e30 Diff Swap
 

Well, I picked up an e30 325is diff today, although I can't really get started until the engine's done. Here's the first pic:

http://www.318ti.org/gallery/showgallery.php?cat=600

First things I'm seeing here:

1. The output shafts' flanges' holes are indeed further apart than the stock unit. I assume this is where swapping flanges comes in.

2. The input shaft is about 1 cm longer than the 'ti unit as measured to the front mounts. This is not good, I really didn't want to worry about the driveshaft not fitting.

3. The distance across the diff from output shaft to output shaft is about 3 cm longer. This jives with the e30 halfshafts being shorter; I've seen some botched jobs before where the wrong lengths of halfshaft were used and all kinds of problems happened.

I think I'll start by looking at the e30 halfshaft distance and see if that makes up for the difference; that would make this easier. I'm still a little worried about #2 above, however. Hmm...

Andy

I've been waiting for more info on this dilemma for awhile. I have an E30 diff to put in too. Here is my question. What is the flange to flange width of the E30 diff with 318ti flanges, and what is the flange to flange width of the 318ti diff with 318ti flanges?

I plan on putting in the E30 diff with 318ti flanges, and wanna know how much extra width, if any , there will be.

That issue with the drive shaft concerns me. I haven't heard anyone complain about that being an issue.

Eric

notice the ti diff cover extends further back? you'll likely need to "make" a little room in the rear subfloor beam to clear the top of the diff cover, but other than that, it's no problem.

i believe the ti flanges extend out less than the e30 flanges, which is why the swap of flanges and using the ti halfshafts appears to work. that said, i swapped to e30 flanges and halfshafts. i'd be interested to hear if the person was able to swap in the m-coupe halfshafts with no issues. never did hear ...

What is the total benefit of doing this? I'm not too savvy on LSD's and ratio's and all that

higher ration (3.45 -> 3.73) results in quicker acceleration (and a 10% increase in revs turned at the same speed).

typical benefit is getting limited slip as almost all the ti's came with open diffs. the e30 diff can also handle more power (large case diff coming from a e30 325).

so, if my '97 (most likely) has the open diff, I would benefit from getting a LSD for my car which would be an easy bolt on direct replacement and a good mod? Hmmmm... I may have to find one of these "LSD"'s you speak of... :evil_lau:

the only TRUE easy, direct bolt-on, no issues LSD is the 3.45 LSD from the 95 (and i believe early 96) ti's that had it or, it appears, m42/44 z3's that again might have had it. it was even an option for automatics, but that gives a higher ratio, 4.44.

hmmm... thinking... hmmm... I have a 3.73 LSD from an e28 (same as e30 except for rear cover) sitting in my garage, how is drivability with that gear ratio in our cars?

Easy? I have an e30 lsd, while using my ti halfshafts and flanges. Getting the old diff out was a pain in the @$$ because those freaking top bolts are hard to access and were covered in 10 years of dirt. Also, make sure you have that torx socket!!! Sure you can use a hex socket, but you'll probably end up rounding off some of the bolts like I did. Also, since the diff is bigger, I had to pound in some of the metal so it would sit flush.

I'll get some exact measurements in the next few days. I'm going to be racing in the US Touring Car race at Laguna Seca (A1GP Support Race - woo hoo!) on 3/10-12, so I've got a few other details to take care of. I'll try to keep this as updated as possible, though.

The thing about the drive shaft was measured from the front mounts to the end of the driveshaft. It's not that much different, there might be enough slack to just jam it in, but I'm really going to be whomping on this thing, so I don't want it to go bad prematurely. But interesingly, even though the case is differently sized the rear diff plate does seem to be pretty close to the right place.

The width of the output shafts is interesting as well. From the pic, both diffs' output shafts are pretty flush. The interesting thing is comparing the two to my '91 318is - it has a small case diff and huge flanges sticking out several inches. e30s, I think use all the same length shafts, while e36s seem to vary. I may be cruising for Z3's to measure out there, but I'm heading to the junk yard tomorrow morning...

Oh, and I'll start another thread on gear ratios, there are some interesting things about that too. Yes, in general BMWs and particularly those with semi-trailing arms work great with an LSD, whether it be track or autocross, or driving on a slippy road.

When you say the to flanges stick out less than the e30 flanges, are you saying with both flanges in a ti diff? That is what I can't get a straight answer on. I'm only interested in knowing the flange to flange width of an e30 diff with the stock flanges and also the ti flanges.

I understand the E30 diff is not an "easy" install... but what about E36 diffs from the ti's that came with them as Cali-ti pointed out? What would the 4.44 ratio do to my automatic?

no, the ti flanges in the e30 diff stick out less than the e30 flanges in the e30 diff as shown by dredder: http://318ti.org/forum/showthread.php?t=7865

the ti halfshafts are longer than the e30 halfshafts and the e30 diff is wider than the small case diff in the ti. as long as you have no issue with the strength of the ti flanges and halfshafts, i see no reason why it shouldn't work.

if you can find a ti or 1.8/1.9 z3 auto that had a LSD (again, this is a small case diff), it will bolt right in with no issues (and be the same 4.44 ratio as your current automatic open diff). it's going to a large case diff where you run into fitment issues (although not too big of issues).

I think I misspoke. What I want to compare is the width flange to flange of the
stock diff with stock flanges, to an E30 diff with ti flanges. Isn't that the only comparison that matters. I wanna know if the E30 diff with ti flanges is wider than stock setup. If it is, that could be a big problem. From what everyone says, the swap is no problem.