M3 Limited Slip Repair

[Tommy R]

Originally posted by BlueMaxx9
So Tommy, now that you're all experienced in diff refurbishing, how much would it take for you to clean one up for me

-Bret

Heh.... Just beer so long as you drop it out of the car beforehand. Otherwise, we'll have to talk.

Tommy

[BlueMaxx9]

Ahh, the old 'Liquid Remuneration'; Still partial to Fat Tire?

Well, be careful what you say, cause I might just take you up on the offer! It would be kinda cool to try it myself, but I don't think my apartment is outfitted as well as your garage for this kind of work I'll make sure to get in touch if I get a little more serious about this.

-Bret

[Bernman]

Originally posted by Tommy R
Forgot to mention I picked up some bolts to replace the inverted torx bolts that hold the half-shafts to the output flanges of the diff. Unfortunately, it looks like the head of the bolts is going to be too large. I'll see if they have any with smaller bolt heads. Hmmm......maybe that's why they used torx bolts from the factory?

Yeah, a hex cap head bolt will be too large to fit on the axle flange. You could use a socket head bolt in it's place though. Just make sure you use an alloy steel one, and not stainless, or a lower strength one. Only problems with a socket head bolt are that a 10mm socket head uses an 8mm hex key which *might* be a problem to get the proper torque on...but is probably sufficient. The other issue is that the socket head bolt will not have the serrations on the bolting surface which tend the lock to bolt in place. This is probably ok, just an added measure of safety. I considered going this route when my local dealer wanted to charge me $5 each for the bolts, but when I found that Pacific would only charge me $0.66 I went with the BMW bolt

Thanks for all the great pictures and text!

Butch

[Tommy R]

Butch, I'm happy to help and share the info. Good idea on the socket head. I'll see about picking some up tomorrow at the bolt store. No serrations, like you said, but maybe they'll be less likely to strip like these inverted torxs!

Tommy

[Tommy R]

I tried to get some pics of the diff itself, but my camera won't focus that closely for some reason and the lighting and visibility is poor.

Nonetheless, for your viewing pleasure....

[Tommy R]

Another....

[Tommy R]

Can't really see anything from the side....

[BrazeauRacing]

Come on Lil' d! Take it apart for us!!! LOL (just kidding)

[Tommy R]

Originally posted by BrazeauRacing
Come on Lil' d! Take it apart for us!!! LOL (just kidding)

*FWAP!* :

Now way, homeboy.

d

[Tommy R]

Hey guys,

Well, I'm about to start the reassembly this week. I need some torque specs for the allen-head bolts (the ones shown earlier with the white dots on them), as well as for the side cover bolts. FWIW, the internal bolts will get Loctite Red. The external bolts will get blue, I guess.

If anyone can help me find the numbers I need, I'd be eternally grateful.

Thanks,
Tommy

[Tommy R]

Originally posted by John in Houston
Good job Tommy! Any chance of you opening up the diff for some additional pictures???

John,

Check out the blowout pdf at the bottom of this link to see details of the LSD unit.

Tommy

[tombmwe30]

Tommy,
I was just looking at the thread you had going with that guy that was giving you torque specs.The spec I gave was an estimate on the allen head bolts...while it it nice to be specific on things I was taught on these diffs to use lock tite liberally and just get them as tight as you can..obviously without stripping the head which is pretty easy to do. I use IR 3/8 impact on lowest setting with appropriate allen socket.I tighten first till they are all down...meaning the top is flush then I go around one more time in sequence to be sure I have even and enough torq.It is diff to say what finale torq. is since this is going through allen socket which Im sure twists some but Ive never had a problem.Thats why I sad just crank them in w/lock tite and encouraged you to take apart so you could get onto all bolts evenly.I didnt have the internet when I was taught to work on these years ago..so his info is appreciated.maybe as he said when he looked at torq values that some are too low causing this prob in first place...

[Tommy R]

Thanks again, Tom. Yeah, I think I'll do what you're suggesting, i.e. use Loctite Red and snug them up as much as I can, short of stripping anything. Since there was no threadlocker present before, hopefully the presence of it now will prevent this kind of problem in the future!

Tommy

[aweather]

Hey Tommy,

I am almost positive that I am having the same issues with my 95 M3 diff. The symptoms that you described are identical. However I haven't seen the speedo freaking out just yet. I was curious what you would recommend as you have some experience in the matter: I'm not sure if I am up for pulling the diff out of the car so is it possible to take that rear cover off clean everything really well, replace and locktight the bolts, all without taking the diff out? I wouldn't mind so much accept right now the M3 is my "reliable" commuter to work. Thanks for the great pics and tips, very helpful in my situation.

