Tiny vibrations from rear axle

pmansson

pmansson

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Today I suddenly got/felt small vibrations at around 50 MPH. It seems to stem from the rear end. It is not the wheels and it disappears at speeds over 70 MPH.
Anybody experienced this before? Wheel bearings and rubber bushes are newly changed or checked. Propshaft was balanced when shortened for 5-speed conversion 2 years ago. Brakes are new. Could it be the differential unit with its bearings and other moving parts? Or the driveshafts?
I appreciate all ideas and suggestions for further investigation.
 
Couple of things I can think of....

1...Check the run out on the rear disks (side to side wobble) they are quite sensitive to this. Use a dial gauge to check. Even new disks need a flat surface to mount to
2...Handbrake shoes new/adjusted correctly?
3...Shock absorber top/bottom mounting bushes ok?
4... ALL subframe bushes good?
5... Check shafts for split rubber boots, "dry" cv joints
6... Wheels balanced? look for "lost" weights
7... Uneven tyre wear, under or over inflated?
8... Uneven tyre wear, rear trailing arm alignment out?
9... Too much "stuff" in the boot (Trunk)
10.. Prop shaft center bearing failing
11.. Guibo "donut" at the gearbox going
12.. Condition of rear brake flex hoses if old may be swelling internally.


Oops :oops: more than a couple of things but stuff I would check
Malc
 
small vibration--will likely grow with time

what I suspect--you mention the drive shaft was shortened and re-balanced when 5 speed was installed--

Did you have the U-joints replaced? Apart from a bad guibo or failing center bearing my experience has led to this problem--that after many years of service the so called permanent lube gives up and the U-Joints start binding as they turn creating a mild vibration that will gradually increase in intensity and will ultimately fail if not addressed. Have them checked in the air with no load on the drive shaft--if its the problem it will be noticable
 
U-joints checked, new guibo, new centre bearing and problem persists between 50-100 km/h. In fact worse as the new BMW guibo is firmer that the GM guibo that was mounted previously. A garagist thinks the alignment of the engine/box and prop shaft is incorrect. He wants to lower the exhaust system and lower the propshaft to see what the "natural line" is. I use the yellow engine and gearbox mounts from Ireland Engineering since 2 years (one for gearbox where garagist want to mount the other side polyeurethane bush as well). On the new guibo one can see that the pressure from the propshaft pushes the guibo sort of sideways.
I´ll come back on Tuesday and update on the issue.
 
undiagnosed vibration/s

If your driveline is somehow askew, this may be the source of your vibration/s. From my limited experience, urethane mounts tend to accentuate/exacerbate vibration/s that would usually be less discernible when using much softer rubber mounts. Of course, everything has its limits, including rubber mounts and if this were a perfect world and your drive line were perfectly straight and balanced rubber/urethane mounts would be unnecessary.

Tangentially, I have had mounts (both rubber and urethane) look perfectly good only to find the rubber/urethane cracked or severed from the metal to which it was designed to adhere. I recently had this happen with a transmission mount. While I had no vibration issue, I was shaking the exhaust system and was amazed to see light between the yellow urethane and the metal post to which it was supposedly stuck. Go figure!

I am curious as to your use of a "GM guibo." Are you saying the General Motors makes a guibo that fits the E9? What model GM vehicle/s does that part fit?

FWIW, over the years I have had my share of driveline issues (not with E9) although I switched from the solid rubber guibo to the laminated version found on some automatics and later big six models. I made the switch after going to the trouble of installing a newer one only to have it disintegrate within a couple of days. I would agree that the solid rubber may be more forgiving in terms of its shock absorption, but the laminated version seems to last a heap longer.

Somewhat related, I remember a driveline vibration problem that I spent countless hours trying to diagnose with a series of hose clamps over the driveshaft. It seemed that everytime we thought everything looked smooth and balanced under the car, a test drive proved us wrong. It wasn't till I removed the shaft to re-re-examine the u-joints that I discovered one of the tackwelded weights was loose. I surmised that the weight (looked like a flat plate) would lift off the shaft at high speed (due to centrifugal force and/or air resistance). Retacked the weight, removed all other balancing apparatus and the problem disappeared.

Good luck. Please keep us posted. :lol:
 
I was just about to suggest this when I read bengal taigas post, check that the tack welded balance weights are still there! They do sometimes come off.
 
I had this problem with my E39 for several years. Vibration in the rear of the car around 50-60 and gone at 70. I took it to the dealer and they said don't worry - it's only a bent rim but it is well within spec, ... right. I finally decided to get new tires and I had them move the rear rims to the front and vice versa. but the problem persisted! I asked myself, "self, how could this be? if a rim was bent the vibration should have moved to the front!" It couldn't be an out of balance wheel or anything that simple because I just had new tires installed and balanced! After another month and lots of visual inspections I went to another tire place and asked them to double check the balance even though I knew better. All wheels were off more than 1/2 to 3/4oz! After the re-balance my vibrationproblem is gone and hasn't come back.

