bought a 3.91 diff for a 320i

[ssornerrad]

i think i've messed up and bought the wrong one (3.91) . can it be used if the prop shaft is altered or something?

[Andyboy]

No problem. Look on the prop behind the centre bearing and you'll see a big collar nut/sleeve. Loosen this and tap the diff end of the prop in about an inch. Fit the 3.91 diff (everything else is the same), bolt the prop up to the diff and tighten the sleeve collar nut, as you're doing this try to push the two halves apart to put a bit of preload on the centre bearing. I've never bothered and never had any trouble but it's not a bad idea.
You'll need to remove the alloy heat shield to do it.

[ssornerrad]

thanks andyboy

are you the author of the "restoration bible" ? if so congratulations it's a fine book and has turned me into a e30 nerd.