E30 Zone

have just taken my 3.91 open small case diff out of my 316, and had a 535i E28 3.07lsd to fit. i read somewhere on this site that it would fit in, (with correct driveshafts) and that the back cover can be changed, have found that the diff wont fit as theres a cross member in the way, which i would have to cut a bit out, and put another one in. have i got a different 5 series diff?
also have found that the 535 diff is 42kg. this is a bit much as i would be adding weight to my track car. and is made from cast iron i think. are all the E30 lsd this heavy, do bmw do any alloy case diffs. im also after a ratio around 3.2 to match my gearbox. any ideas, can i get my 3.91 rebuild anywhere with a different ratio and slipper unit, thanks?

nope, won't fit.

as i understand all other e28 diffs will fit with the driveshafts and rear cover plate swapped, but the 535i diff is from the 7-series and won't go on even though the front 4 bolt holes line up (i tried this too!)

Very little chance of finding a 168mm CWP LSD for your 316 mate.

You may have the 'extra large' diff', which I don't think will fit your car without hassle.

You want a 3.9 325i LSD diff, which uses a 188mm CWP.

thanks may explain the weight of the diff, the 3.91 wont be any good, reason why is that my car has a jap engine and box in it, and the ratio from the starion is 3.54, but i thought that since my car was stripped out and will have alot more torque, i could run a lower ratio. 3.91 just revved up to quickly and it felt like i wasnt moving. do an E30 or E28 run a ratio of around 3.2?

If you can find an E30 M3 dif they have a ratio of 3.25 and they are all LSD difs

Just fitted a 525e (3.07) diff into a E30. This fits in with a change of back cover and output flanges only. This is the so called medium case diff.
316 would have originally been fitted with a small case diff., and the 535 had a large case diff.