Limited Slip Diff

Mon Feb 14, 2005 7:06 am

Please, please can anyone help. I recently bought an 1989 320i Convertible and I have a noisy diff. I want to change this and am thinking of upgrading it to a ltd slip diff off a 325i. There seems to be two types of diif ratio, 4.10 & 3.91. Which is better for performance and why? Oh, and can anyone recommend where I can get hold of one that aint going for an arm-and-a-leg in London!!!!

Mon Feb 14, 2005 7:53 am

3.91 and 3.64 are the most common in limited slip diff form, the 4.10 has only recently been talked about - these are very rare.

Your cab could well be running a 4.10 open diff I'm not sure, but the the lower the ratio number equates to higher gearing. The 3.64 would be better for motorway miles for example, personally not having driven the 3.91 or 3.64 I can't tell you if there's much difference in a 0-60 sprint.

These usually start at Ãƒ”šÃ‚£200 a pop if they come up on here, best bet is a local scrappy mate who charge half of that!

Mon Feb 14, 2005 9:02 am

I have a 4.1LSD, I changed from I think a 3.25LSD, and I didn't really notice any difference in acceleration. I got the diff at the same time as my full exhaust with headers and I took about 1sec off my lap times at the race track, but it didn't feel much different. So I wouldn't really worry about getting a 4.1, the 3.91 or even 3.64 should be ok.

Aston

Mon Feb 14, 2005 9:03 am

My car was factory fitted with a 3.73 LSD, and I've just changed it for a 4.10 LSD.
Far better for accelerations

But not so good for fuel saving

Ps: my 4.10 is noisy too

Mon Feb 14, 2005 10:15 am

Mine is a little noisy on light or no throttle, like if I am driving at a constant speed and then back off. All the parts in my diff were reconditioned though and sent away for lapping so there is definately nothing wrong with it. The mechanic that fitted it said that all Motorsport LSD are a little noisy, and he has a Motorsport LSD in his S14 engined E30 race car.

radback: You noticed a difference in acceleration? Was it much?

Aston

Mon Feb 14, 2005 12:09 pm

wheres every1 getting there 4.10 LSD's from ive been after 1 for ages now and still not found 1 unless its going for loads

Mon Feb 14, 2005 1:17 pm

Astong is based in Australia but not sure how a 4.10 made it's way out there! Radback is in France I think so I imagine a few 4.10's trickle over from Germany.

Tue Feb 15, 2005 1:58 am

thanks for that jimbob
any1 wana sell a 4.10 lsd pls let me know how much and where you are

Tue Feb 15, 2005 9:29 am

gorgeee wrote:thanks for that jimbob
any1 wana sell a 4.10 lsd pls let me know how much and where you are

Very, very hard to find mate, 4.4 is more readily available but still pretty scarce, 3.9 is no problem tho'.

Tue Feb 15, 2005 12:38 pm

yeah ive found a 3.91 but still want the 4.10 Lsd
your name m3compact is that mean youve got a m3 in a e36 compact?

Tue Feb 15, 2005 5:48 pm

gorgeee wrote:yeah ive found a 3.91 but still want the 4.10 Lsd
your name m3compact is that mean youve got a m3 in a e36 compact?

Building one for Stage Rallying.

Original intention was to use E36 M3 Evo drivetrain, now using E30 M3 S14 for weight distribution reasons.

With a 4.45:1, 75% twin plate LSD diff'.

Tue Feb 15, 2005 9:39 pm

gorgeee wrote:yeah ive found a 3.91 but still want the 4.10 Lsd

I don't know if there is much difference in performance between those 2 and the 3.91 will be slightly more comfortable on long journeys. I think just having a LSD will give you enough traction that you will probably still accelerate just as fast a 4.10 non LSD, especially in the wet or on a loose surface. Definately look for a 4.10 LSD but if they are as rare as everyone says it might be better just to get a 3.91

EDIT: Also if you have a 4.10 non LSD you could try a place like this http://www.bmauto.iinet.net.au/parts.html they say "Will build any diff ratio to LSD for any BMW. You can supply your own diff! AUD$550
(no warranty on crown wheel & pinion)". Obviously that is in Australia but I am sure you have places like that too.

Aston

Tue Feb 15, 2005 11:01 pm

EDIT: Also if you have a 4.10 non LSD you could try a place like this http://www.bmauto.iinet.net.au/parts.html they say "Will build any diff ratio to LSD for any BMW. You can supply your own diff! AUD$550
(no warranty on crown wheel & pinion)". Obviously that is in Australia but I am sure you have places like that too.

http://www.e30zone.co.uk/modules.php?na ... pic&t=2562

Wed Feb 16, 2005 1:21 am

astondg wrote: radback: You noticed a difference in acceleration? Was it much?

After the 3.73, the 4.10 (both are LSD) make a sensible difference (more than a chip change) but of course my BMW didn't changed in a dragster. :lol:

The car feels more nervous with a better response, lighter.
This is a very good mod if you don't use Highways too much.

PS: 4.10LSD are also rare in France. Best place to get them are Germany (some 318IS small casing) or USA (M3 E30 big casing). Mine is small casing and was fitted on a 320.

Wed Feb 16, 2005 1:32 am

yeah i found 1 on ebay this week in germany and bidded 260 on it but werent able to get to a pc to up the bid
anyway that diff has 320i in chalk on it and that made me wonder?
im thinking of using a 318is LSD as im not going to be giving it lots of abuse just the odd bit now and then and just want my touring to feel lighter once i got my 16"s on it and so on.just want the LSD for the now and then i do give it some

Wed Feb 16, 2005 10:07 pm

ive been offered a 3.25 ratio lsd small case, from an e30 323. didnt think these existed. does any one know how much talk these small case diffs can handle? is 400Ibs of torque to much through one?

Thu Feb 17, 2005 11:10 am

nigel79 wrote:ive been offered a 3.25 ratio lsd small case, from an e30 323. didnt think these existed. does any one know how much talk these small case diffs can handle? is 400Ibs of torque to much through one?

Yes, 400LBS is deffo too much for a 168mm CWP.

Are you sure it's a small case LSD from a 323?