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Thread: M3 Limited Slip Repair

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    Question M3 Limited Slip Repair

    Hey y'all,

    I'm about to begin repairing a '95 M3 3.15 LSD diff I bought used. As a refresher, upon pulling the drain plug, I stuck my finger into the differential and felt something loose. I removed the rear cover and these are what I found.....

    Four mangled bolts in the bottom of the housing:

    Admin's Comment - 3/31/04
    The writeup is located here... http://www.bmwhow2.com/techarticles/.../lsrepair.html

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    Here are the four bolts that came out along with one good one I removed. Like many of the remaining bolts, it was only finger tight:

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    As you can see, space is tight for the allen wrench, so I had to cut one down in order to get access to the bolts that are still there. Here you can see a hole right above the allen wrench where one of the other bolts backed out:

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    So my questions now are......

    1. What is the torque spec for these bolts? More than likely I'll just crank on them with some Loctite Red.

    2. Where can I purchase these bolts? BMW doesn't sell them. I plan on taking the good one to a bolt store this week to get it matched up, but unsure if that'll pan out.

    3. To satisfy my own curiosity, what purpose to these bolts serve?

    Regarding the condition of the differential, I think it's salvageable without disassembly. The only marks are three very small chips on the ring gear teeth that fortunately did not leave any cracks for further propogation. A local specialist said they've seen M3 differentials do this many times, particularly in '95 models. They recommended to clean it out, replace the missing bolts, and slap it in the car.

    I'd have taken pics of the chips, but my camera couldn't focus that tightly.

    If anyone has suggestions, let's hear 'em.

    Thanks,
    Tommy

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    Hope you didn't pay a lot for that diff...

    The bolt is part number is 33 14 1 206 924. The dealer can't get this number from the ETK, but the part is available when you give that number to them.

    I can guarantee the chips on teeth will make noise, probably enough to annoy you into taking it out. The gears cannot be fixed.

    So what did you pay for it?

    - Rob

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    Tom,

    Rob is correct the diff could get noisey and without removing the slip assembly you cannot see how bad the pinion gear has been damaged. You need to take the axle flanges out, pull the side covers out , and remove the slip unit so you can remove all the allen bolts.Check the threads ,clean and locktight new ones in, be patient and dont over tighten, they are fine thread.also the metal bits could and probably will damage the bearings.
    -tom b.

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    Thanks, guys. These are precisely my concerns. FWIW, I've had chips almost as bad in the ring & pinions of some solid axle cars I've had with no noise issues. But, that doesn't mean this one won't make noise, that's for sure. It's certainly a bummer, but I'm hoping this thing can be salvaged.

    And bearing wear is also a concern. I plan on cleaning the entire housing as best I can with brake cleaner, but I realize that's not a perfect method. Unfortunately, it's the most feasible as a disassembly/reassembly just isn't cost effective.

    I paid $300 (including shipping) for the diff under the premise that it was a normal, functioning diff. A good price, but not if it's not going to work properly. The seller (bf member GQ_Style) has been in touch with me and I believe he did not intend to screw me. He said he's going to cut me a check to help with the repair costs. (edit: he did send me a check) He also said it was only a few days before pulling it out that his speedometer started acting funny, i.e. that's when these bolts backed out and took out the sensor. So it apparently doesn't have many miles on it in this shape.

    I guess if necessary, I could always look into swapping the LSD unit into my open 3.15 rear end, but I'm not so sure what's involved with that. I've done it on stick axle cars, but from what I hear, it's worse on these units. Anyone know why?

    The chips, BTW, are small. I'd estimate about 2mm X 0.5-1.0mm. There are three of them and they are all on the outer edges of the ring gear teeth.

    Rob, thanks for the part number. How did you determine that?

    Tom, with my shortened allen wrench, I can access all of the allen bolts for removal. Torqueing them to the desired spec (whatever that may be) will be a little more challenging.

    Thanks,
    Tommy
    Last edited by Tommy R; 01-21-2004 at 05:02 PM.

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    Tommy - you have the worst luck with internet purchases! :P

    I'd go find some 12.9 grade socket head cap screws [replace them ALL and torque them in a star pattern], clean the hell outta everything with brake cleaner and compressed air, put the new bolts in with Red Locktite 262 and then a new speedo sensor/gear. Then throw it in the car and see how it works.

    If the guy can give you a partial refund then you’re better off just seeing if it'll work instead of trying to disassemble and rebuild the whole thing. It'll cost more than its worth to rebuild it right - this is a BMW part, after all.

    If its noisy when you put it in then just head back to eBay and try to find another one. Ask for a guarantee on the next one - any loose bolts in the case is a cause for a full refund.

    Is there an aftermarket diff available? Quaffe [sp?] or the like? $$$?
    Terry Fair @ Vorshlag Motorsports

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    Tommy... with the chips being on the outer edge, simply check the pinion pattern (you know, with paint or grease) and see how far out the wear pattern goes. If it's not near the chips, then it will probably be quiet.

