Differential Rebuild

#1

Is it possible to take an open 3.73 dif and convert it to a LSD? And if so, what parts do you need and where can you get them.

#2

To be legal in this series you would need a BMW diff with an LSD with a ratio that you don’t need.

diff-ratios.jpg656x632 103 KB

Easier to find a 3.73 with the diff.

#3

The open diff is a 3.73 from a 89 BMW 325i. Just curious if it’s possible to convert that dif to a factory spec LSD. Is it only a matter of getting the LSD clutches, shims, etc or not even possible.

I get it wouldn’t be easier just to find a 3.73 LSD but is it cheaper. I have an extra 3.73 open diff. Is another option to find a broken lsd (maybe with a bad housing) and swap the inards?

#4

It’s not that easy. You basically need to do the same as this.

IMG_2724
IMG_2724.JPG3264x2448 1.47 MB

This is for a 240sx. I converted my open-> right to a torsion on the left. You still need the diff to convert it; see the big casing.

Note that the torsion is around 500$ for that model.
E30’s you can get a healthy diff for around 350.

Found this while doing so BMW research.: Differential LSD swap
Hope this helps.

#5

I once had a shop swipe my LSD diff and sub in a open diff. Took me months to figure out what the hell was going on. I figured that my diff clutches had given out so I bought a rebuild kit.

Then I pulled my diff and put it on the workbench. I pulled out the “how to replace the LSD clutches guide” (by Chuck Taylor) and was totally confused by how different my diff looked then his pics.

And I’d not opened the diff yet.

The differences in the diff aren’t only inside. The output flanges are totally different. Just score a used LSD diff.

#6

How difficult is it to put 3.73 gearing into a 2.79 lsd?

#7

Sounds like a good plan. If they are both medium casing it’s just about moving the lsd and shimming bearings back to stock spec.

You would take the LSD out of the 2.79 and put the LSD into the 3.73 pumpkin/casing. (half shaft and all)

The reasoning is that the pinion gear is the worst part to shim, not moving it saves a lot of time.

#8

SBKramer, I don’t think the 2.79 will work. I believe the flange on the LSD for that ratio is thicker due to the pinion diameter needed for that ratio. IIRC the 2.79 and 2.93 have their own LSD unit.