Can't figure out what rear diff I have

[Kotty30]

I'm trying to figure out what rear diff I have without pulling the cover just wondering if anyone can help?
I have a part number I got from the local bmw dealer witch is 33101211961 they also said it says 25% by it witch they are unsure of what that means?
The car is a 1989 bmw 325i m20b25


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[reelizmpro]

For 89 325i: 3.73 manual or 4.10 automatic. 25% is the lockup percentage so you also have an LSD.

[Kotty30]

For 89 325i: 3.73 manual or 4.10 automatic. 25% is the lockup percentage so you also have an LSD.

It's a manual so it's the 3.73. Is there anyway I can make the a full LSD? (Idk if that the correct term) I'm trying to say is there anyway I can make it lock up all the time? Thanks for the info


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[reelizmpro]

Then you'd need to have the diff welded.

[Coyote_ar]

in order to know the ratio, you make a mark on the imput flange and a matching one on the case, a mark on the output flange and a matching one on the case.
spin the imput until you get a full turn on the output. then you will know the ratio.

if you weld it, it wont be a full LSD, it stops being a differential. but you will get an extremely cheap full lock.

for full lock id say you need a torsen diff. thats the only diff type that will give you immediate lock when required. that being said, you will also have full lock on deceleration aswell.
if you want more lock, you can rebuild it, adding some extra clutch disks. originally it has 2 rings, you can increase it to 3 or 4 ... that increases the lock a lot.

for what purpose you need this diff?