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E36 M3 (1992-1999) {Euro - S50 B32 321hp @ 7400 rpm} {U.S. - S52 B32 240 hp @ 6000 rpm}
Total Produced: 71,212 - Years Produced: 1992 to 1999


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Old Thu, Feb-16-2017, 05:49:17 PM   #21
M3n00b
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Default Re: Leaking Rear Differential That Pops/Grinds/Cracks????

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Originally Posted by fiveightandten View Post
^what he said.

The Allen bolts have been known to back out. Drain the fluid into a clean container and run magnet through it to see if you pick anything up. Pull the cover off to have a look. Check the speed sensor for any large pieces of metal stuck to it, and have a look at all the fasteners inside to make sure they're there.

Though, honestly, if you see anything questionable, I'd just replace the diff. They're cheap enough used and it takes an hour to do.
This is what happened to mine at 75k mi. Good old royal purple. My current diff has red line in it.
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Old Thu, Feb-16-2017, 11:50:51 PM   #22
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Default Re: Leaking Rear Differential That Pops/Grinds/Cracks????

So I'm the case an Allen bolt did back out, which I'm pretty sure at least one did because I just found a chopped up head inside the fill hole without even pulling the cover, what do I do now?
I'm gonna guess the answer is "pull the cover and look at the insides itself".

It's gotten to dark to pull now so I'll investigate and hopefully get the cover off tomorrow.

I'll attach a photo of the Allen bolt I found when I get back to my desktop.

Last edited by thirtysixnick; Fri, Feb-17-2017 at 02:13:39 AM.
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Old Fri, Feb-17-2017, 02:38:01 AM   #23
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Default Re: Leaking Rear Differential That Pops/Grinds/Cracks????

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So I'm the case an Allen bolt did back out, which I'm pretty sure at least one did because I just found a chopped up head inside the fill hole without even pulling the cover, what do I do now?
I'm gonna guess the answer is "pull the cover and look at the insides itself".

It's gotten to dark to pull now so I'll investigate and hopefully get the cover off tomorrow.

I'll attach a photo of the Allen bolt I found when I get back to my desktop.
Start hunting for a new diff.

-tapa
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Old Fri, Feb-17-2017, 03:51:04 AM   #24
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Default Re: Leaking Rear Differential That Pops/Grinds/Cracks????

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Start hunting for a new diff.

-tapa
Not jumping to conclusions but; For the new differential, what exactly should I look for???
I see a bunch of just rings and pinion gears together and they don't look expensive.
Do I need the whole casing and such or???
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Old Fri, Feb-17-2017, 02:57:17 PM   #25
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Default Re: Leaking Rear Differential That Pops/Grinds/Cracks????

just buy a used diff from someone. 3.23 LSD is the stock ratio for your car but you can go a little higher if you want better acceleration. keep in mind the higher you go the higher your rpm will sit on the freeway, so its a tradeoff.
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Old Fri, Feb-17-2017, 05:02:46 PM   #26
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Default Re: Leaking Rear Differential That Pops/Grinds/Cracks????

Yeah, just find a used diff, preferably local to you. 3.23 is the stock ratio. Automatic M3s had a 3.38, which is a nice "upgrade". Make sure it's an LSD, whatever you buy.

There's some helpful info here that describes removal, how to check the ratio, and how to check to make sure the diff is a LSD:
http://www.m3forum.net/m3forum/showthread.php?t=357718
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Old Tue, Feb-21-2017, 04:48:25 AM   #27
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Default Re: Leaking Rear Differential That Pops/Grinds/Cracks????

So me and my father pulled the cover earlier today and honestly the differential appears to be okay???

We couldn't find anymore of the chopped Allen bolt than we did soooo...??

Do we need to replace said Allen bolt that was backed out, is it unfixable, or is it possible to just assemble it all back together with a new gasket and run okay??

Sorry for noob'n and thanks again for the replies
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Old Tue, Feb-21-2017, 08:30:11 PM   #28
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Default Re: Leaking Rear Differential That Pops/Grinds/Cracks????

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So me and my father pulled the cover earlier today and honestly the differential appears to be okay???

We couldn't find anymore of the chopped Allen bolt than we did soooo...??

Do we need to replace said Allen bolt that was backed out, is it unfixable, or is it possible to just assemble it all back together with a new gasket and run okay??

Sorry for noob'n and thanks again for the replies
Yes, you need to replace any missing fasteners. If there was only one that backed out, and you don't see any damage, you can definitely try running it. But with your description of the noises you were hearing, I wouldn't get your hopes up. You can't see *everything* in there by just looking into the casing, so it's possible that there is damage hiding. Based on your description, I'm surprised you didn't find any gear damage.

Did you spin the gears to check all the teeth for visible damage?

Did the backed out bolt get sheared off, or did it back out completely (do you have to deal with a sheared off bolt)?
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Old Tue, Feb-21-2017, 09:34:38 PM   #29
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Default Re: Leaking Rear Differential That Pops/Grinds/Cracks????

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Originally Posted by fiveightandten View Post
Yes, you need to replace any missing fasteners. If there was only one that backed out, and you don't see any damage, you can definitely try running it. But with your description of the noises you were hearing, I wouldn't get your hopes up. You can't see *everything* in there by just looking into the casing, so it's possible that there is damage hiding. Based on your description, I'm surprised you didn't find any gear damage.

Did you spin the gears to check all the teeth for visible damage?

Did the backed out bolt get sheared off, or did it back out completely (do you have to deal with a sheared off bolt)?
I can't physically see any damage to be honest. I spun both wheels both ways while in the air and it really didn't seem to make the same plastic gnashing noise. I'm not getting my hopes up by any means though. Is there any sort of photo you could post or link you could give me to point me towards where the allen bolts are? I'm going to guess the only thing that backed out was just the head of the allen and that the rest of the allen is still popped in wherever it needs to be...

Thanks for the reply.
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Old Tue, Feb-21-2017, 11:57:55 PM   #30
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Default Re: Leaking Rear Differential That Pops/Grinds/Cracks????

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Originally Posted by thirtysixnick View Post
I can't physically see any damage to be honest. I spun both wheels both ways while in the air and it really didn't seem to make the same plastic gnashing noise. I'm not getting my hopes up by any means though. Is there any sort of photo you could post or link you could give me to point me towards where the allen bolts are? I'm going to guess the only thing that backed out was just the head of the allen and that the rest of the allen is still popped in wherever it needs to be...

Thanks for the reply.
I'm pretty sure one of mine backed out but the noise went away after a couple miles and then the rest backed out about 20,000 miles later

-tapa
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Discussing Leaking Rear Differential That Pops/Grinds/Cracks???? in the E36 M3 (1992-1999) Forum - {Euro - S50 B32 321hp @ 7400 rpm} {U.S. - S52 B32 240 hp @ 6000 rpm}
Total Produced: 71,212 - Years Produced: 1992 to 1999 at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)