[Cm452]

I've an 08 335xi 6mt. The front diff, of the 3.08 ratio flavor, is nigh impossible to find. Mine whines like a tin lizzy, and revealed black, ruined fluid when I did a change so, alas, I need another one. Junkyards are telling me there is a difference between 07-->04/08 and anything after. They also refuse to warranty anything used under interchange, say, from an e6x chassis. My understanding was that any front diff from an N54 6mt e9x or early e6x would fit, and certainly wirh respect to the e9x chassis, they'd all fit.
Could anyone help clear this up?
Also, might anyone know of a better source for these things other than car-part or eBay?
Thanks so much!
-Cm

[matteblue3er]

You need to keep diff ratios the same front and rear.

I would take this opportunity to change to 3.64 or 3.91 ratios (these are auto trans ratios btw, but will work for 6mt) for better performance. You can find matching front and rear diff sets on eBay

Look on realoem.com to cross-reference part #s

[Cm452]

That has always been the fallback plan. However, doing twice the work only to have it scream on the highway is not super appealing. That said, I'd be surprised if the ECU tolerates the non MT final drive. The ecu definitely knows what gear it is in, and this is SUPER important for what maps it uses in the flash.
-Cm

[kenmar]

I would rebuild your existing diff. Any good tranny shop should be able to handle it. I had the rear diff on my old E36 rebuilt when it started to whine. No issues at all post-rebuild for almost another 10y when I eventually sold it.

[Cm452]

Originally Posted by kenmar

I would rebuild your existing diff. Any good tranny shop should be able to handle it. I had the rear diff on my old E36 rebuilt when it started to whine. No issues at all post-rebuild for almost another 10y when I eventually sold it.

That's good to know, thanks! I had considered this, however, I was told that if the ring-gear is kippered the diff is essentially toast. I suspect that the pinion pre-load is not the issue here, as it is for many, and rather the ring-gear and pinion are knackered/galled to hell. There are a couple of people on these boards who've had the same problems. When they opened up the diff the story is almost universally the same; the ring-gear is all galled and pitted, sometimes with teeth missing. Fill-welding the missing material and then machining the correct profile is going to be $$$$$$.
I hope, however, that I am wrong...
-Cm

[CDirks]

Finding diff's online is a journey, not a pitstop, in my experience too. Half the junkyards in the GBA don't respond to online inquiries.

I would also consider swapping to slightly higher ratio too. Bumping up to a 3.23 wouldn't murder your mileage. There are a few threads around where people swapped to higher ratios and were happy with the results. Maybe just see whichever is readily available/compatible and trade up? The gearing concern you mentioned is not one I've heard of before either...

Let us know if you do have it rebuilt though. I'd be interested to know what the going rate for our cars is.

[Cm452]

Woof, that ratio is even harder to come by! 99% of carriers are 3.46. I'd rather put 335i knuckles on it and chuck that piece of shit differential into the swamp from which it came than the 3.46.
Again, I'd love to know the difference between builds before April of 08 and those after with respect to the differential.
Thanks!
-Cm