Alex

[Tommy R]

Let the re-assembly begin.......

First, everything was cleaned thoroughly. Here's the driver side bearing race, spacer, and axle flange getting cleaned. I avoided spraying the cleaner on the o-ring. I thought about removing it, but was afraid I'd damage it.

[Tommy R]

Here's all the components. Clean and ready for reassembly....

[Tommy R]

Time to torque the diff down. I used Loctite Red and torqued them as much as I could. First I used the standard 3/8" ratchet shown, then I used a longer torque wrench. Unfortunately, the torque wrench's minimum setting was 5 ft-lbs. or so and that felt like it was on the verge of stripping the bolts, so I simply went as snug as I felt comfortable and left it at that.

[Tommy R]

And the diff goes back into its old home, prior to re-installation of the bearing races, of course....

[Tommy R]

Now the bearing races are in, but I still need to determine the correct torque spec for them. Any words of wisdom here?

[Tommy R]

Originally posted by aweather
Hey Tommy,

I am almost positive that I am having the same issues with my 95 M3 diff. The symptoms that you described are identical. However I haven't seen the speedo freaking out just yet. I was curious what you would recommend as you have some experience in the matter: I'm not sure if I am up for pulling the diff out of the car so is it possible to take that rear cover off clean everything really well, replace and locktight the bolts, all without taking the diff out? I wouldn't mind so much accept right now the M3 is my "reliable" commuter to work. Thanks for the great pics and tips, very helpful in my situation.

Alex

Hi Alex,

Unfortunately, there's no way (that I can see) to take off the rear diff cover while it's still on the car. And if you could, you'd still want to remove it in order to get proper access to the bolts.

Truth be told, I'm very thankful Tom influenced me to remove the diff from the housing. The ring was separating from the differential and there's no way of properly torqueing it inside the housing. And everything I've done here is actually very simple. I even R&R the diff by myself initially. Too bad that's when I discovered this diff was messed up.

If you're hearing noises in the diff and believe you may have the same problem this diff had, you'll really need to remove the diff to replace and re-torque all the bolts.

Tommy

[aweather]

Tommy

Thanks for the advice. F it I will just rip the MF out and give it a whirl. Your pics will come in handy, thanks again. In the mean time I will drive my 8 MPG truck to work. Any special tools needed for taking out the diff? I'm not yet familiar with those inverted torx bolts, where do you get a tool to remove those? BTW a socket cap head bolt would most likely provide the clearance and be a substitute for the wierd bolts. In exteme cases we have machined down the heads of the socket cap bolts for even more clearance but this requires access to a lathe. Just a thought.

Alex

[Tommy R]

Good deal, Alex. Like I said, it's really not rocket science. Just take your time, keep a clean work area, keep left and right sides separate, and if in doubt, take pics to see how things go back together if you catch a snag.

You didn't think I was taking all these pics for y'all, did ya?!? :12:

I don't recall any special tools being needed to drop the diff other than the inverted torx bit. I just picked up a set from Sears prior to the operation. Although, I think a 12mm 12 point wrench could come in handy on the driveshaft bolts. I don't recall my gearwrench working in those tight quarters. :

I think that's about it, but within the week or so I should do a little DIY on R&R the diff housing.

Oh yeah, I'm still debating what I'll do with the inverted torx bolts. Socket cap or just keep them. I'm leaning toward keeping them, actually. I like the idea that they have serrated edges on them, as has already been brought up by Butch, IIRC.

Tommy

[aweather]

I think you can get Socket head bolts with the serrated flange. I'm sure I've seen them before. I'll check with some people at work tomorrow and get back to you.

[Fair]

External Torx headed "E-Torx" sockets are sold by Lisle... I bought my set at Sears. That's after I rounded off three of the bolts trying to use 6 point sockets. Bad idea.

The damn 1.8L in my '93 318 had them all over the place, including the ELEVEN engine-to-trans bolts. "But our's go to eleven." Did I say there were ELEVEN bolts? Of FOUR different sizes!

http://www.vorshlag.com/ls1bmw4.asp

Evil Germans.

[tombmwe30]

Tommy,

Great you are almost done...your side covers should be torqued at about 20 ft lbs, use some med strength lock tite on them too.Check after you torq both sides and make sure it spins freely..if it doesnt back the bolts off and re-torque a couple of pounds less, recheck ..it should be fine. also I always put some syn grease on bearings before I reassemble for protection during this spin test..cant hurt. I see that you have torqued the allens and now prob realize as you said it is difficult to get alot of torque on them w/o unit out and as I said earlier it is the job of the fine threads and locktite to REALLY do the job of holding it together. Good Job...Tom b.