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Thread: Dumb Question - Diff Bolt Installation Order

  1. #1
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    Dumb Question - Diff Bolt Installation Order

    So it's been a while since I swapped my diff. This time I'm doing an adjustable camber arm install solo. Everything was (surprisingly) smooth until I had to bolt the diff back into the subframe. I can't seem to figure out the optimal order to put the three bolts back in. If I put the two rear diff bolts in first then there's no way to get the hole lined up for the front diff bolt (front of diff is too high). I tried putting the front diff bolt in first and it started cross threading at some point, probably because it wasn't at a great angle to start out due to the rear of the diff floating around. Just getting the front bolt started seemed like an achievement while shoving the diff around and working the jack under it with my legs to adjust the height.

    Anyways, taking a break to eat. If anyone's done this more recently than me, please share your secrets. My rear end is on jackstands, so "use a lift" isn't really gonna happen.
    1999 M3/2/5 - Titanium Silver - Track/Weekend Toy


  2. #2
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    rear bolts first in loosely. Use a pry bar to lift the diff housing to align the front holes.

  3. #3
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    yea like scooper said. I use a jack under the diff to help with alignment.

  4. #4
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    Pry bar to lift the front and a big screwdriver to insert in diff and bushing to line them up to one another.

  5. #5
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    Thanks, I'll go finish it this afternoon. I'll loosen the ears a bit and will see if I can help line up the front bolt with a screwdriver or something.
    1999 M3/2/5 - Titanium Silver - Track/Weekend Toy


  6. #6
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    Yes, that's also what I did.

    1) Get back two bolts in loosely. Leave maybe 1/2" of play.
    2) Put a floor-jack under the diff, apply a little lift/pressure to get the front part up some.
    3) Put a screwdriver in the front hold. Add and remove height from the floor jack (by raising and lowering it little bits at a time) while wiggling the screwdriver around until you feel everything line up.
    4) Start the front bolt. Get it snug.
    5) Torque rear bolts to spec. Then front to spec. Then double check torque specs of front then rear one last time.

    Before you do all this, it's also worth doubling checking that all the threads on the bolts and bolt holes are still good. Screw the bolts in without the diff installed to make sure everything runs down properly. My front diff bolt inner threads had completely melted, which caused issues. So I had to do the M14 bolt upgrade. Regardless, definitely use a new front diff bolt.
    Last edited by wintershade; 05-24-2017 at 10:11 AM.

  7. #7
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    I replaced my front bolt a few years back when I swapped diffs, so it's still in good shape and looks basically new. I chased the threads to clean up some junk from when it cross threaded a bit, and it looks fine.

    On another note, there's these weird "nuts" that sit up in the subframe which the camber arms bolt into. These:

    https://www.ecstuning.com/b-genuine-...e/33326760364/

    One dropped out when I removed the original arms and it took me a few minutes to figure out what it was or where it went. I came to the realization after I tried to bolt the arm on that side in and the bolt just kept spinning and not getting snug. I still need to somehow hold it in the narrow slit in the subframe and thread the bolt through it, which could be interesting. At least the other one stayed put.
    1999 M3/2/5 - Titanium Silver - Track/Weekend Toy


  8. #8
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    Needle nose pliers or vice grips. You don't need to hold it to tighten it. Only to start it. Once you start it the nut will turn pushing the protruding portion against the subframe to let you torque it down.

    By the way, you're going to want to torque your arms under load. I dropped my car down onto it's wheels on ramps so I could still fit under there and torque it while in it's resting position. Otherwise you'll get preload that will wear out the bushings faster.

  9. #9
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    Yep, already planning on either crawling under the car while it's on the ground to tighten the bushing ends enough so they won't move (and then put in the air to torque), or setting it on ramps like you did. The TMS arms came with pretty detailed instructions.
    1999 M3/2/5 - Titanium Silver - Track/Weekend Toy


  10. #10
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    btw 70 ft lbs for m12 bolt. 110 for m14 bolt.

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