Differential Woes (E30 325is)

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epj3

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Alright, sinceI discovered that my CV joints are fine, I figured out that my Differential is the problem (the grinding/scraping/clicking in slow turns)

I saw that my output seals are bad (leaky) and figured the fulid level would be low -- since the seals are quite obviously leaking. When I took the differential filler bolt, gear lubricant started to drip out!! So it's full.

The thing about the fluid, is that it smelled like a combination of propane and burning rubber - the burning rubber smells was so evident that it almost made me sick (and i'm a guy -- we all love the smell of burning rubber... it was quite bad!!) I read on a chevy truck forum that lubricant from a differential that smells like burnt rubber /propane means it was probably overheated.

What do you think it is? I'm going to drain and refill the differential tomorrow - if the fluid was overheated it could have broken down. Since it's limited slip, I can imagine the clutches inside make it quite hot if pushed enough.

Any suggestions, tips, or thoughts? I dont really have the money to replace a limited slip differential. I wouldnt have a big problem rebuilding it if it came down to it -- but I think the cost will be absurd.
 
jrt67ss350

jrt67ss350

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Well, just a tip that you probably know already, but be sure to get fluid that has limited slip additive, or it'll be even noisier after you change the fluid.

Are you sure the fluid smells abnormal? I don't know if you've ever smelled used differential oil before, but normal used differential oil is one of the stinkiest, most pungent, horrible smelling things I've encountered. If you get it on your hands, be sure to keep your hands away from your head or hair. If you get any in your hair, you'll be smelling it for days, no matter how much you wash it. Don't ask me how I know that! [:D]
 
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epj3

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jrt67ss350 said:
Well, just a tip that you probably know already, but be sure to get fluid that has limited slip additive, or it'll be even noisier after you change the fluid.

Are you sure the fluid smells abnormal? I don't know if you've ever smelled used differential oil before, but normal used differential oil is one of the stinkiest, most pungent, horrible smelling things I've encountered. If you get it on your hands, be sure to keep your hands away from your head or hair. If you get any in your hair, you'll be smelling it for days, no matter how much you wash it. Don't ask me how I know that! [:D]
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Yea I had a bottle of Mobile Synthetic fluid which is what's in there now. I didnt get any noises until a week ago, so I'm hoping its just bad fluid.

It is very pungent! The smell made me feel sick and it was all over my hands. Thank god for lava soap [;)]
 
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epj3

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Ugh, I dont really have the money OR resources to replace a differential. Any way to save it?

I still cant figure out out i can have a leaky differential, but still have enough fluid in it?
 
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epj3

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Alright I replaced the fluid, and still have the sound :-/

The old fluid was thick dark black -- I couldnt see the beam from a 3 million candle power spot light through it.

Put new synthetic mobile fluid in it, and it is definitely smoother -- I'm positive it's much smoother -- but I still get the noise when making turns slowly.

I think the clutches in the differential are worn. Any ideas?
 
jrt67ss350

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Well, if the clutches are worn, you can either just deal with it or fix it. I don't know if these cars used non-replaceable cone clutches or rebuildable disc-type clutches. If they used the disc-type clutches, then you can remove the differential carrier from the rear end and then replace the clutches yourself. It'll take some work, but you seem to be pretty technically inclined, so it should be a job you can do yourself. If these differentials used cone clutches, then they aren't replaceable and you have to replace the carrier. If this sounds like too much work, you can swap out another differential (if you can find a limited slip around) and hope that it isn't worn out also, or you can just deal with it and drive it anyways. If it's just the clutches that are worn, then it won't affect the ability of the differential to work, you just won't have limited slip.

If you do a burnout or spin the tires in the rain or snow or whatnot, do both rear wheels turn? If they don't, then the clutches are worn. If they do, then it isn't your clutches.
 
Kirby

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Regarding the rear end oil, are you seeing actual drops of oil, or just the "spray" of oil on the underside of the car? If it's just a film of oil, it's much less to be worried about. This means it is very slowly working past the seal only when the vehicle is moving, and it makes a big messy oil slick from VERY little fluid (not even a milliliter), and it is not dripping continuously. That would explain why it was full when you checked it. You could actually live with this for quite a while. I had this issue with a diff drive shaft bad seal. Over a year I never added any fluid at all.

I'm also thinking that you could live with the mechanical problem for a while. It sounds noisy and annoying, but I think there's no dangerous or catastrophic failure coming up. It will just slowly get worse, just take it easy - no racing or burnouts. Drain some oil once a month to look for debris. Maybe you can live with it and save up a few bucks for 6 months until you can fix it?
 
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epj3

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It's just a buildup of oil and dirt around the axel seal (mostly the passenger side), and it looks like it might be enough to drip now and then but not too bad.

and jrt67ss350, you can definitely tell both wheels are spinning (ie the differential works fine). Say I make a turn on wet pavement and give it some power, you can hear a wheel "skipping" to catch up (which I've heard is normal becuase a limited slip cant allow one wheel to COMPLETELY break loose of the other wheel when there is enough power going to it)

You can feel that it works, becuase i never have 1 wheel just sit there and spin like crazy.

One thing that crossed my mind is that the center support bearing (which definitely needs replaced -- already have it, just waiting to see if i need to replace my exhaust before i try to remove my current rusty exhaust and put ti back together) might cause the driveshaft to cause these scraping/grinding noises. I'll get that replaced in may, when inspection comes up and I find out if I have to replace the exhaust.

I was very relieved to see that the CV joints were okay -- they would be more expensive to replace than an entire rebuilt differential (if thats even the problem).
 
jrt67ss350

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Kirby, I think that's some great advice.

epj, glad to hear that everything sounds like it is functionally working like it is supposed to. I agree with Kirby - I think that this should be something that you can live with for quite a while. I'd just periodically keep an eye on it.

It'll be interesting to see if your driveshaft center bearing is the true culprit of the problem - driveshaft problems can definitely manifest themselves in strange ways and cause all sorts of noises, especially in cars that have slide joints and ones like ours that have fixed support bearings.
 
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