from 3.73 LSD + open 3.45 to 3.45 LSD

[IlovM42]

Hello people.

I have a technical question concerning differentials.

I actually have on my car a 3.73 with limited slip, problem is that there is a bad bearing on it :curse:
I also have a 3.45 open diff and an E36 gearbox laying in my garage so my plans are to bolt the E36 gearbox to my M42 and use the 3.45 diff ratio with the LSD system.

So my question is, what is the most simple/easiest swap i can do, swap diff internal i mean to put in the 3.45 housing, the 3.45 gears with the LSD

OR take out from the 3.73 housing the gears and put those from the 3.45 keeping the LSD...

Don't know if i'm clear and understandable. but what I want to know is if it's not more simple to keep the LSD in the same housing as the adjustment is already done to match housing with LSD.

I'm also going to change all the bearing and seals, don't going to open the LSD as it's working fine.

thanks in advance! ;)

[e30rapidic]

assuming they're both medium case e30 casings....

use the 3.45 casing so you don't have to mess with the pinion gear set up. Remove the 3.73 ring gear from the LSD unit and put the 3.45 ring gear back on it. Throw that back in the 3.45 casing.

I have an e36 zf trans and 3.46 diff behind my S50. The highway RPM's are a bit high for my taste, however with the 3.73 it would be unbearable.

[IlovM42]

Yeah didn't tell it but they are both medium case
So it's better to keep the housing matching with the gear ok. Thanks a lot

And yeah 3.73 would have been fun for a track car with the M42 and E36 gearbox but as i'm more likely to use my E30 in highway sometimes, i prefer to go the 3.45 route, as this will give more or less the same as the original setup, just a little shorter

[yeaseth]

I agree

[jlevie]

assuming they're both medium case e30 casings....

use the 3.45 casing so you don't have to mess with the pinion gear set up. Remove the 3.73 ring gear from the LSD unit and put the 3.45 ring gear back on it. Throw that back in the 3.45 casing.

While you might get away with not having to shim the the output or pinion bearings, the chances are pretty low. Assume that you will have go through the full set up for backlash, pinion preload, and pinion depth adjustment. And since you'll have to do that, it would make sense to replace the bearings.

[IlovM42]

i'm looking to change the bearing too, as i don't know what is the condition of the bearing on the 3,45 and the 3.73.

[jlevie]

In that case you will have to go through all of the steps in setting up the differential.

[MatRacer]

Just to make sure, here are two questions:

1- If I have a medium case E30 diff, can I swap the e30 gears with e36 ones?
2- Pinion is always the same, it is just the ring gear that changes?

Reason is that I will have a S50 coupled to a ZF 320 with a 4.10 fina ldrive! Way too short. Have a 3.73 laying around, but thinking about 3.45 or 3.15 from an E36...

[LivingLegend06]

The ring and pinion gears are matched to each other. They both from the same ratio differential.

[MatRacer]

All right! Thanks! What about the e30 vs e36?

[Wanganstyle]

Deleted

[MatRacer]

Regarding 3.15 and 3.45 ratios from e36, Which one came with M14 vs M12 ring gear mounting bolts?

Thanks!

EDIT: according to this http://www.realoem.com/bmw/showparts...89&hg=33&fg=15

The bolts of the 3.15 ratios of the 325is would be M12.

[Wanganstyle]

Deleted

[IlovM42]

hi guy. since this question 7 years ago the rear lsd diff actually went from 3.73 to 3.45 and last year it went back up to 3.64 with a complete rebuilt and now have 60% lock with 4 paris of disc.

[bignslow]

How was drivability with 3.45s and M42? Someone swapped LSD out of my 91' for open diff so I want to swap the LSD back in. I found a complete diff out of Z3 but it has 3.45s. My stock gears are suppose to be 4.10s. I have no idea what's in there now other than it's open diff. I am guessing not 4.10s. Was that M42 a dog off the line with 3.45s?