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Thread: 3.15 LSD buying advice

  1. #1
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    3.15 LSD buying advice

    I've seen all the great info on doing the swap but haven't found anything about what's considered high mileage for a used differential. Do these things last forever or is their some gouge on what I should look for while shopping for one?
    Thanks,
    Spike

  2. #2
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    same boat as you...
    no good 'test' that i've found short of tearing it down and checking wear on the bearings and clutches.
    you could always drain the oil and hope for no chunks.

  3. #3
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    Yeah, chunks would be bad

  4. #4
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    I bought mine with unknown mileage and already drained, but it looked clean.

    These diffs are so cheap, I feel like it's worth the risk. Mine was $200 from craigslist...

  5. #5
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    Well, the diffs are cheap indeed if you are able to do the work yourself. I had a slightly bad experience where my 3.15 diff (from diffsonlne put in by the PO) went bad due to worn out bearings (of course about 6 years after the PO put it in). I managed to get a replacement diff for cheap but the Indy messed up the install while swapping the flange and the replacement diff went bad within a few months. So now I am on my second replacement and this time around I took the car to a "renowned" local indy that specializes in BMW's only and it has been so far so good.

    My point being if you are doing the work yourself there isn't that much downside but if you having someone replace it for you will be spending more on labor that the diff itself.

    One more thing - most of the 3.15 diff's I have seen have mileage north of 100K, you would be lucky to find something lower. I don't think a diff with close 100k miles is too bad however I'd have some reservations if it is in the 200k range.
    Last edited by akatoch; 04-09-2012 at 11:46 AM.
    ========
    91 850i 6-speed, 03 Infiniti FX35 - Familymobile and winter beater, 2010 Mercedes C300 4matic - wifemobile

  6. #6
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    Quote Originally Posted by akatoch View Post
    My point being if you are doing the work yourself there isn't that much downside but if you having someone replace it for you will be spending more on labor that the diff itself.
    If you're paying someone else to install it, there should be no chance for mistakes...otherwise, what's the point? A friend and I were able to swap this in during a 5-hour window of time with no prior experience and nothing but forums to guide us. It is not worth taking it in for.

  7. #7
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    Quote Originally Posted by olinjohnston1 View Post
    If you're paying someone else to install it, there should be no chance for mistakes...otherwise, what's the point? A friend and I were able to swap this in during a 5-hour window of time with no prior experience and nothing but forums to guide us. It is not worth taking it in for.
    I agree with your point but it does get very challenging to argue with the mechanic if the part isn't brand new they screwed up the install vs. the part being old/defective in the first place.
    ========
    91 850i 6-speed, 03 Infiniti FX35 - Familymobile and winter beater, 2010 Mercedes C300 4matic - wifemobile

  8. #8
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    1988-1990 E32 750iL's had this diff in them. If you can find a low mileage one, you shouldn't have any problem.
    It is always wise to see what condition the oil is in when you drain it.
    '93 850Ci 251,002 miles
    '91 850i 74,488 miles


    ...the price of cool ain't cheap!

  9. #9
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    Quote Originally Posted by akatoch View Post
    I agree with your point but it does get very challenging to argue with the mechanic if the part isn't brand new they screwed up the install vs. the part being old/defective in the first place.
    Understandable...

    Maybe a shop could help source a donor diff for that they would feel comfortable standing behind. They see old BMWs all day long. As long as you are paying for their services, might as well let them do the footwork.

  10. #10
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    I bought a 3.15 differential from a guy in Los Angeles and he specializes in them for $275 plus shipping. He opens them and does all the inspection to make sure they are in great shape. He then cleans the case and makes them look brand new. He paints the cover and replaces all the gaskets.
    I took it to a BMW specialist shop and he thought it was new. The shop installed the differential and swapped the cover from my old differential. The shop didn't change the gasket cover and it leaked. I took it back to him and he had to do the whole job over again for free so he could replace the gasket. No problems since.

  11. #11
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    Awesome, just picked one up with 146k, should get it by the end of the week. Olin, your awesome tutorial is what pushed me to do this. let's hope i'm up to the challenge - never messed with a diff. before!

  12. #12
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    Quote Originally Posted by spikec View Post
    Awesome, just picked one up with 146k, should get it by the end of the week. Olin, your awesome tutorial is what pushed me to do this. let's hope i'm up to the challenge - never messed with a diff. before!
    The hardest thing is swapping the input flange and dealing with the weight of it...You will get an idea of the condition of the seals when it's apart.

    My advice for others would be to try and buy one that has not been cleaned, so you can see possible leaks.