Since your problem seems to go away above 70 it rules out quite a few things (guibo, center bearing, u-joints and the like generally get worse with speed). Wheel balance, however, is not ruled out. Sudden appearance of the problem could be because a wheel weight was thrown.

My point is that while there are plenty of exotic possibilities for the source of your vibration, the pedestrian process of having your tires balanced could be the simple solution and it doesn't cost very much. :roll:
 
Short update: my mechanic noted that the driveline was not entirely straight. He has inserted a couple of shims on the front engine mounts to get a straighter line from engine to final drive.
We now have the strange situation where WHEN COLD, the vibrations are very clear around 50 MPH, but 10 minutes later, when the car is WARM, they disappear (almost completely). An interim stage was with a new guibo, the problem increased (with the stiff, new rubber we presume).
I´m about to get hold of another propshaft and change the U-joints and have it balanced.
I´ll continue as we progress.
 
more superficial analysis

My analysis is seat of the pants, but when you mention temperature and driveline, the first thing that comes to mind is lubrication. The e9 driveline has a center support "bearing," a u joints, and a sliding/telescoping of driveshaft.

The center support bearing could be wanting for lubrication or the rubber may be too relaxed so that it permits more movement (vibration) than ordinarily tolerable.

A poorly lubricated u-joint may also contribute to the symptoms you describe and the quickest means of determining this issue might be to physically rotate the joint or the two shafts which are connected by the joint. Smooth action= move to different part.

The telescoping driveshaft has a locking collar that should inhibit most movement. Perhaps the shaft splines are dry or poorly greased, or the locking collar is worn, loose or bent.

I would expect that if you have gone to the trouble of replacing a guibo, you or your mechanic would have been able to visually examine the driveline through its normal range of motion and sight the area of most vibration.

FWIW, your mention of a GM guibo piqued my curiosity. I am informed it may be from a Cadillac Catera. I am not familiar with it, but wonder if it isn't the same as used by Opel and BMW. I am no expert, nor anywhere close to being an expert, but I find it difficult to accept that a soft guibo (GM) would provide more vibration than a harder one. In fact, I would expect just the opposite.

Good luck and keep us posted.
 
Centre support bearing has been changed. U-joints have been checked (and are just 2 years old).
The old guibo had GM stamped in profile on the rubber. We beleive that it is softer than the BMW one, and explains why the problem increased with the new guibo.
There is a certain rubber/clutch smell around the car as well....
Strange too, that the problem came all of a sudden, rather than gradually.
I might exchange the final drive too, as I have a newly refurbished 3,45 LSD awaiting installation.
Sooner or later we will identify the culprit, which I will gladly share with you all.
 
The center support bearing could still be the cause. They will make a terrible racket when they have even a slight pit. You'll normally notice the noise near the parking brake; it may even be possible to feel when you touch the area. The input and output shaft bearings on the transmission are also noisy when they are even modestly pitted. My input shaft bearing is starting to go; it is noisy when the clutch is engaged only (even in neutral).

Even though your center support bearing is only 2 years old is it possible that it was 35+ year old NOS? If so, this "sealed" bearing could have some very old grease. When it heats up the old grease may start to work a bit.
 
Noise is not my problem. It is physical vibrations at 30-50 MPH range when car is cold. We are going to check for lost balanceweights on prop shaft, or i might just get another one prepared and exchange them. That will take care of possible U-joint issues.
 
Hi - I have just had a similar problem..symptoms not identical but maybe worth considering. Also experienced a vibration present at idle and most noticeable at 30mph but would become less obvious but not disappear as speed increased over 30mph. One of the metal straps holding the pressure plate had busted and caused the plate to shift off centre causing the vibration. The mechanics had considered all the other potential causes as per your investigations and correctly(eventually) identified my problem..worth a thought.
 
Finally solved

Yesterday I drove the car to the garage where a newly balanced propshaft with new U joint and bearing was awaiting mounting. As I drove the old problem of imbalance at 30-50 MPH was still present, esp in the beginning. At 70 MPH on the motorway it was almost gone.
After dismounting the existing propshaft it was discovered that the guys in another garage, 3 years ago, had mated the two parts 180 degree wrong. The strange thing is that there was no imbalance for the first 2 years, totalling 3,000 miles. Then it suddenly appeared, with some sort of noise from the rear or bottom somewhere.
Now the first prop shaft will be rebalanced and its U-joint exchanged. Nice to have when changing another car to a 5-speed, enabling the work to be done in one go, rather than wait a week for prop shaft work elsewhere.
 
Interesting thread, I was just having this problem myself.

I finally got my car running (except for some hydraulics issues, waiting for a new brake bomb) and am getting heavy vibrations at some speeds.

Looked beneath the car and there is a big dent in big outer ring of the support bearing.

Have no idea how that got there, car has not been driven since it worked before. New one ordered so I hope it is that. Otherwise I will use the other tips.

/Johan
 
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