in low speeds/gears. Vibration didn't go away, but was reduced. So I replaced collapsed engine & trans mounts, but that didn't do it either. So I babied the car until I could get the time to redo the center bearing & guibo. In the process of babying, I broke another center bearing. Anyway...

Yesterday I finally replaced the guibo & center bearing. Took the driveshaft to the BMW dealer in Chapel Hill to have them look at the U & CV joint. Tech thought they were okay - U was smooth with no notchiness, and no noises in the CV (he called it "tinging"). Got the car back together & took it out to a little used road with twisties. Slight vibe around 20 mph, but no banging at 30-35. Yay! So I really exercised it for the first time in months, sport mode, flooring it, 70mph through 35mph turns, smooooth...

Parked the car for an hour. Left the house to go pick up my daugher at work. At 20mph, I hear knocking. Argh!!! Lots of low speed vibration now. What have I done or forgotten to do?

FYI, the old guibo was pretty mushy. Lots of fractures, but not shredded. New one is rather stiff. I did not preload the bearing. I allowed it to "settle", then tightened it down. I believe that it is installed the correct way, and the driveshaft was marked to properly reassemble it. I did not mark the diff or trans flange to put the driveshaft back in the same holes. Would this make a difference?

[joshua43214]

Marking the flanges should not have been needed, I always do just to be safe, but I am anal about some things. Some people have been posting lately about getting bad OEM guibo's out of the box, seems they are hard as a rock and do ot flex the way they are supposed to, maybe you have one of these?

Can you tell where the noise is coing from? sometmes driving down an alleyway with building crowded on both sides can help locate noises. Try driving with the windows up and the windows down, rear window up/down etc. If it makes noise inside at 20mph, there is a good chance you can hear it at 10mph or so if you are in a narrow alley.

An out of balance drive shaft should not vibrate until higher speed, low speed vibration is a sign of binding. Might be worth double checking the carrier bearing is aligned properly. Also make sure its faceing the right way, the mount can be put on backwards.

[Bellicose Right Winger]

Interesting that you didn't have any problems upon reassembly, but only after the 1 hour "hot soak". I think this rules out the stiffness of guibo being the problem. Exhaust and catalyst heat rises and cooks the drive shaft after a driven car sits, particularly if the heat shield is damaged or missing. I'd try to preload the center bearing, it's the seems to be the only thing that could be improved upon. I doubt it's installed backwards as it's mounting flanges are different lengths and drivesahft would be noticeably offset if it were. Is vibration still present after car has been sitting overnight, letting everything cool off?

Paul Shovestul

[Derek A.]

1. Output shaft bushing in transmission is shot ??
2. Driveshaft itself is out of balance.
3. Maybe you are feeling a number of different things - wheel tire & driveshaft ?

[stargazer_61]

To answer some of your questions:

Right now, it is a thumping. It is definitely coming from the d/s tunnel. It is definitely at low speed.

I am not sure about cool down reducing it. Right now it is up in the air, all four wheels, and the exhaust is off, so I can see what is going on. It feels solid, the carrier bearing did not break (again).

The input shaft bushing was worn, but two stealers did not have the part available. I put it back together anyway.

Wheel & tire balance appear to be good. At speed on smooth roads it feels fine. Was last balanced on a Hunter.

Prior to removing the exhausts, I ran it with the rear wheels off the ground. I can feel the vibration, though at a higher indicated speed, leading me to believe that due to less torque being required to turn the wheels, the vibe requires higher speed to come in.

[joshua43214]

I doubt it's installed backwards as it's mounting flanges are different lengths and drivesahft would be noticeably offset if it were.
Paul Shovestul

This was my point exactly, the offset is not so noticeable when the car is on jacks, and even if its on a lift, it can be overlooked. We had a person recently on the board do exactly this not long ago.

I am also a bit concerned about the carrier bearing breaking after a replacement, did you ever determine the cause the the last bearing failure?

[stargazer_61]

I have no idea why it broke. I suspect it was the guibo, which was quite weak, so I replaced that as well.

Here is an update to what I have since discovered:

The bearing is indeed on with the correct orientation. The d/s is straight. Ran the car up to about 60mph on the jacks, noticeable vibration. Had the wife run it up while I crawled underneath of it. D/s does not vibrate and is not off center - I put my hand on it while it was turning at the trans, both sides of the carrier bearing, and at the diff. Smooth, virtually zero axial deviation.

However, the left rear axle was bouncing quite a bit. I put a floor jack underneath the control arm and raised it up a bit. Vibration was less, but still present. Then I noticed a lump in the tire, on the inside sidewall. Looks like I blew out a belt whilst thrashing it yesterday. Tire is worn in the typical, inside tread location, and the balance has obviously been thrown off.

The conclusion is that my d/s vibration should be cured, but I need new tires for the rear.

Thanks all for the assistance.

[stargazer_61]

Well, the vibration still is not cured. However, I believe that the vibration may be related to the rear end. Occurance is at low speeds, up to 25 mph, then is gone. The noise is a thunking along with the shake. Prior to changing the carrier bearing & guibo, it would vibrate up to 45 mph.

Had a look at my pitman arms. The bushings are completely compressed and practically gone. Also, the rear control arm bushings on the driver side appear to be goners as well. It could be dirt and crud, I will have to clean it up to be sure. Passenger side bushings look okay. Subframes as well look okay, but it is hard to tell without removing the arms that are bolted to them.

The only time I don't get any vibrations in the car is when it is up in the air and the rear tires are off. The bad tire is now in the trunk and the spare is on. Any other suggestions before I take it into the shop?

[632 Regal]

2 piece driveshaft? If you seperated it the axial of the 2 could be off causing binding noticable at lower rpms.

[joshua43214]

My thoughts are that if the vibration goes away when the vehicle is raised, it means something is not positioned properly to run at ride hight.

Since you have had an unexplained carrier bearing failure, and what sounds to me like drive shaft binding now, I would be suspiciouse of the positioning of the carrier bearing or the plunge joint. You did mount the carrier with the car flat on the ground?