Author Topic: LSD large vs small cases, ratios (Read 11193 times)

Froos · « **on:** December 27, 2006, 05:05:01 PM »

Hi all, im new to the LSD's. On my car there is a 4.10 diff which is open. I dont know how to identify if it is a large or small one.

I just got back from a trip to germany where i picked up a 3.73 LSD (for very little money), I know i cant use it because the ratio will make my car drive like a dog. The reason I bought it to trade it for a a 4.10 LSD over where I live.
But the seller told me that usually all LSD's are of the large case type, is this true?

If this is true, what is involved in using large case on a car which used to run small cases?Different output shafts maybe?

Ive added some pics , first is the old, second pic is the new one

Gunni · « **Reply #1 on:** December 27, 2006, 05:56:14 PM »

LSD�s are not big in general, it�s all model dependent,
a big E30 diff will have two bolts on the bottom side where the aluminum bolts to the diff housing,

left - small
right - big,

you can see the single bolt in the small one and two in the big one

e9nine · « **Reply #2 on:** December 27, 2006, 06:14:00 PM »

To be technically correct - there's 3 sizes: Small, Medium and Large.

Our 318 e30 cars have the small case.
The 6 cyl e30 cars and the e30m3 have the Medium case.
E38s etc have the Large case.

I know for sure the small and medium cases came with LSD. I am not too sure on the big cases.

Froos · « **Reply #3 on:** December 27, 2006, 06:33:42 PM »

Ok i went to the garage and I bought a medium size diff, can I just swap it with the small one without buying new parts?

Vladi · « **Reply #4 on:** December 27, 2006, 06:36:19 PM »

Speaking only about E30's there are two case sizes. The small one, like you have on your car and the big one which is the LSD you bought.
4.45 , 4.27 , 4.10 , 3.91 are in small cases.
3.73 , 3.64 , 3.25 , 3.23 , 3.15 , 2.93 , 2.73 are big cases.
There are some rare 3.91's in big cases. Big case diffs are used on 6cyl (320,323,324,325) and the small ones in 4cyl.
My oppinion would be to keep the 3.73. There isn't such a big difference if you'd stick a 4.10.
And yes, if you now have a small case diff you can fit a big case one plug and play and vice-versa.

Froos · « **Reply #5 on:** December 27, 2006, 06:45:48 PM »

Quote

And yes, if you now have a small case diff you can fit a big case one plug and play and vice-versa.

Excellent! Many thx guys!!

e9nine · « **Reply #6 on:** December 27, 2006, 07:36:06 PM »

I personally know of a person who wasn't able to get a diff from a 6 cyl e30 to fit in a 4 cyl e30. I have also heard of cases where the half shafts supposedly don't always fit and vice versa. My guess is it comes down to the exact year of the car in question.

Your 4.10 LSD should be fine though.

nickmpower · « **Reply #7 on:** December 27, 2006, 09:01:21 PM »

I just put a medium case 3.46 from metrix motorsports in my car, it seems it all fits

Froos · « **Reply #8 on:** December 28, 2006, 09:20:16 AM »

Quote

Your 4.10 LSD should be fine though.

Thats the thing I dont have one

silverblades181 · « **Reply #9 on:** December 28, 2006, 11:18:32 AM »

I'd like to know why everyone wants lower gearings. The power in the M42 is situated between 4000 rpm and 6000 rpm (stock anyway) so you want it to rev higher quicker. Maybe I'm missing something?

asubimmer · « **Reply #10 on:** December 28, 2006, 05:33:35 PM »

I am picking up my 3.73lsd med case tommorro. I want it for the turbo^^

nickmpower · « **Reply #11 on:** December 28, 2006, 08:05:06 PM »

i put in the 3.46 cuase i have an e36 tranny. 1st gear will be longer (better cause my light weight flywheel) and the rest will be shorter!

AL GReeNeRy · « **Reply #12 on:** December 28, 2006, 08:25:53 PM »

most of the information above seems correct, but i have a few corrections...

i believe the 4.10 also came in the e30 m3 and was a med or large case.

it also came in automatic 325i's, so that should be med or large case as well..

3.91 also came in the ix and larger cars so that could be med or large case..

Vladi · « **Reply #13 on:** December 29, 2006, 09:30:01 AM »

Quote from: nickmpower;16397

i put in the 3.46 cuase i have an e36 tranny. 1st gear will be longer (better cause my light weight flywheel) and the rest will be shorter!

what does the length of the gear have to do with weight of flywheel? Nothing, the lightweight flywheel just makes your engine rev faster. :confused:
Bentley quote for E36 Getrag 200/250 gearbox (left) and Getrag 240 gearbox (right)
1st 4.23 1st 3.72
2nd 2.52 2nd 2.02
3rd 1.66 3rd 1.32
4th 1.22 4th 1.00
5th 1.00 5th 0.81

So the 1st gear in the E36 gearbox is actually shorter than the E30 one.

romkasponka · « **Reply #14 on:** December 29, 2006, 10:42:09 AM »