Differential question

[erik325i]

Not trying to hijack, but was there a non-viscous 3.91 large case LSD offered on any cars? I think it would be a good compromise between 3.73 and 4.10. I imagine I could cannibalize an ix diff for the ring and pinion, and have it swapped in to a 3.73LSD, but I would rather just do a straight swap.

Why don't you want to just use the viscous ix LSD? What makes the clutch pack diff any better?

-Erik

[Digitalwave]

Not all automatics had an LSD, even if it was a 4.10. I don't think all 325iS's had LSD's either.

[silversleeper]

5spd? All US RWD manual 325i/is coupes/sedans had a 3.73

are you telling me that my 89 325iM sedan has a 3.73?

from what ive read so far, all cars were not created equally. i really need to get under my car and check. can anyone tell me where to look?

[Digitalwave]

are you telling me that my 89 325iM sedan has a 3.73?

from what ive read so far, all cars were not created equally. i really need to get under my car and check. can anyone tell me where to look?

It should have a 3.73 open.

[kmack]

Yes,

noticeable for sure. I installed this in my previous car, 5spd 90 325i.

The bad part is your 1st gear revs out pretty fast and highly cruising rpms are higher, but who cares right?

I just finished this swap yesterday: 4.10 LSD (from '90 318is) into my '87 325is. Originally, it had a 3.73 LSD, but I had it rebuilt last year in August (bearing failure) and the bearings started going again back in June.

Lots of acceleration in the lower gears and plenty of passing power without having to down-shift (unless you REALLY want to pass). Added about 500-800 rpms to my highway speeds.

Gotta question, though. I left the speedometer pickup for the 4.10 in the case. My original from the 3.73 was a little busted up but appears to still be workable. Which would be better to try and keep my speedometer correct?

My thinking was to keep the 4.10 pickup because it would be set for the gear ratios. I have noticed that my speedometer is off (reading high). Any ideas?

[nando]

the pickup doesn't matter- they are the same, the gear ratio doesn't have any effect on it. there is a plate inside the diff with "teeth" that the pickup reads and translates into your speed.

[kmack]

I checked the plate inside before I installed the new diff. Both differentials have a plate with the same number of "teeth" on it. Each one had ten. But I did not check to see if the size of the teeth were different. Would that matter?

In driving the car now, when at highway speeds, (speedlimit is 70) I'm keeping up with traffice in the right lane, being passed by faster drivers in the left, and my speedo is reading about 80 mph.

Before the swap, I do know that my speedo was about 3-5 mph fast. It seems to read faster now. Not that that is a problem, I drive too fast anyway.

[manolet01]

Would you know if there was an LSD with a 3.91 ratio? The VIN on my car showed that I should have LSD. I just bought a Euro 325i and I'd like to check if it still has the original diff.

Thanks!

[kmack]

I know someone that just bought a 3.91 LSD for their 325is. They didn't get it from a salvage yard so I don't know what exactly it came out of.

As for mine, the car was an absolute blast to drive. Great acceleration, plenty of passing speed, 1st gear was almost useless, but still very fun, and great for an autocross course.

Unforntunately, we have sold it. Just over 310k miles is a bit too much for me to keep up with maintanence-wise. Car still runs strong and is very reliable. I know the new owner will enjoy it. I already miss it.

[ZinRot325i]

Would you know if there was an LSD with a 3.91 ratio? The VIN on my car showed that I should have LSD. I just bought a Euro 325i and I'd like to check if it still has the original diff.

Thanks!

If you want to know if it has an LS diff just jack it up and spin the wheels. If they both go the same way, especially if you have a friend apply resistance to the other wheel, it's a limited slip.

That or do a burnout and if you leave two skidmarks, it's a limited slip.

[erik325i]

Would you know if there was an LSD with a 3.91 ratio? The VIN on my car showed that I should have LSD. I just bought a Euro 325i and I'd like to check if it still has the original diff.

Thanks!

Yes, the manual 325ix cars came with a 3.91 Viscous LSD.

-Erik

[manolet01]

Thanks for the feedback guys. Much appreciated. I already tried spinning one wheel when the car was up but the other wheel spun in the opposite direction. Will an LSD behave this way without any resistance on the other wheel? Or does this mean I already have an open diff?

[Digitalwave]

Thanks for the feedback guys. Much appreciated. I already tried spinning one wheel when the car was up but the other wheel spun in the opposite direction. Will an LSD behave this way without any resistance on the other wheel? Or does this mean I already have an open diff?

Sometimes mine spins the other way even though its an LSD. Just check the tag and see if there is an S on it.

[manolet01]

Got it. Thanks! :)

[erik325i]

Sometimes mine spins the other way even though its an LSD. Just check the tag and see if there is an S on it.

Is your diff worn out? It shouldn't spin the other way at all, even if you try.

-Erik