M50 swap - differential

[mopsdrops]

Hello, i have a 1984 e30 320i with a m50b25. My car originally has a small case diff. I'm planning to use a big case diff from an e30. Is this a straight fit? Or do I need to change something to make this fit? Are the driveshafts the same from a small and big case? Do they both fit? Thanks

[Brianmoooore]

The two sizes are directly interchangeable, with just a slight adjustment to the length of the rear section of the prop, by loosening the sleeve nut behind the centre bearing.
Note that E30 diff. ratios are only suitable for use with an E30 gearbox. If you are using the box that belongs on the M52, you will need a much lower (numerically) ratio.

[B7]

He states it's an m50 Brian not m52.

[mopsdrops]

Ok thanks guys. So the diff will fit into the mountings and stuff without modifications. Okay clear. Thanks.

What about the two driveshafts? Are they different the ones from a small vs big case? Or do they both fit?

[jmc330i]

The driveshafts are the same, it's the output flanges that differ between the two sizes of diff - it will be obvious when you have the two diffs side by side.

As Brian said, other than possibly needing to adjust the prop length, the diffs are directly interchangeable.