E36 Front Differential Bolt

ASO544 · #1 (**permalink**) 11-21-2015, 08:10 PM

I just did a differential swap in my 2013 BDR. Everything went great but I had one hiccup......the front diif bolt is slightly larger on the stock one than in the one I purchased. Our has a 12.9bolt while the diif I got has the older 10.9 bolt.

The front mount of course has the none threaded area that the bolt shelf sits in and than the threaded area on the diff that it tightens in to. I got a 10.9 installed but there is of course the possibility of some minor play as the 10.9 bolt doesn't fill up the not threaded area like the 12.9 bolt does. I got it tight so no play I can feel but it's gotta be minor movement. Now this bolt location seems to have a breaking issue ( lots on the web about it) as that area has a lot of torque. So not having the proper bolt size seems to be a really weak area especially with out HP levels (427R)

Any idea if I can find a a 10.9 bolt with a 12.9 shelf ( non threaded area) to tightly fill in that front mount area or is it possible to shim the front part of the 10.9 to the size of the 12.9?

The 10.9 bolt pictured below isn't the one I used ( just used it as a measurement) as it's installed in the diff but it's the same design as the 12.9 have a non-threaded shelf and then threads on the end so the measurement may be a hair off compared to the one installed.

Cashburn · #2 (**permalink**) 11-22-2015, 07:08 AM

No, you drill and tap diff for larger bolt. This is a common upgrade in Bimmer Land.

ASO544 · #3 (**permalink**) 11-22-2015, 12:14 PM

Thanks Cashburn.... Knew I couldn't get off that easy!!!!

ASO544 · #4 (**permalink**) 11-23-2015, 06:02 PM

Cashburn,

What size/thread bolt do stock BDRs come with for the front diff mount? Does Backdraft upgrade to a 14mm bolt when they install the diff at the factory?