Help! Grind/scrape/grab 20-0 & 0-20 mph

[E3Owner]

Hello all,

Been doing lots of searching but I can't figure out what is happening. E30 vert has a grind/scrape/grab (for lack of better words) while normal braking that starts at about 20 to 0 mph and then again from 0 to about 20 mph. The noise is not constant, it is a grind/scrape/grab once every revolution of the wheels. It seems to be coming from the rear. It seems to stop after about 20 mph. Here is what I've done to try to figure it out/remedy:

- Hard braking - It doesn't grind/scrape/crunch
- Hard acceleration from 0 - Does it for a split sec and then disappears
- Swerved left/right while grind/scrape/crunch is happening - No change
- Jacked car and rotated wheels - No perceivable noise other than faint differential gears rotating and light brake pad noise
- Cleaned calipers and ensure pistons are free( cleaned slide pins, caliper piston, cleaned and greased pad contact areas) - No change
- Replaced both rear rotors (used same brake pads cause they where new) - No change
- Checked and adjusted ebrake - No change
- Checked for evidence of rubbing on dust plates, parking drum back plates, caliper and old disks and found nothing
- There is no clicking sound or evidence of wheel bearing or CV join problem
- There is no steering wheel shake or shimmy. There is however a slight vibration I can feel in the seat of my pants.
- Straight line braking is perfect
- Alignment could be better but is not bad as it is
- Tires are wearing evenly


I'm stumped and need you guy's help if you care to chime in. Perhaps some of you have encounter this problem before.

Here is what I'm thinking
Maybe bent wheel hub? But wouldn't that manifest itself at any speed?
Maybe a bad wheel bearing? But that is typically described as a humm and it is constant and changes with load?
The right axle is leaking grease (strange because the grease is right where the axle splines go into the wheel hub and the rubber boot does no seem to reach there ) Could this have anything to do with it?
Could it be a carrier bearing in the diff (there is no humming or any sound from the differential while driving, coasting or under load)
Could a drive shaft bearing exhibit these symptoms?
The suspension is in need of refreshing (it is a 23 year old car after all)

Anyways, as you can see I'm loosing my mind. Any help figuring this out is greatly appreciated. Thanks a bunch.

[superj]

does the input gear (I don't know the exact terminology) of the diff move when you wiggle the driveshaft right in front of the diff?

[E3Owner]

I think I got what you are saying. I don't know what it is called either I guess differential input shaft? No I did not check for drive shaft movement, just assumed any lateral play there would manifest itself at any speed and under load but I will check it and report back, thanks. If it were the case what does it mean and what's it doing to create the problem?

[Seawolf]

Pinion

http://www.ebay.com/itm/BMW-E30-168mm-Differential-3-45-Ratio-Ring-amp-Pinion-Gear-Set-Small-Case-LSD-/360446654267

Edit: What shape is your parking brake in ? It's possible that something is broken and floating around in the drum.

[E3Owner]

I cleaned and adjusted parking brake. It's good. There isn't much play in the gears which leads me to believe gear spacing is within specs. Also to answer a prior suggestion, I checked the drive shaft and there is no lateral play at the input shaft or the center bearing.

Again, the grind happens every rotation of the wheel so it increases with speed. On deceleration it starts around 20 mph until 0 (full stop) and on acceleration it starts from 0 and stops around 20 mph.

[E3Owner]

Bump! Anyone?

[Ksbsn88]

Rear subframe bushings or lower control arm bushings? Wheel weight hitting brakes when brakes are applied?

[E3Owner]

I'll take a look at that thanks. I'd hoped someone may have encountered the same/similar issue and found or can point to a definitive cause. Evidently no one else has. I don't like to leave loose ends so as a last post, there isn't enough experience and the issue remains unsolved. Thank you all for your input.