Differential Bushings, what's the difference?

[CorvallisBMW]

Hey guys, I'm looking for some info on the various types of diff bushings out there.

I was under the impression that the "solid" OEM Z3M bushing was an upgrade over the standard e30 bushing. RealOEM lists it as p/n 33172228425. But, a quick google search shows that it is not solid.


The standard e30 bushing is p/n 33171128586 and looks like this


My car already has a "solid" bushing, and looks like this, but I don't know what p/n it is.


As I'm about to add a lot more hp to the car, I want something that's going to hold up to that extra torque. Does anyone know much about the Z3M bushings vs the "solid" bushings and what kind of power they can handle?

[marshallnoise]

I can tell you that you want firmer, but not solid. I had a 99 Cobra that I installed aluminum diff bushings and the gear whine was just unreal. I would try and find a suitable poly alternative.

[88BlackS-ETA]

Try Revshift.

http://www.revshift.com/product-p/pdb-e30.htm

[Northern]

I've had a busted OEM diff mount, two 90A Polyurethane diff mount, and a 75D AKG Solid Delrin mount.

Switching from OEM increased gear whine by a bit, but switching from poly to delrin made little to no difference for me.

[CorvallisBMW]

'm going to try the 80A Revshift bushing, see what happens.

[bmwman91]

Although this thread is a little old, I came across it during some research into "stock upgrade" diff bushings. My stock E30 one is shot, and I don't want to run poly because I did that for 7 years and to be honest, at least on a street car / DD, the extra noise was annoying.

OP, the solid diff bushing you show in your photo is the OEM 325iX unit, BMW PN 33-17-1-134-802. It retails for $110-150 new.

33-17-2-228-425 is the Z3M bushing, as you noted. If I had to guess, this one might actually be slightly stiffer than the solid 325iX one because the Z3M unit has a lot of steel packed into the rubber. I would imagine that the tradeoff is that the Z3M part will be more prone to tearing since it has a lot more mating surfaces between rubber and steel.

[jeffnhiscars]

Although this thread is a little old, I came across it during some research into "stock upgrade" diff bushings. My stock E30 one is shot, and I don't want to run poly because I did that for 7 years and to be honest, at least on a street car / DD, the extra noise was annoying.

OP, the solid diff bushing you show in your photo is the OEM 325iX unit, BMW PN 33-17-1-134-802. It retails for $110-150 new.

33-17-2-228-425 is the Z3M bushing, as you noted. If I had to guess, this one might actually be slightly stiffer than the solid 325iX one because the Z3M unit has a lot of steel packed into the rubber. I would imagine that the tradeoff is that the Z3M part will be more prone to tearing since it has a lot more mating surfaces between rubber and steel.

That's interesting. That same solid bushing came off my cabrio when I swapped diff covers.

[CorvallisBMW]

^same, the new 2.93lsd I picked up, that came off a 325e, had the solid bushing.

I have the Revshift 90A bushing just hanging out, I'll probably install it this winter.

[bmwman91]

Interesting. I wonder if BMW put the solid one into a lot of cars, although it was only "officially" for the 325iX? It could also be one of those "gaps" in RealOEM where not all options are properly represented or something. Goodness knows that it wouldn't be the first example of that!

[bmwman91]

Just FYI, the solid 325iX mount (33-17-1-134-802) is on national backorder until mid-December. I had ordered one from getBMWparts and was informed of this. It happened to be that Turner Motorsport had one last unit left in stock, which I promptly purchased. So, if you want to get one of those mounts, I recommend calling the parts supplier first to see what their lead time will be. It seems like a fairly good deal to me...$50 less than the MZ3 mount and it is stiffer/sturdier than the stock E30 one.

Turner lists the mount as being for the various E30 325 models and the M3, so maybe it was a stock part on them and RealOEM doesn't show it.