Differential Housing Covers Difference

[Chilezen]

I see this detail skipped over whenever this comparison is mentioned, almost as if nobody knows. Or few do but don't mention it.
Even within the 24v swap community, I don't recall this mentioned... but I haven't read through every thread, so sue me.

I thought I'd make its own post about what I found when doing my own swap, which has nothing to do with the swap.

Differential covers have different thicknesses when it comes to the speedo sensor. I found this when trying to install my early-model 3.73 speedo sensor into a late-model 3.15 diff. This also becomes apparent when shopping because there are two part numbers between the generations.

Now I'm kind of dumb and didn't keep track of which one is the thick and thin one; this was a discovery I annoyingly made during my swap a year ago. So I forgot which is which. I'm pretty sure the early is thicker.. because I think the sensor hit the ring inside on the late model, thus the thinner one.

But anyway, I did want to raise awareness to anyone curious.
It's also quite possible that I am wrong about something here, that maybe can be corrected.

[packratbimmer]

This is the same with small case 168MM diffs as well. Keep in mind that the trigger wheels vary in size to match up. I have seen trigger wheels interfere with the cover.

[AWDBOB]

In my experience the diff cover/reluctor wheel changes based on ratio, not early vs late model. The change in the diff cover is to accommodate for a larger/smaller reluctor.

I believe the entire medium 188mm diff casing is different based on ratio as well, but I'm not 100% sure where the cutoff is.

IIRC the cutoff is around 3.25 gearing, IE you can't slap 3.73 gears in a case that originally came with 2.93s.

The Z3 diff covers are also different for this reason (reluctor wheel).

For example, I currently have a 3.46 diff in my e30 from an '85 model year car, with a late model 3.73 diff cover, with an early model speed sensor.

The speed sensors for early vs late themselves aren't different in length, but carry a different part number due to the plug used.

The different thickness cover needs to match that of the reluctor wheel of said diff ratio. When the correct cover is used with the correct reluctor wheel size, either early or late speed sensors can be used, in my personal experience. This may not be the case for everything though, that has just been my experience.

[Chilezen]

In my experience the diff cover/reluctor wheel changes based on ratio, not early vs late model. The change in the diff cover is to accommodate for a larger/smaller reluctor.

Holy crap, that makes more sense! I found the discrepancy when I went from a 3.73 to a 3.15... the gear size may very well be the culprit, not the year. The years were a coincidence. In fact since my 3.15 is a Z3 case.....which I was told was the same for E30's.... it's giving me a false impression on the subject.
I did have to cut and attach the new plug style in the wiring as well.

[Andre3127]

Yes, this has do with ratio rather than year. I do not know the exact cutoff of which gearsets have different offsets though.

[packratbimmer]

The more important issue is that the spool is different with the tall gears 2.79 and 2.93 for example.