  13. #13
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    Olin, you mentioned in your tutorial about a special plug tool, which you didn't have and said you filled it to spec through the speedo sensor hole - spec being 2 qts. of fluid? I'm guessing this is best done while I have it out - or is it not too hard once it's installed? Is it better to replace the plug or is this "special tool" one of those proprietary BMW things that cost an arm and a leg? Also, noticed you did this about a year ago - any issues or parts you wished you had replaced other than the gasket and bolts? I ordered both, plus a new input seal. thanks again.

  14. #14
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    Quote Originally Posted by spikec View Post
    Olin, you mentioned in your tutorial about a special plug tool, which you didn't have and said you filled it to spec through the speedo sensor hole - spec being 2 qts. of fluid? I'm guessing this is best done while I have it out - or is it not too hard once it's installed? Is it better to replace the plug or is this "special tool" one of those proprietary BMW things that cost an arm and a leg? Also, noticed you did this about a year ago - any issues or parts you wished you had replaced other than the gasket and bolts? I ordered both, plus a new input seal. thanks again.
    It's a simple hex (forgot the size)

    I have it, but since I was doing the job at a friend's house, I did not have it with me. You can find it cheaply at any auto parts store.

  15. #15
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    where are you guys finding these differentials so 'cheap'?
    i've been trawling forums and craigslist to no avail.

  16. #16
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    Quote Originally Posted by BlackBox Tuning View Post
    where are you guys finding these differentials so 'cheap'?
    i've been trawling forums and craigslist to no avail.
    Slightly higher than what I have seen listed before but here is one that looks nice and clean:
    http://www.ebay.com/itm/BMW-750il-E3...#ht_500wt_1156

    You can always call the guy and see if he is willing to work with you on the price.

    Unfortunately most of these pop up on the west coast.....go figure .
    ========
    91 850i 6-speed, 03 Infiniti FX35 - Familymobile and winter beater, 2010 Mercedes C300 4matic - wifemobile

  17. #17
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    yeah, i saw that in the searches earlier...really after the 3.64 final tho.
    got a lead on an open 3.64 carrier and seller is offering a m5 diff to make it lsd but that means full rebuild, ugh.

  18. #18
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    Quote Originally Posted by BlackBox Tuning View Post
    yeah, i saw that in the searches earlier...really after the 3.64 final tho.
    got a lead on an open 3.64 carrier and seller is offering a m5 diff to make it lsd but that means full rebuild, ugh.
    Yeah full rebuilds ain't cheap, you are looking anywhere around 1K.
    Last edited by akatoch; 04-09-2012 at 09:31 PM.
    ========
    91 850i 6-speed, 03 Infiniti FX35 - Familymobile and winter beater, 2010 Mercedes C300 4matic - wifemobile

  19. #19
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    totally capable of doing it myself...tools at my disposal, its more like i really dont want to.
    more work than it should be.

  20. #20
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    I have one stupid question about LSD... Whats the benefit to have on? I know what it is and what it does, but still dont get it. I mean... My former car was '96 SVT Cobra Mustang and there LSD was very nice to have. Dropping the clutch and fooling around and I took it on track several times per summer. But nature of this 8 series is whole diffirent... For example eaven Wokke chipped 850i with auto trany barely if not have power to fry rear tires against brake. Well... Winter & snow would be the only normal sircumstances where you realy need LSD. And maybe if you like to push hard on track or autoX.

    Well... Maybe its just me because I don't have LSD. But I would deffinetly take / buy one.

  21. #21
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    Quote Originally Posted by spikec View Post
    I've seen all the great info on doing the swap but haven't found anything about what's considered high mileage for a used differential. Do these things last forever or is their some gouge on what I should look for while shopping for one?
    Thanks,
    Spike
    It's harder to find one that has failed than it is to find a good one, Nearly all non leaking 210 diffs really last quite a while.

  22. #22
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    Well, I'm half way through this project. Ran into one snag with removing the exhaust - I didn't have magnaflows but at least I had the "screw in"/welded version of the exhaust which meant I had to drop the whole thing from the front bolts. The next surprise came when we unboxed the 'new' differential and found the guy left off the output flanges on both sides. After an hour or so of looking at the multitudes of bolts around the darn thing it and trying to figure out what to do (and having some fine homebrew), we discovered the old ones can easily be popped out through a retaining ring on the inside of the e31 case and easily swapped into the e32 diff.

    When we pulled the differential from the drive shaft, the rubber gasket that Olin says to "be careful not to damage" of course got damaged. Fortunately the local dealer has one in stock (p/n 26111229504) so I'll pick it up in the am. Might be a good idea to pre-order one of these if you're contemplating this mod, it's only a couple of bucks. Overall, not a bad day for a couple of pilot mechanics :-)

    Olin's directions are A-1 and if you're on the fence about doing this, trust me, you can. Just hope the re-mount goes a little smoother Anyway, by tomorrow afternoon I should have a whole new feel to the 840.

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