How to mate a M3 automatic diff to 6-bolt driveshaft?

[eurospec#19]

I'm close to buying a 3.38 LSD from a 99 M3 automatic. Unfortunately, it has a 4-bolt input flange and my driveshaft has a 6-bolt output, what's the best way to mate the two? I would rather have a 6-bolt input to the diff, so would that mean the whole diff needs to be torn apart to swap the input shaft or can the input flange, itself, be swapped without tearing apart the diff?

[DSK M3/4]

i would take the d/s to a d/s specialty shop and have them modify it to fit the diff. you may be able to modify the diff; not sure.
there is a place in socal called driveline specialities, iirc. i believe they are in cypress. they've done some pretty solid work in the past; they may be able to help you out.

[Rob Levinson]

You could simply swap flanges.

A 30mm nut holds the flange to the diff, you remove the nut from your original diff and the new diff, and complete the swap.

There are some important details, specifically considering the pre-load:

Mark the nut relative to threaded pinion shaft, undo the nut, put the new flange in placee, replace nut until you are about 1/4 turn from mark. As you tighten slowly, turn the shaft to feel for tightness. If you get any, back off.

...and those little details are why I usually recommend a trained professional handle such things.

- Rob Levinson

[eurospec#19]

So a flange is possible!! Thank goodness! Rob, I'll take your advice and get a professional to swap the flanges. Thanks for the help.

[MCubed]

Rob is correct. Have a professional swap the flanges. I just had this done two months ago at Curry's as it has to be done correctly. If you overtighten the nut, you run the risk of damaging the seal around the input shaft. If this occurs, then you have to tear down the diff and rebuild it.

By the way, it is a great upgrade and well worth the effort.