Do I need a poly diff mount to go with poly SFBs?

[Wishno87]

Going to be redoing the rear suspension pretty soon and I was wondering if I would need to get a poly diff mount to go with the poly subframe bushings. I know they are supposed to work in conjunction but I noticed most people don't do anything with the diff mount even when they replace everything else. I intend to use rubber for the trailing arms though.

[shoguncro]

A new OE replacement will be good as poly, because is new
i would go with OE

[shiboujin]

A new OE replacement will be good as poly, because is new
i would go with OE

What kind of logic is that?

Realistically, you should match both subframe bushings and the diff bushing. If you are running like an 80a poly, you can probably get away with rubber in the back but it isn't preferred.

Best option - match
Second best option - new oem diff bushing with soft poly subframe bushings
worst option - delrin level bushing with stock diff bushing.

[nrubenstein]

Get the MZ3 diff bushing.

[Wishno87]

Get the MZ3 diff bushing.

I was looking for this but is has some empty space around the mounting hole. Is it better than the solid e30 ones?

[nando]

on a street car? god, no. You'll want to kill yourself after a week.

definitely go for the MZ3 bushing!

80a is too soft for the diff bushing (I know, I had one, it fell apart). the stock diff bushing is already stiff! if you go up to an 80D diff bushing, it's going to be basically solid. it will vibrate your teeth out. the MZ3 bushing is perfect.

[shiboujin]

I love how you talk about things you don't understand :)

[TurboJake]

I went OEM Subframe bushings, with OEM diff bushing, and IE RTAB's.
No vibration. Nice and responsive.

But, This is the advice you want to roll with.

What kind of logic is that?

Realistically, you should match both subframe bushings and the diff bushing. If you are running like an 80a poly, you can probably get away with rubber in the back but it isn't preferred.

Best option - match
Second best option - new oem diff bushing with soft poly subframe bushings
worst option - delrin level bushing with stock diff bushing.

It's really simple to understand. Our suspension is a triangle. You don't want a weak link in it.

Even a new stock diff bushing is pretty damn stiff. You'd be amazed what new OEM stuff clears up and what it feels like.

[nando]

I love how you talk about things you don't understand :)

dude, fuck off. I've had several differen't styles of subframe bushings as well as several rear diff bushings. does your fucking hack job dorifto rolling parts car run yet?

[shiboujin]

It's really simple to understand. Our suspension is a triangle. You don't want a weak link in it.

Even a new stock diff bushing is pretty damn stiff. You'd be amazed what new OEM stuff clears up and what it feels like.

+1

My point is that you want to keep the stiffness of the subframe bushings and diff bushing as similar as possible. Otherwise, your diff will pivot and bend in ways it shouldn't and cause driveline problems. It's doubtful but it's possible.

dude, fuck off. I've had several differen't styles of subframe bushings as well as several rear diff bushings. does your fucking hack job dorifto rolling parts car run yet?

<3 you

80a is technically stiffer than the stock rubber mounts. If they fall apart, it's a matter of quality and not the material itself.

I have also run several different types of bushings in the rear end. I noticed more vibrations being transferred to the car (like road noise) but the ride is not noticeably harsher. That's more of a function of your tires/springs/shocks than the bushings themselves.

Here's a fancy chart:

[nando]

theoretically, yes. in reality, the MZ3 bushing is stiffer than many 80a bushings. The problem with a softer poly diff bushing is it will deform over time. it also doesn't really have a solid enough core to hold up to the mounting bolt over a long period of time.

I've had:
new stock OEM bushings
powerflex bushings
IE bushings
AKG bushings

the old green IE subframe bushings were best (best quality, not too stiff), none of the diff bushings were wortwhile except the 75D AKG, but it was way too harsh on the street (not ride quality but vibrations). I've put 100,000 miles on IE trailing arm bushings (no squeaks, ever), about 60,000 on an 80a diff bushing (that deformed eventually). Out of all the diff bushings the MZ3 is definitely the best for a street car. I'd keep the AKG one if I didn't have to live with it every day.

there's no law that says you have to have a poly bushing in the diff if you have a poly bushing in the subframe. It's a nice theory. But again, the stock MZ3 bushing is just as stiff as most aftermarket urethane bushings while being far better quality. it's not just rubber - it's got a steel insert that makes it more solid than a standard rubber bushing. There are also other durometers of rubber..

[shiboujin]

I very much agree. If he's running a 75D subframe bushing set, the diff bushing should be around the same stiffness.

I have no experience with the MZ3 bushing itself so I can't confirm or deny it will work in this application.

and yes, rubber is covered in the chart above. Although it might go by a different measurement name as well. Kinda like inches and centimeters are both measures of distance.

[nando]

the MZ3 bushing is likely the stiffest rubber on that chart in addition to having a steel insert. an 80a subframe bushing is definitely softer (that's exactly what I have now). after swapping the IE subframe bushings for AKG I wish I'd have just left the IE (just slightly stiffer without being too harsh), but they're OK for now. I'm just keeping them on the shelf for the next time I have the subframe out. (ugh).

[Wishno87]

So you mean the "MZ3" is better than stock E30? This confused me.

MZ3


Stock E30

[shiboujin]

*shrugs* I prefer 100% solid aluminum lol.