Swapping the diff

[crashnburn80]

My manual tranny died, so I am replacing it next weekend. Reverse is totally shot and non-functional, and 3rd gear synchro is worn. Since I'll be dropping the tranny out I figure its a good time to swap the diff. I've pulled the tranny before but never the diff, is there anything I should know ahead of time? Non-reusable parts I'll need ect. I am swapping with a 3.73 LSD, is it a 100% direct bolt in?

[632 Regal]

hmm...

http://www.bimmer.info/~regal632/rearend.html

note the flange swap if needed.

[Robin-535im]

Some advice, take it or leave it... :)

1) Get a stiff wire brush and clean all the crud out of the torx bolts that hold the half shaft to the hub & to the diff output flanges. They get filled in with years of road grime and often they are really tight. When you stick the torx driver in, it compresses the crud to the bottom of the hole and you think you have a good grip on the bolt... but you soon realize how easy it is to strip torx bolts! I reused all my bolts and put on a little locktite blue (medium strength). Cleaning the crud makes reassembly peaceful and pleasant. If you're flexible (and use a u-joint + extension on the socket wrench), you can get all six out per joint without rotating the wheels, hence you can keep the p-brake on and do the job in one sitting.

2) get new output shaft seals, see the recent post... pretty easy to change them and they're only a few bucks.

3) change the big rear carrier-to-car bushing while you're in there, the one right up against the gas tank. Not required, but if you're changing things out anyway it's a good time to do it. It's one of those things on Bill's list-of-things-that-break on E34's.

4) check your half-shafts for play when they're out. Grab one end and twist the other back and forth. Good ones will have no play, mediocre ones will have a slight click & a little tiny bit of play. They're not too pricey, maybe $80 a side? If you're getting a new tranny anyway, might as well get all the slack out of the drive line you can. You'll appreciate the mental satisfaction that the driveline is as tight as a new car.

HTH

- Robin

[Jeff N.]

Robin's on target with his suggestions.

Assuming your 3:73 is from an early 525i manual, here's what to expect.

- Driveline will bolt to the input flange, no swap required.
- You'll need to swap the output flanges from your current. The beauty is that this is a 2 minute job and requires no tools.
- Bolts straight in. Heavy bastard. A jack and a second set of hands can help. No need to pull the exhaust if I recall.

If you do alot of highway driving, you may not like the gearing. Engine spins about 2800k at 70mph in 5th. With this rearend, I find my car likes to cruise more in the 60mph range at the 2200k rpm range. Will give you more around town zip, that's for sure.

Jeff




My manual tranny died, so I am replacing it next weekend. Reverse is totally shot and non-functional, and 3rd gear synchro is worn. Since I'll be dropping the tranny out I figure its a good time to swap the diff. I've pulled the tranny before but never the diff, is there anything I should know ahead of time? Non-reusable parts I'll need ect. I am swapping with a 3.73 LSD, is it a 100% direct bolt in?

[632 Regal]

Even if the input flange happens to have the correct bolt circle the holes may be different sizes...that one blew my mind, same with the side flanges, the ones from my old unit had to literally be beat in, way too tight like the splines were cut differently in comparison to the rear ends requirement. ya do what you gotta do.



Assuming your 3:73 is from an early 525i manual, here's what to expect.

- Driveline will bolt to the input flange, no swap required.
- You'll need to swap the output flanges from your current.
Jeff

[crashnburn80]

I have a tranny jack and a second set of hands to to make the install alittle easier. Thanks for the info thats exactly what I was looking for.