    Not sure what those bolts do. Looking at the pictures of an exploded diff, I see no use for that plate :

    If the wear pattern looks good, then I'd pull the diff, clean everything out (air and BP cleaner) install the new bolts and be done with it.
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    Originally posted by Fair
    Tommy - you have the worst luck with internet purchases! :P
    Well, the other purchase fiasco was a local sale. Crappy luck, nonetheless. Ruling on that one soon enough....


    I'd go find some 12.9 grade socket head cap screws [replace them ALL and torque them in a star pattern], clean the hell outta everything with brake cleaner and compressed air, put the new bolts in with Red Locktite 262 and then a new speedo sensor/gear. Then throw it in the car and see how it works.
    That's the plan for now. I also plan on replacing the gear lube soon after installation in hopes to flush out any remaining nasties.


    If the guy can give you a partial refund then you’re better off just seeing if it'll work instead of trying to disassemble and rebuild the whole thing. It'll cost more than its worth to rebuild it right - this is a BMW part, after all.
    Yeah, a rebuild (unless I were to do it myself) just isn't feasible.


    If its noisy when you put it in then just head back to eBay and try to find another one. Ask for a guarantee on the next one - any loose bolts in the case is a cause for a full refund.
    I agree. But, before flying off the handle, I wanted to inspect the damage. I did get a good deal on it so if I need to so some labor and replace some parts, that's okay. If I end up with a gear whine or chewed up bearings, I'll be upset. But, I think (and hope) the seller (a long time BimmerForums member) would stand by the sale and do the right thing.

    Is there an aftermarket diff available? Quaffe [sp?] or the like? $$$?
    Yup, but I ain't plunkin' down that kind of coin!

    Tommy

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    Originally posted by John in Houston
    Tommy... with the chips being on the outer edge, simply check the pinion pattern (you know, with paint or grease) and see how far out the wear pattern goes. If it's not near the chips, then it will probably be quiet.

    Not sure what those bolts do. Looking at the pictures of an exploded diff, I see no use for that plate :

    If the wear pattern looks good, then I'd pull the diff, clean everything out (air and BP cleaner) install the new bolts and be done with it.
    Thanks, John. I have some gear marking compound so I'll do that soon. Good idea!

    Tommy

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    Hey Tommy, I've got like 5 quarts of Amsoil 75W-90 sitting around if you want some. It was earmarked for my Subaru, but since I don't have that anymore, I don't need quite that much fluid.

    Keep posting on how this thing works out for ya. I'm curious about how this diff work goes for you since I am going to need an LSD myself sometime soon, assuming my checking account can survive it.

    -Bret

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    Hey Bret!

    I see you picked up a Bimmer. Got any details?

    I'll definitely let you know how the work goes and may be interested in that Amsoil, too.

    Tommy

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    Originally posted by Tommy R
    Rob, thanks for the part number. How did you determine that?
    I have a "special" version of the ETK. It was not easy to get, you have to trade something rather pricey to get it. You can see how full-featured it is: click here.

    - Rob

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    Originally posted by Rob Levinson
    I have a "special" version of the ETK. It was not easy to get, you have to trade something rather pricey to get it. You can see how full-featured it is: click here.

    - Rob
    Cute. My ETK must be the kind where I get to keep my soul...

    Tommy

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    Checked the wear pattern tonight with some gear marking compound and it looks fine to me. Yes, the pattern runs over the chips (at least somewhat), but I'm willing to try it out. Like I said, I've seen worse not make noise so it's worth a shot in my book.

    I also sprayed a ton of brake cleaner in there and cleared everything out as best I can. I'll pick up some replacement bolts tomorrow (anyone know where I can get a torque spec??). Rob, would that be in your magic ETK?

    While at the dealer, I'll also pick up one drive axle bolt. You know, the torx headed ones. I'll get it matched up at the bolt store to an equivalent hex-headed one so there will be less chance of stripping it. I plan on replacing all of them, obviously. I'll do a write-up of the swap while I'm in there.

    I guess that's about it for now. Hopefully reassembly can begin in just a day or two!

    Tommy

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    Tommy, you are very unlikely to fine the external torx bolts anywhere. Your best bet is to get them from Pacific BMW, or one of the other BMW dealers that do mailorder. My local dealer wanted $5 each for the axle flange bolts. I got them from Pacific BMW for $0.66 each! While you are at it, I would also recommend new "locking plates", or whatever they are called. The bottom of the torx bolt is serrated, and bites into these plates. Not absolutely necessary, but would be nice to replace.

    Good luck!
    Butch (who is searching for the DEMON ETK...ebay perhaps? )

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    Thanks, Butch. Actually, the local dealer had them for like a dollar each or so and they were in stock! I just happened to inadvertently throw it out when I was cleaning up this past weekend. D'oh!! :

    Ah well. I'll try them tomorrow, but if no luck I may very well give Pacific a call. Thanks for the info!

