Diff swap- do I need anything else?

[rammstein]

I've been looking around, and I just want to be sure I am getting everything I need so I can pretend that this will go smoothly.

1 replacement diff without cover or output flanges
1 worn out diff with cover and flanges to steal from
1 cover gasket
4 new locking flange nuts (for bolts to driveshaft- getting from dealer)
2 liters diff fluid (going to use Mobil 1 75-140LS fluid)

Tools:
19mm Wrench
19mm Socket with Ratchet
17mm Wrench
8mm Allen Wrench (actually hoping to use allen socket if it will fit)
Pabst
Floor jack for gently lowering and raising diffs into position
Lift for putting car up

When I change the output flanges, do I simply unbolt from the old diff and bolt onto the new diff? Do I need to replace any seals for it? Am I supposed to mess around with the CV boots/grease?

[bimmerteck]

13mm wrench (longer preferred)
Prybar

[blefevre]

Why are you using 75-140 and not 75-90?

There are some u-cups and o-rings for the output shafts. They are cheap if you want to replace them.

You won't mess with the CV boots. when you unbolt them ziptie them to the car so they don't drop to the floor.

It can be tricky to line up the bolts when re-installing. I had a friend help wiggle it in place but don't give up if you are alone. the thing is just so heavy and weird shaped.

[rammstein]

13mm wrench (longer preferred)
Prybar

What is the 13mm wrench for?

I assume the prybar is for getting the output flanges off, which due to lack of photographic coverage on the innerwebs I am somewhat in the dark about. Everyone seems to just say 'pop them off'. In my experience, everything is always stuck.

I also plan to put the car up on the lift tonight and soak the buhjesus out of every bolt with PB blaster for the next 2 days so that on Saturday they might actually come loose.

[blefevre]

Yes, you pry off the output flanges. They are held in with a circlip so the prybar works great.

[rammstein]

Why are you using 75-140 and not 75-90?

There are some u-cups and o-rings for the output shafts. They are cheap if you want to replace them.

75-140 is supposedly a better choice for high temp track usage. My car currently does dual duty as both a daily driver and a track-practice machine. It gets pretty hot for that use, and the 75/140 is better for that.

U-cups and O-rings... I'd love it if I had part numbers for those, but realoem.com only has diagrams for small-case LSDs for whatever reason, so I don't know how I would get those numbers. If I could and the dealer had something in stock, I suppose I'd get these, although someone would then have to tell me where they go.

[rammstein]

Yes, you pry off the output flanges. They are held in with a circlip so the prybar works great.

After this prying is complete, I assume the circlip can be reused?

[blefevre]

http://ww.e30tech.com/forum/showthread.php?t=39599

[rammstein]

That is an awesome link. Thank you!

[bimmerteck]

What is the 13mm wrench for?

the 4 drive shaft nuts are 13mm IIRC. (you'll know fore sure when you pick up your parts since you ordered them ;) )

[rammstein]

Apparently they vary in size but are usually 17mm. If my previous history is any indication, they will be triangle-shaped and require a special tool from mexico or something.

[bimmerteck]

Apparently they vary in size but are usually 17mm. If my previous history is any indication, they will be triangle-shaped and require a special tool from mexico or something.

No they are an M10 so they wouldn't be 17mm and they are not triangle shaped.

There are
4 x 13mm at the input shaft
12 x 8mm hex at the output shafts
1 x 19mm through the cover
4 x 17mm through the subframe
1 x electrical connector for the speed sensor

the 19mm requires either 2 wrenches or a wrench and a ratchet. ;)

[MR 325]

The nuts holding the driveshaft to the diff are most definitely 17mm, always.

[rammstein]

I'm trying to do it right- all bolts are currently bathing in PB Blaster in preparation for their easy removal this evening. Stay tuned for the part where something breaks.

In other news, the new pumpkin LOOKS nice at least- after scrubbing like 3mm of solid oily scum off, its actually painted a nice black. Plus, its out of an old 5 series, and it has a drain plug on the side. Now I will have 2 drain plugs!

EDIT- question- one of my CV boots is torn. Is this something that needs to be addressed right away?

[FredK]

Yes, a torn CV is bad news. If anything gets in there, it will wear it down very quickly.

IMO using a tap to chase the case threads (M12x1.5) would be a good idea. I think it helps to get the surface rust out of the threads and makes for a smoother installation.

The diff is pretty easy to install, it's just that it's a little heavy. I like to just thread all four top bolts in like halfway at maximum, so they all smoothly turn--that way you really eliminate the risk of crossthreading. If you bolt up like 3 bolts and tighten them, that fourth bolt won't go in. That's Murphy's Law in action right there.