Made my mind up: I'm gonna do a diff swap.. (a few Q's).

[e34.535i.sport]

I looked into doing a diff swap a while ago, and time has went by and I've procrastinated... I've read all the previous threads about diff swaps in the archive but this is kind of a personal thing I find, so thought I'd ask your advice/opinon.

Recently I asked about a diff for a friend in a scrap yard and the dude is willing to do them REALLY cheap if I take it off myself... Which in my eyes is preferrable anyway as I'll learn how to do it and make sure it's done carefully.

So the cost factor is out the way and nothing is holding me back. I should be able to afford it and some new seals when he gets the right one in... [Currently he has a diff from an e36 323i (1998) and an e36 320i (1998 I think)... I don't know if these are suitable or interchangable with mine, I doubt it.] Now, I've done some research and found this page really helpful: http://www.vinesauto.com/diffratio.htm so I know what I'm looking for.

First question is - What ratio would be best to move up to from a 3.46 if I want better acceleration and low end torque? The way I see it my choices are 3.64, 3.73 or 3.91. Any higher and I guess first gear is made redundant? I'm leaning towards the 3.73 but not sure, check this out:

3.64: It's a ~5.2% increase in revs meaning @ 80mph in fifth if I'm normally at 3000revs I'd be at ~3156revs...

3.73: It's a ~7.8% increase in revs meaning @ 80mph in fifth if I'm normally at 3000revs I'd be at ~3234revs...

3.91: It's a ~13% increase in revs meaning @ 80mph in fifth if I'm normally at 3000revs I'd be at ~3390revs...

Looking at that I surely wouldn't lose too much fuel consumption even using the 3.91 diff? Also, I normally shift by 5000revs in any gear meaning even in first if I wanted to get going in a hurry I would be doing the same speed if I just took it a little further to 5650revs...

Next question, which I hope someone can help me with: Which diffs have the same flanges as mine? I really don't want to be changing the driveshaft flange as it's supposed to be a lot of messing. I don't mind changing the output flanges as they're not supposed to be as bad but I'd prefer a straight swap to be honest... I'd really appreciate any info on this.

Ok, also, I have an LSD at present, should I replace it with another LSD? I don't want to lose out on anything by going to an open diff... Oh, and does it matter if the diff comes from a MANUAL or AUTO? I imagine not...


Lastly, what's the deal with this 'preloading - I've read a lot of information on swapping the diff (great resource here: http://www.bmwe34.net/Wiki/tiki-inde...ferential+swap) but still in the dark with the preload. Anyone done it and can I do it?