General Recommendations for Rear Subframe and Differential Bushings: OE and Poly

[oceansize]

While installing my new GC ARCAs I will also be installing a 3.91 diff from diffs online.

1. Where do we stand on the varying brands of poly bushings in 2020 with regard to durability and comfort?

2. I can't remember whether most said to keep the diff bushings stock and it was OK for the subframe bushings to be poly or vice versa?

I'm not looking for race car stiffness. Just good durability and reasonable comfort.

[repoman89]

I went with Turner solids for the subframe and OE for diff, and the car is smoother and quieter than it was with 40k mile but original OE bushings all around. That was the general recommendation I saw all over m3f

[oceansize]

Hmm..I wasn't even considering solids. I take it you got these turners?

[Obioban]

Other than a full out race car (not track car), I'd stick with stock diff mounts. There's not a lot of stiffness to be gained over stock (stock is quite firm), and all aftermarket options add varying degrees of a large amount of NHV. Note: e36 bushings are softer than stock-- so by stock I mean new e46 M3 (which means a new diff cover).

Subframe bushings don't add much NHV, but there's no compromise free poly setup. If you're switching out subframe bushings, I'd go full solid. If you're at stock ride height, Turner. If you've lowered the car, CMP makes solid subframe bushings that raise the subframe, recovering geometry lost from lower the car and/or from adding subframe reinforcement plates.

[oceansize]

Other than a full out race car (not track car), I'd stick with stock diff mounts. There's not a lot of stiffness to be gained over stock (stock is quite firm), and all aftermarket options add varying degrees of a large amount of NHV. Note: e36 bushings are softer than stock-- so by stock I mean new e46 M3 (which means a new diff cover).

Subframe bushings don't add much NHV, but there's no compromise free poly setup. If you're switching out subframe bushings, I'd go full solid. If you're at stock ride height, Turner. If you've lowered the car, CMP makes solid subframe bushings that raise the subframe, recovering geometry lost from lower the car and/or from adding subframe reinforcement plates.

I am 13.25 in the rear and do have redish plates welded in. I will check out the CMP bushings.

[newton22]

I run 75D poly bushings on my diff and don't recommend it to most people. It whines like no tomorrow but I personally love it because the throttle response is tack sharp and the car feels more like a vintage racecar so it depends on what you're going for.

[Nick_P]

Is it mostly diff whine that you are adding on the NVH side, by going with solid or poly diff mounts? In the process of putting Turner's solid diff mounts on mine, from what I've read diff whine is their drawback?
I was planning on going with CMP subframe, diff mounts and RTABs, they look high quality products as others have mentioned. But once you add their VAT and shipping they get a bit pricey

[bassel_sy]

Other than a full out race car (not track car), I'd stick with stock diff mounts. There's not a lot of stiffness to be gained over stock (stock is quite firm), and all aftermarket options add varying degrees of a large amount of NHV. Note: e36 bushings are softer than stock-- so by stock I mean new e46 M3 (which means a new diff cover).

Subframe bushings don't add much NHV, but there's no compromise free poly setup. If you're switching out subframe bushings, I'd go full solid. If you're at stock ride height, Turner. If you've lowered the car, CMP makes solid subframe bushings that raise the subframe, recovering geometry lost from lower the car and/or from adding subframe reinforcement plates.

do the turner bushings raise the car as well or is that specific to CMP?

[Obioban]

do the turner bushings raise the car as well or is that specific to CMP?

That’s a result of raising the subframe... that you can fix by adjusting your ride height adjusters...

but, no.

[bassel_sy]

That’s a result of raising the subframe... that you can fix by adjusting your ride height adjusters...

but, no.

would u recommend the CMP bushings if the car has been lowered? Im not to familiar with CMP at all, but per them they are saying its good option if the car is lowered or subframe reinforced. I got my subframe checked few days ago and 0 cracks. My car is on V3s and obviously substantially lower than stock height.Worth it?

[Obioban]

would u recommend the CMP bushings if the car has been lowered? Im not to familiar with CMP at all, but per them they are saying its good option if the car is lowered or subframe reinforced. I got my subframe checked few days ago and 0 cracks. My car is on V3s and obviously substantially lower than stock height.Worth it?

If you’re going solid either way, yes.

[Tigerbimmer]

I don't recommend poly's in the diff as well. When the car was new to me over 5 years ago I had a shop do all of the usual suspect stuff under the car, AKG diff bushings being one of them per their recommendation. Diff whines over 65mph and the NVH/clunk is annoying when shifting under 3K rpms. I've lived with it all this time since I rarely drive the car but getting OE bushings installed is on my laundry list of things to do this year.

[Obioban]

The OE diff mounts are also really freaking stiff— there’s not much actual room for a performance benefit.

[roverT]

I picked solid Turners when I did my Vincebar and stayed with OEM diff bushing so there is no whine of the diff coming into the cabin of the car.

Vince taught me that a solid subframe bushing will transfer the load directly to the threaded sleeve of the mount. Poly have a separate inner sleeve with the poly on the outside so if I understood him correctly, poly load is transferred to the RACP surface via the outer perimeter poly and can never be transferred in majority to the inner sleeve which is connected to the threaded sleeve in the mount. Solids connect directly to the RACP making the subframe part of the RACP thus decreasing any load subjected to the RACP before solids.

I didn't notice any NVH increase but I did notice a faster response "feeling" from the rear which makes it even easier to react to the back end when you're spirited. It can be a bit more tail happy if you're not smooth with input but when you are meaning to do that, it'll react quicker to your input as you ask.

There is one other product that is out and my friend is also developing which is solids with delrin disks as a top/bottom side surface...looking like a flat Lifesaver candy. I'm not too up in the engineering of that yet though.

[jojo]

Is everyone recommending OE rubber for the front and rear diff bushings? (Car will be street driven- compliance is a priority). If so, any way to replace the rear rubber without having to buy a whole new cover?