mlytle
mlytle

How to Replace a Differential

Had not seen full “how to” for diff swap, so here you go.

Simple job. Well, simple on a car that gets its diff swapped a lot. No promises on a diff that has been in a car for 40 years…

What you need:

A diff

Two 17mm combo wrenches

17mm socket

19mm combo wrench

19mm socket

17mm socket

6mm hex socket (for 2002 cv joints)

8mm hex socket (if you have 320 cv joints)

Jack stands

Jack

First, get the car up on jackstands.

Remove muffler

DSCN5648.jpg

Lock e-brake and put car in gear

Loosen the 4 nuts connecting drive shaft to diff (17mm). you will need to get at them from the right side of diff and will have to rotate the drive shaft and re-lock once.

DSCN5650.jpg

Loosen the 24 hex bolts that hold the half shafts to the diff and wheel hubs. 6mm hex for 2002 cv joints, 8mm hex for 320i joints. You could get away with just doing the inner ones, but gives you more room to work if you just take them all the way out.

Creative use of a combo wrench applied to a short hex key if that is all you have.

DSCN5651.jpg

Or use hex socket and drive

DSCN5649.jpg

Halfshafts out. Good time to check cv joints and refresh if needed.

DSCN5653.jpg

Now get a jack under the subframe to support it. without the diff attached, the subframe will sag. Not good for the mounts.

DSCN5652.jpg

Remove hanger bracket. I just a tranny jack under the diff to support. Or you can have a buddy bench press it.

17mm combo wrenches on the bracket, 17mm socket on the nuts holding diff to bracket.

DSCN5649.jpg

remove the 4 bolts holding the diff to the subframe. 19mm combo wrench on top, 19mm socket on bottom. impact gun is wonderfull thing here.

DSCN5654.jpg

Lower back of diff first. When clear of tank, slide out.

DSCN5655.jpg

DSCN5656.jpg

If swapping in a 320 3.91, you will need to use the 2002 diff cover. Good time to check the innards and reseal the cover anyway.

Remove cover with 17mm socket and scrape the old gasket/goo off cover and diff.

DSCN5657.jpg

Bmw specifies a paper gasket on the cover, but I have never used one in the dozens of diff covers I have sealed. Never had a leak. I use permatex ultra black sealant instead.

DSCN5658.jpg

Apply a bead around diff

DSCN5659.jpg

Replace cover gently. Screw bolts in until just snug by hand. You should see just a little ultra black ooze out. Let diff sit for an hour or two for goo to set.

DSCN5660.jpg

Once goo has set, torque cover to 32ftlbs.

Get new crush seals for fill and drain plugs….these are on use items. Do not reuse.

DSCN5661.jpg

Now is the good time to refill the diff with oil. I use redline 75w90 for street diffs. Redlilne lightweight shockproof oil for track diffs.

Assembly is reverse of the above process…..but when I put mine back together I will add detail to this.

the oils..

DSCN5662.jpg

much easier to fill diff like this than when it is in the car. takes 1.1 qts

DSCN5663.jpg

DSCN5664.jpg

fill to here

DSCN5665.jpg

diff plugs get 41ftlbs

installed

DSCN5666.jpg



User Feedback


Thanks for this. 

 

If you are swapping to a 320  (3.91) LSD, the 2002 half shafts do not bolt right up. 

 

I know there are a few options to adapt them but not exactly sure of the detals.  Also the bolt holes are different on the shaft vs 320 diff.

 

It would be great if you could share the "how to" install procedure along with the parts necessary to do the swap.

Share this comment


Link to comment
Share on other sites

Great! What I would like to know is how this gear ratio will affect the performance of the car eg: will the refs drop but runs faster or what?

Share this comment


Link to comment
Share on other sites

Thanks Marshall, this is an excellent writeup. Your car is so clean I would rather be working on it than mine. I'm just getting ready to put a 390 limited slip in a 1602 hot rod. Just as I was ruminating and wondering if I had a spare paper gasket I got to the section on the perm tex gasket sealer. Very cool that this sealer work for you over the years without trouble. Thanks again for sharing your methodical conscientious perspective on fixing 2002's.

Sincerely, Peter

Share this comment


Link to comment
Share on other sites


Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now