I have a RWD American car and a similar thing happened to it. The whine was caused by bad axle bearings. However you need to find a good mechanic who is expert in the rear diff on your car and get him to check it.
please help diagnose rear end whine
- Thread starter Jim Spahr
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Sounds like the pinion.It may last a long time this way or it may not.You may want to get it checked out.
JHZR2
Staff member
Hi,
car is a 91 BMW 318i, 5speed manual, 4.10 LSD diff, RWD.
The car uses 75w-90 redline fluid, which is the weight specced for it.
I get a pretty annoying whine, seemingly coming from the rear end of the car. What I know is this:
-tends to not occur until car is hot from running (5-10 mins)
-tends to only be noticable above 35-40 MPH in 4th and 5th gear (may be because engine noise muffles it at lower speeds in lower gears).
-throttle dependent: seems to be the worst at throttle that is just enough to maintain constant speed. It I let up on the throttle (while in gear) the noise goes away. It also quiets when I press harder on the accelerator. If I let up on the throttle just enough to barely decelerate, the noise goes 'on and off' I suppose due to slight variations in actual throttle pressure and road flatness.
-No noise when I let up off the throttle or take it out of gear.
-turning does not seem to quiet it much, although it has been hard to test it on the road at 35-45 mph, as I cant steer the car all that hard without veering off the road.
-differential gets pretty hot after highway driving (maybe this is normal?)
-all fluid levels are correct
-had diff rebuilt a while back because fluid was brown and murky. Quieted noise somewhat, but its still there.
So what do you think? Bad diff? Bad rear wheel bearings? Bad transmission?
Any help wouldbe most appreciated.
Thanks very much!
JMH
car is a 91 BMW 318i, 5speed manual, 4.10 LSD diff, RWD.
The car uses 75w-90 redline fluid, which is the weight specced for it.
I get a pretty annoying whine, seemingly coming from the rear end of the car. What I know is this:
-tends to not occur until car is hot from running (5-10 mins)
-tends to only be noticable above 35-40 MPH in 4th and 5th gear (may be because engine noise muffles it at lower speeds in lower gears).
-throttle dependent: seems to be the worst at throttle that is just enough to maintain constant speed. It I let up on the throttle (while in gear) the noise goes away. It also quiets when I press harder on the accelerator. If I let up on the throttle just enough to barely decelerate, the noise goes 'on and off' I suppose due to slight variations in actual throttle pressure and road flatness.
-No noise when I let up off the throttle or take it out of gear.
-turning does not seem to quiet it much, although it has been hard to test it on the road at 35-45 mph, as I cant steer the car all that hard without veering off the road.
-differential gets pretty hot after highway driving (maybe this is normal?)
-all fluid levels are correct
-had diff rebuilt a while back because fluid was brown and murky. Quieted noise somewhat, but its still there.
So what do you think? Bad diff? Bad rear wheel bearings? Bad transmission?
Any help wouldbe most appreciated.
Thanks very much!
JMH
......as you might guess from my name, i own a 92 525i with the 4.10 lsd rear end. are you ABSOLUTELY sure that it is spec'd for 75w90? is that the rebuilder's spec'd oil? i am almost certain that most, if not all of the bmw LSD units from that era require castrol XLS or 75w140 oil. i was beginning to get a little noise similar to what you describe, and a replace with mobil 1 75w90 only amelioriated the problem for about a week before it came back. I replaced it with royal purple 75w140 and a tube of autozone LSD additive. A month later (including vehicle use as a delivery vehicle) and i hear nothing. I'd check your bentley manual and tell us which oil it says you need to use...castrol XLS or XJ.....one is w140 and one is 90. if you had it rebuilt, i doubt that its done so soon in life, unless the rebuilder messed up.
MolaKule
Staff member
1. Replace U-joints if you haven't already done so.
2. Take a fluid sample and do a used oil analysis. Make sure fluid level is sufficient but not over the fill hole.
3. Pinion drive bearing may be wearing out or you may simply need a new shim pack to reload gears. Shims wear and loss of preload at pinion causes clearances to increase between ring gear and pinion drive gear.
2. Take a fluid sample and do a used oil analysis. Make sure fluid level is sufficient but not over the fill hole.
3. Pinion drive bearing may be wearing out or you may simply need a new shim pack to reload gears. Shims wear and loss of preload at pinion causes clearances to increase between ring gear and pinion drive gear.
JHZR2
Staff member
yep, the xw-90 is the correct oil specced for the e30 diffs. However, I am familiar with the use of the xw-140 oil, based upon a TSB regarding differentil noise in some newer models. It suggested only using synthetic xw-140 XJ lube, putting the rest of the convntionl lube that was in stock into the older cars being serviced, and then when stocks ran out, ll cars would be serviced with the 140 weight xj lube.
JMH
JMH
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