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new2bmw
11-11-2009, 12:03 AM
wondering what the stock differentials are on a 1984 318i and a 1989 325i?

Eurostyle
11-11-2009, 12:44 AM
4.10 (auto 318) and 3.73 for the 325...

new2bmw
11-11-2009, 12:51 AM
if i swap an m20 into my 318i m10 can i use either diff? if so which one should i use?

Eurostyle
11-11-2009, 01:03 AM
Yes, you can use both...Depends what you want...Do you want to go stock, or have quicker pickup (4.10 will be quicker off the line)

new2bmw
11-11-2009, 01:09 AM
if i am using the 4:10 LSD from my 84 318i you say it will be quicker than whats in the 325i right now. what do i sacrafice for it being quicker off the line? what would you use?

Eurostyle
11-11-2009, 01:18 AM
You would sacrifice top end speed, but unless you need to go 220Kmh every day, its no big deal at all...Sould still be able to go over 200...Highway RPM will be higher, so i gas consumption...like most mods!

new2bmw
11-11-2009, 01:25 AM
hey thanks for the replies. i just looked on this site http://www.e30eta.com/ecdiff.htm and here is what it says.

An important thing to bear in mind about swapping is that six- and four-cylinder E30 BMW differentials are different and will not interchange. The housings and rear axle carriers are totally different. Interchangeability only exists among four-cylinder cars and six-cylinder cars separately. The sole exception is the E30 M3, which uses a six-cylinder-type differential, thus providing a source of 4.10 limited slip diffs for the 325i. In addition, differentials from the E28 5 Series BMWs (1982-88) will also interchange with the E30 six-cylinder 3 Series cars, and this becomes key to modifying the early eta engine E30s.

so i am confused as to whether i can use the 4:10 lsd from my auto 318i with the 325i engine swap.

Eurostyle
11-11-2009, 01:50 AM
hey thanks for the replies. i just looked on this site http://www.e30eta.com/ecdiff.htm and here is what it says.

An important thing to bear in mind about swapping is that six- and four-cylinder E30 BMW differentials are different and will not interchange. The housings and rear axle carriers are totally different. Interchangeability only exists among four-cylinder cars and six-cylinder cars separately. The sole exception is the E30 M3, which uses a six-cylinder-type differential, thus providing a source of 4.10 limited slip diffs for the 325i. In addition, differentials from the E28 5 Series BMWs (1982-88) will also interchange with the E30 six-cylinder 3 Series cars, and this becomes key to modifying the early eta engine E30s.

so i am confused as to whether i can use the 4:10 lsd from my auto 318i with the 325i engine swap.


Wrong...I know for fact, as i used a 3.91 318i diff in my 325e for about 4 years! It was a straight swap, bolted right on...and it takes the abuse of the 6 cyl.*th-up* Best mod i did!

new2bmw
11-11-2009, 02:11 AM
so take everything from the 325i except the diff and put it on the 318i, and use the 4:10 that was originally on the 318. i am now reading stuff about small case , large case etc, also does it matter if a diff goes on an automatic or manual car? or does the tranny type have nothing to do with it?
thanks for all your info, great help!

Mystikal
11-11-2009, 06:45 PM
I know 5-speed '84 318s had 3.64 diffs up to 11/83 build, and 3.91 after that.

The 318 will have a small case diff, I wouldn't personally put that on a 6.

craz azn
11-11-2009, 07:31 PM
As long as you don't do repeated burnouts, doughnuts, etc, the small case diff will be fine in the 325i.

NOTORIOUS VR
11-11-2009, 11:16 PM
^^^ Even if you do the small diff is fine. My buddy put 400rwhp though his stock 2xx,xxxkm diff and it's still alive after more then a year of abuse.

Ceeker
11-12-2009, 12:07 AM
The stick325i has a 3:73 and the auto has a 4:10; at least the ones I owned. so if you got a 318i with a 4:10 it won't make any diff. pardon the pun

craz azn
11-12-2009, 12:31 AM
^^^ Even if you do the small diff is fine. My buddy put 400rwhp though his stock 2xx,xxxkm diff and it's still alive after more then a year of abuse.

True true, just preparing people for the worst. A lot of people love regurgitating some internet myths that small case diffs immediately blow up once it is in a 6 cylinder powered car. Which is not the case.

Now people who kill medium case diffs with stock, or relatively stock e30s... :D What are those guys doing behind the wheel LOL.

E30M42cab
11-12-2009, 07:16 PM
^^ The question is; how did I kill my small case 4.27 with my M42??? WTF!!

new2bmw
11-12-2009, 10:25 PM
i thought it was a 4:10 in the auto 84 318i but everyone is saying something different. anyways if it is a 4:10 and the 325i has a 3:73 what difference would it make between the 2 with the m20 engine? I am wondering if it will even be felt? i guess i probably want to go with the one that has the highest ratio for better take off?

Mystikal
11-13-2009, 08:06 PM
^^^ Even if you do the small diff is fine. My buddy put 400rwhp though his stock 2xx,xxxkm diff and it's still alive after more then a year of abuse.

And I know a guy with 198rwhp who murdered a small case.

Fact is no one here has enough data to truly make a statement on it, but in my opinion, there's a reason BMW made 2 different diff sizes.

NOTORIOUS VR
11-14-2009, 12:33 PM
And I know a guy with 198rwhp who murdered a small case.

Fact is no one here has enough data to truly make a statement on it, but in my opinion, there's a reason BMW made 2 different diff sizes.

I get what you're saying... but these are old cars and many people here are the 3+ owners and know nothing about how they cars were maintained/treated.

Obviously the larger diff will be able to handle more power/abuse, but it seems the small diff is also very capable. *th-up*