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How to change a Differential

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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

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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.

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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.

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Or use hex socket and drive

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

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

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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.

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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.

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

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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.

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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.

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Apply a bead around diff

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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.

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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.

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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..

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

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fill to here

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diff plugs get 41ftlbs

installed

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Nice write up, I think I need to pull mine as it's weeping a little, gasket only, no sealant, bummer.

Sounds like you might know a bit about the LSD's. I installed one in my project which seems to groan/pop a little when pushing it around the garage, is this normal or should they be dead quiet? Internally it looked fine, no pitting/scoring/worn gears when i installed it. Car isn't drivable so all i can do is push it about to test, or pull it. Any thoughts would be appreciated.

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hopefully there is oil in that diff you are pushing around.

by design an lsd resists turning. the halfshafts are partially locked together. for the car to turn either the diff clutches have to slip or one of the tires has to slip. the slipping can create a little noise. hard to tell if the noise you are describing is coming from diff, cv joints, drive shaft, spring, etc.

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hopefully there is oil in that diff you are pushing around.

by design an lsd resists turning. the halfshafts are partially locked together. for the car to turn either the diff clutches have to slip or one of the tires has to slip. the slipping can create a little noise. hard to tell if the noise you are describing is coming from diff, cv joints, drive shaft, spring, etc.

Sweet info, kinda the answer i was looking for.

Diff def has oil as I pulled out the half empty bottle of redline xxx fluid last night, not to mention its weeping, there is no oil on the ground, just a film at the bottom of the diff.

I lay on my creeper, head under the car whilst someone pushed it, no tailshaft in place, I'm almost positive it was coming from the diff.

My only other thought was that I hadn't correctly built the half shafts, using wrong cv joints, or omitting the spacers. I'm nearly certain I used 320 inboard and 02 outboard to match the holes/bolts.

Would the half shafts bolt up if I used the wrong thickness spacers?

Not sure of the year of the diff.

Thanks for your time.

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Awesome post. Quick question? Is the crush washer for the diff drain plug the same as the crush washer for the engine oil drain plug. I know I have several engine oil drain plug crush washers but didn't get any for the diff. I was hoping to change the oil in my diff, but don't have any diff-specific crush washers.

 

Thanks ahead of time!

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Awesome stuff....I have a question ,I bought a rear diff these r the numbers inside the rear cover 4061004165...671098. S25 how do l know if it will fit my 76 2002 ....any help would be great thanks ...

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Guy said it came out of a 320 ,I can't tell Ta ratio, the rear cover is different but otherwise it looks the same as the one on this post that u guys are installing,,,

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thanks a lot. I just used this thread to remove my diff.

 

Cleaned it, 28 years of road dirt :s

Gave it a shot of rust paint, since it was out

Re-sealed it and filled it.

 

I'm just waiting to put it back in because I used the paper gasket which I'm a little skeptical about. I figured I'd put it on top of cardboard for a day and see if any oil leaks out. I doubt it will leak now but I fear it will when i put it back in.

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This article is such a big help.  Of note, the pictures in the tech section are broken.  I thought I was going crazy as I could have sworn the pictures were working until I realized it was in two sections.

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I made use of this recently and it was a tremendous help.  few things I noticed when following the guide:

- in the tools needed list, there's no mention of the hex needed for the drain and fill plugs

- would you recommend draining while on the car or after removing the differential

- I has some trouble with the bracket towards the rear of the diff, it seems you removed it when the diff was lowered, did you do the same for putting back on?  put the bracket on diff first, then the car?

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On 10/2/2017 at 9:18 AM, mataku527 said:

- I has some trouble with the bracket towards the rear of the diff, it seems you removed it when the diff was lowered, did you do the same for putting back on?  put the bracket on diff first, then the car?

No. see instruction below.

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