Small Case VS Large Case LSD Identification

[Flatsix]

Other than case size, how does one distinguish between a small case LSD versus a large case LSD.  Can one tell via serial number or number of bolts which hold the aluminum rear case/cover on?

I currently have a 91 318is with a 4:10 non LSD final drive and am looking to purchase a small-case 4:10 LSD but want to make sure the LSD I purchase is indeed a small case LSD.

Also, is an LSD case for model year 1991 318is larger than a non LSD case for that same particluar year due to clutch pack?

Flatsix
1991 318is

[jetteman]

small case lsd versus small case non-lsd are the same size. as for the different diffs i assume you mean a small case versus a medium case diff (given that these are the only two that fit in e30's). i would go with the medium case because it will withstand any mods you do to the car no problem. the differences between the two are the fact the the medium case is slightly longer and has 8 bolts holding the cover on and the small case has 6 bolts holding the cover on. oh and by the way the 4.10 med case only came out of e30 6cyl. auto. and m3's.

[Flatsix]

Given the increased length of the medium case diff then wouldn't I need to replace the driveline with an early 6cyl, auto M3 driveline.  Also, isn't there a weight penalty if going with medium case diff.  I have one of each and the medium case diff is easily 25-35lbs heavier. thanks

1991 318is

[e9nine]

Given the increased length of the medium case diff then wouldn't I need to replace the driveline with an early 6cyl, auto M3 driveline.  Also, isn't there a weight penalty if going with medium case diff.  I have one of each and the medium case diff is easily 25-35lbs heavier. thanks

1991 318is

No need to replace your driveshaft, don't forget the driveshaft's threaded spline section allows a few mm of movement to lengthen and shorten as needed.