Yep - bolted right up. The bigger diff is about 20# heavier, but it should also last a lot longer. The new one is also an LSD unit, so I get a bit more traction.
The difference in fuel mileage is very slight. I'd estimate only 2%. You also give up a bit of first gear grunt, and steep highway grades will force you to downshift more often. Still - IMHO - this makes the car SO much better on the highway. It makes 3rd and 4th MUCH better for passing - the gear spreads widen out a bit and you can hold it in each gear a lot longer.
It's been a long time since I did this, but IIRC I had to bend the rear diff mount a good bit to line it all up. I also had a stuck bolt on the speedo sender and couldn't swap it out (the earlier speedo sensors use a different style plug but are functionally identical - you might also want to grab the wiring pigtail just in case). I ended up splicing the old-style connector into the wiring harness.
There was only one easy way to do this too. I had to drop the diff twice to line it all up right. If you can drop the rear exhaust pipe (I couldn't - bolts too rusted) that will help tremendously. I also ended up pulling off the heat shield to re-adjust the driveshaft length, then had to pre-load the CSB again. It was much more work than I'd anticipated. If I had to do it again, I'd replace the guibo & CSB while I was under there.
From what I remember, carefully line up the diff snout with the driveshaft and lift it into place with a jack. Start the four 17mm main carrier bolts into the top of the diff 4-5 turns, but leave them loose - just enough so the diff doesn't drop... Then get the four nuts onto the driveshaft yoke studs a few turns, but don't tighten them all the way either. Then get the diff 'ear' mounted to the car. Finally, tighten up the yoke, carrier bolts & ear. Finally, reconnect the half-shafts and the speedo plug.
Topic: What's the best diff for e30 318is? (Read 14111 times)