91 E30 M42 differential swap options

[BlackBMWs]

Last weekend, I experienced a serious clunk, clunk, clunk after hooking a right turn from an intersection. after inspecting the drivetrain, I found the source of the clunking.



I wonder if I can just JB weld this back on.



The fresh fluid is on the right. Fine metallic particals in the current fluid along with the one big chunk.


The driveline to the diff was just fine.

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I'm checking to see what differentials folks have swapped into their M42 E30s. I did pick up a non-lsd 4.10, but wondering if it's worth looking for a LSD in either a 3.73 or 4.10 since I'm swapping and I might find a suitable donor in the area.

I use my vert as a DD when it gets warmer and much of my driving is on the freeway, so a 3.73 or lower number ratio would drop revs on my normal drives, but don't want to make a siginifant performance difference. I normally run at 3500-4000 rpm on my current 4.10 on the freeway and about 21 MPG. (top down)

I'm interested in hearing M42 experiences as far as the range of differential ratios and type (LSD vs non-LSD) folks may have put in and their satisfaction with their choice.

Just asking... Thanks!

[xwill112x]

i swapped a medium cased 4:10LSD into mine and love it

[xwill112x]

and yes, LSD's are worth it.

[twistednut]

A 3.73 LSD is perfect for the m42. 70 mph is right at 3k rpm. You only getting 21mpg indicates you have one or more vacuum leaks under the intake.

[BlackBMWs]

A 3.73 LSD is perfect for the m42. 70 mph is right at 3k rpm. You only getting 21mpg indicates you have one or more vacuum leaks under the intake.

Thanks! On the vaccum leaks, I swapped every cooling, vaccum and fuel hose and intake gasket last year. I was actually attributing the mileage to pulling higher revs on the freeway, top down. I'll check it out.

I'll seek out a 3.73 LSD this weekend. Are any installation modifications needed to replace the 4.10? Swapping 4.10s was straightforward... Thanks!