"whirrrring" noise from rear

[knotcher]

a little back ground - i'm in the process of building a dedicated e30 track car.

no interior, no sound deadening, replaced everything bushing front and rear, 4.10 diff, brakes, ss lines, rear shock mounts, etc.

i took it for it's first "test" drive yesterday and i get this "whirrring" sound coming from the rear. at low speeds you can notice it change pitch with the rotation of the wheels. it sounds mostly like pads rubbing. my first thought is that it's the parking brake shoes rubbing, but there's no real way to tell without pulling off the hub again and i really don't want to do that. any idea?

also, i know that if you lift the rear end and turn one wheel, then the other turns as well...is there supposed to be a little "play" in that or should both wheels turn in perfect sync. with mine, i have to turn one wheel a couple of degrees before the other will move.

[Rogan]

unless it's spooled rear, there will be play between the wheels.

Mine "whirrs" in the rear, but it's my diff, I do believe.

[jlevie]

You can probably determine if the noise is from the brakes by gently applying the brakes with your left foot while staying on the gas to maintain speed. If the noise disappears as soon as you touch the brakes, it may be the pads. The same trick can be used to rule out the parking brake.

My guess is that the noise is from the tires, differential, or wheel bearings. Once you strip the car you are exposed to all sorts of noises that were previously masked by the sound deadening. Unless the noise is quite loud, it probably isn't anything to worry about. But if the car has significant mileage on it, proactive replacement of the rear wheel bearings is a good idea. That would also be a great time to replace the rear subframe and trailing arm bushings. And a bushing change is virtually a necessity on an E30, just based on age.

[knotcher]

You can probably determine if the noise is from the brakes by gently applying the brakes with your left foot while staying on the gas to maintain speed. If the noise disappears as soon as you touch the brakes, it may be the pads. The same trick can be used to rule out the parking brake.

My guess is that the noise is from the tires, differential, or wheel bearings. Once you strip the car you are exposed to all sorts of noises that were previously masked by the sound deadening. Unless the noise is quite loud, it probably isn't anything to worry about. But if the car has significant mileage on it, proactive replacement of the rear wheel bearings is a good idea. That would also be a great time to replace the rear subframe and trailing arm bushings. And a bushing change is virtually a necessity on an E30, just based on age.

i really don't think it's a case of "it's always made a noise and i just never heard it before". i took the car to a very gentel slope and let it roll in neutral. as soon as you get to a walking pace, you can hear it clear as day. and it changes pitch as the wheels rotate which leads me to believe it's either the pads or bearings.

[jlevie]

Try the trick I described to see if the noise is from the pads.

You'd be surprised at how much difference in noise level gutting the car makes. With no other changes besides mounting a Sparco Evo, my Spec E30 got probably 10 times louder the evening I got all of the interior and sound deadening out. What had been, for an E30, a very quiet car had all manner of whines and other sundry noises on the first drive after gutting the car. Driving a gutted car is a very visceral experience.

[BrewCity11]

Try the trick I described to see if the noise is from the pads.

You'd be surprised at how much difference in noise level gutting the car makes. With no other changes besides mounting a Sparco Evo, my Spec E30 got probably 10 times louder the evening I got all of the interior and sound deadening out. What had been, for an E30, a very quiet car had all manner of whines and other sundry noises on the first drive after gutting the car. Driving a gutted car is a very visceral experience.

Very true.

I'll put money on it that it's just your diff, and it's pretty normal.

[knotcher]

Try the trick I described to see if the noise is from the pads.

You'd be surprised at how much difference in noise level gutting the car makes. With no other changes besides mounting a Sparco Evo, my Spec E30 got probably 10 times louder the evening I got all of the interior and sound deadening out. What had been, for an E30, a very quiet car had all manner of whines and other sundry noises on the first drive after gutting the car. Driving a gutted car is a very visceral experience.

i tried the trick you suggested and the noise remained regardless of wether my foot was on the brake or not...same with the parking brake engaged or not.

so now, i'm thinking it's either the wheel bearing or diff.

[kamotors]

probably the diff my differential whines ,the sound increases with speed.(i also have no sound deadening or back seats.)

edit: my wheels bearings are new, and so is the diff fluid. the differential is silent with the back seats in, so i'm guessing its normal.

[E30_fiend]

First off, your noise in the rear is 90% being caused by bad wheel bearings. A whinning diff is a completely different noise than the noise of bad wheel bearings.

Replace them and like previously stated, replace the subframe and trailing arm bushings while you're in there.


And as for everyone else, no matter what ratio diff you have it should not whine. If it does that means the diff is struggling. Drop the old fluid out of there and fill it with redline synthetic diff oil with the limited slip additive. Most likely your diff is making noise because the oil in it wasn't LSD specific. So just grab some redline and throw it in there but make sure it gas the additive.







Taylor

[knotcher]

First off, your noise in the rear is 90% being caused by bad wheel bearings. A whinning diff is a completely different noise than the noise of bad wheel bearings.

Replace them and like previously stated, replace the subframe and trailing arm bushings while you're in there.


And as for everyone else, no matter what ratio diff you have it should not whine. If it does that means the diff is struggling. Drop the old fluid out of there and fill it with redline synthetic diff oil with the limited slip additive. Most likely your diff is making noise because the oil in it wasn't LSD specific. So just grab some redline and throw it in there but make sure it gas the additive.







Taylor

i'm leaning in this direction as well...i really don't think it's the diff. i'm going to have some friends drive it and see what they think.

btw, all bushings in the rear end (rtab, subframe, diff) have been replaced with poly.

[jlevie]

While using the wrong fluid can cause whine from the differential, wear in the gears and bearings will cause noise even when the correct fluid is used. In most cases, whine from the diff is caused by wear on the gears.

Not using a friction modifier in a limited slip differential shouldn't cause noise except when the car is turning. As long as the car is traveling in a straight line (and you aren't exceeding the tire limit) the clutches aren't slipping and thus the friction modifiers don't come into play.

[Uber E30]

Easy way to test the wheel bearings is to find a nice big parking lot. Drive around in a clockwise circle at a decent speed and then change to a counter clockwise circle. If the noise changes then you know for sure its the wheel bearing. Putting more(or less) weight/stress on one side generally changes the pitch of it.

You can also have someone else drive your car and you sit in the back. See if you can pinpoint what side the noise is loudest on or if it comes from the middle. Left or right would be wheel bearing, middle would be diff. Wheel bearings also sound like a really loud humming while diff usually sound like a high pitched whine.

[ieatpeople]

i thought i needed rear wheel bearings, until i changed my diff fluid, the p.o. had some regular fluid in it, i replaced that with fluid specifically for lsd diff's and the noise went away instantly.

[knotcher]

just to update...it was the wheel bearing...i had it changed out and the noise is gone.