Differential noise or center support?

[632 Regal]

Just noticed a new noise. Basic description would sound like a snow tire on a bent rim but only starts at 20mph and more so on deceleration. Can hear it more after it warms up, not loud, faint but there.

I thought it was the differential but the fluid is perfectly clear with no metal at all. I swapped this into the new ride and had to replace the input flange and fresh fluid. At the time the pinion did have a slight unhappy bearing feel to it. Drove it 5000 miles since in city and on several long highway trips (+500 miles) and no issues. I still worry.

This car always did have a driveshaft imbalance type vibration which mostly went away with the 3:64. I would guess differential bearing but it is not constant IE the description of snow tire on bent rim. It's like a howling that warbles... wu wu wu wu wu real fast. I doubt the wheel bearings or cv joints, this noise is too fast.

If it was the differential I would guess it wouldn't warble and be more constant. At the present time I am unable to do more trouble shooting due to all my stuff is still holding my sons car in the air.

I am also thinking a tire since these are about half way done but to notice it this sudden makes me wonder.

Been searching all day and come to the next question I just can't find an answer to:

Is it possible for a center support bearing to make this type of noise?

[Rustam]

If the membrane holding the bearing has been torn around the curcumference, then its conceivable that the rubber on the fully turning bearing brushing against the left over in the band can give this noise. It's likely this is the problem, especially considering the noise is "fast".

The membrane can be pretty thin allowing a rip around the bearing. Last time I replaced the unit, I filled it with silicone all around between the bearing and the band, on both sides.

[mattyb]

had a centre bearing go years ago. does it sound like a squeaking noise? dry perhaps? starts at 20 or so but goes at about 40+ and at speed. centre bearing first stop in my opinion

[shogun]

Best is you check all driveline parts starting from the engine rubber mounting, universal joint/giubo (if installed, not all have it), center bearing and also the trans mounts, it must be all in one line from front to rear, these are all wear parts. I have seen trans mounts where the rubber had completely separated from the bolts. Engine mounts about the height of 2/3 of a new one, +20 years of 200-300 kgs of engine weight on the rubber mounts cause this.

We had a few years back a similar problem on a E32 740iA .
There was a clearly noticeable vibration in the drive train at about 1200 to 1400 RPM + at 1800-2100 RPM . Vibration especially when accelerating. Under hard acceleration sometimes the drive shaft joint hit under the body. Especially when engine/trans was cold (like on cold mornings when the car was parked overnight) the vibration occured more than when all was at operating conditions/temperatures . New parts were already installed : engine mounts, transmission mounts , center bearing , constant velocity joint/giubo , the driveshaft had been fine balanced by a specialized shop for drive shafts remanufacturing , beer cans on rear axle , dogbones, etc pp ......
Transmission in perfect order, switching smooth without shocks thru all gears.

The following was done : it was noticed that the fully reman trans with new trans mounts MOVED, motor mounts were also new, it moved sideways , for example with the short original car jack lever one could move the trans 20mm sideways . Engine and transmission have a total weight of about 300kg , that is a LOT of vibrating mass . So we used an old lead - pole terminal and bent it to an angle and screwed it into one of the many existing unused weld-on nuts in the transmission tunnel. Then a test drive with a few kick-down starts, simulated moose/elk test + again on the car lift . We found: the angle was at a distance of about 7mm to the transmission. Then we welded for a test two brackets and used the "old" transmission mounts (2 years old ), installed instead of the screw the bracket to the exhaust system , i.e. , the transmission was now supported on both sides by two additional transmission 'mounts' bolted in two existing weld nuts. New test drives: all noises/vibrations gone at all tested speeds and RPMs, no vibrations when starting to drive as before. Apparently -what we believe- the Shore hardness of the trans mounts is not correct, although original from the 'friendly' dealer shop. Since the mounts look like standard machine beds , we suspect that at some point a purchaser at the purchasing department in the factory has ordered the mounts just from the catalog because he did not get anymore or it was difficult to get/find the original specification sheets from this old model. That would also explain why the first/original trans mounts worked perfect and had a lifespan of 14 years , but then mounts bought later were deformed already after about two years that they had to be replaced again and again. And when the transmission moves sideways, there is no way that the propeller shaft can work vibration free . All parts installed were original parts bought from the dealer, not aftermarket.

And that is not an isolated case , this here is another attempt to find a cause already in 2007 on an E32 750

"Here's my temporary "fix" ": View of chassis end of cable, attached to right rear trans X-member bolt. http://www.bimmerboard.com/members/erwin/original/trans_cable1.jpg
Transmission end of cable, attached to right exhaust mount bolt. http://www.bimmerboard.com/members/erwin/original/trans_cable2.jpg
Cable getting ready to be re-tightened. http://www.bimmerboard.com/members/erwin/original/trans_cable5.jpg

[whiskychaser]

On the face of it, you were better off going to a scrap yard and getting some 10 year old trans mounts than buying new from BMW? I am amazed. You go to the dealer because you want best quality parts - you can get junk anywhere.

[632 Regal]

had a centre bearing go years ago. does it sound like a squeaking noise? dry perhaps? starts at 20 or so but goes at about 40+ and at speed. centre bearing first stop in my opinion

Not a dry squealing, a whirring with an oscillating frequency.

[632 Regal]

If the membrane holding the bearing has been torn around the curcumference, then its conceivable that the rubber on the fully turning bearing brushing against the left over in the band can give this noise. It's likely this is the problem, especially considering the noise is "fast".

The membrane can be pretty thin allowing a rip around the bearing. Last time I replaced the unit, I filled it with silicone all around between the bearing and the band, on both sides.

That goes along with my theory, at first a dry differential would explain it but that was full. Soon as I can get it into the air I will check everything and replace things. Hoping it doesn't get worse.