    Tommy

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    Tom

    Its not as hard as you think to pull the diff apart as I suggested to better clean the bolt holes and get the proper torque sequence on the bolts. If you are not comfortable with it I understand.You do need to use some sort of star or criss cross pattern when you tighten them if you were to completely dissassemble or just replace the missing bolts and go from one side to the other until you have them all replaced.As far as torque specs just tighten the bolts as best you can without stripping the heads use the red lock tight.The job of those bolts is to hold the top cover in place, beneath it is the clutch packs,shims,spiders gears basically the guts of the limited slip.There should be 8 bolts maybe 10.Torque is not that high because they all work to keep unit assembled..the lock tight really does the job. Dont know why this seems common on E36 M3 as other BMW diffs are nearly identical and I have never had a problem in the diffs I have worked on and rebuilt.....email me if you have any problems let me know how it turns out.
    GOOD LUCK...tom b

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    Originally posted by tombmwe30
    ...If you are not comfortable with it I understand...
    I don't beleive Tommy is uncomfortable with doing this. He (along with a couple others of us in this thread) have rebuilt many a ford differential (and some chebbies).... and its really no big deal.... but the specs for those are all readily available.

    I'm guessing the biggest level of discomfort comes from the fact that for $300 he got a POS BMW differential whereas for $50 he could have got a Ford unit in the junkyard that would have been A-OK.

    Tommyboy.... couldn't find the torque specs anywhere. I bet if you ask at the parts counter one of the techs could look it up for you. I know I would if you asked me :

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    Thanks, guys...

    Tom, I'm just wondering what's involved in removing the LSD unit and then re-installing it properly. FWIW, I can access all of the allen bolts, so no issue there. I was just planning on re-inserting some new ones (star pattern, loctite red). Is this a straight-forward procedure? Like John said, information on rebuilding a BMW diff is not readily availble, like it is on the pony cars we're coming from....

    John, good idea on the parts counter guy. I'll ask him when I go. It'll be either today or tomorrow...

    Tommy

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    Originally posted by John in Houston
    I'm guessing the biggest level of discomfort comes from the fact that for $300 he got a POS BMW differential whereas for $50 he could have got a Ford unit in the junkyard that would have been A-OK.
    Yea, and a cheap Ford 8.8 diff is also rebuildable [clutch packs] and adjustable [clutch preload spring & tolerances] and upgradable [extra cluth packs]... for like $50 in parts! Well, it helps to have the ford diff stack tool, but you can do it w/o. The Ford 8.8 is also hella strong - stronger than even the biggest BMW ring and pinion, the 8.2" in the E46 M3/M5/7 series, I believe. Bigger ring gear = stronger.

    I was tempted to adaprt/use a Ford 8.8" LSD IRS in my E36 LS1 swap, because I got an entire 8.8" IRS rear assembly for $250, any gearset is ~$150, and there are tons of aftermarket and stock diffs available. And the aluminum carrier IRS diff is finally getting cheap.... the 8.2" iron E46 M3 IRS diff assembly is 110 pounds!

    But... the thought of being able to BOLT IN the E46 diff assembly won out, and Matteucci hooked me up with the entire diff carrier assembly. Just need to find E36 Euro halfshafts and diff mount.... anyone got any leads on Euro E36 M3 parts?

    Wanted To Buy:

    (Edit: have since found out that I need the following parts)

    Euro E36 M3 halfshafts or
    US E36 M3 halfshafts [that I can have shortened]
    Euro E36 M3 rear cover [diff mount]
    US E36 M3 rear hubs/uprights/brakes

    contact: fair@vorshlag.com

    Thanks,
    Last edited by Fair; 01-15-2004 at 10:24 AM.
    Terry Fair @ Vorshlag Motorsports

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    Jeez, and it takes me half an hour just to change my oil! I feel so outgunned here I think I'll have to go unbolt something from my car tonight just to make myself feel better...Not that I'll do anything with the part; Probably just hit it with a hammer for a while and then bolt it back on, but you know, just do something to make myself feel mechanically inclined

    -Bret

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    Tom

    Hope I didnt insult you, I dont know you ,and anything new can be a pain until you have done it once or twice.just take the axle flanges out, they just pop out,may need to use small pry bar because they are held by a large C clip. Then remove the 13mm bolts on the side covers of diff. twist it and pry at same time and it will come out along with spacer. Do one side at a time and keep them separate,label if necess.It is VERY important that you keep the left side cover and spacer on left and right on the right, of course.These covers are machined and fit tight be patient.once you have both out you can roll the whole slip assembly out to better work on it. i understand about the torque specs but TRUST me clean and use the lock tight and you should be fine,if I had to guess I would say around 15 ft lbs .Torq. the side bolts at 22ft lb.After reassembly check to make sure it still spins with same resistance as before diassembly. Tom b

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