Poly rear diff housing bushings bad for handling?

[NASTY GN]

I'm rebuilding my rear and bought some polyutherane to go in the ears of my housing, I just read something that the binding of the poly will destroy performance and actually become dangerous for an auto-x car. Anyone have any experience with this?

[UMI Tech]

Hey Nasty.

It's generally accepted that the GM 4-link has a tendency to bind and that poly bushings can contribute to said binding. While rubber allows geometry changes (negative) it can also reduce binding (positive).

Our solution at UMI is to build upper trailing arms, and lowers for that matter, with a Roto-Joint or rod end on the chassis mount side.

The Roto's are a street solution to rod ends short life span. When the uppers are built with a poly on the rear tabs and a Roto/rod end on the chassis, the diff housing is free to move about the suspension axis without so much binding.

http://www.umiperformance.com/catalo...roducts_id=373

We have some pretty good autocross results reported with these arms and are building a G-body now with these plus a Pro-Tour style rear sway bar.

ramey

[NASTY GN]

Thanks Ramey, I have your products, the bushings,uppers and lowers, I know my lowers are half roto half poly, not sure about the uppers, I ordered these a year ago and am finally installing now lol.

[UMI Tech]

It's important to note that properly greased and moderately torqued poly in all locations is still a good setup for general use and is certainly much better than worn out rubber. Many autocrossers with GM 4-links are all poly.

We won lots of oval track races on all poly by keeping the faces greased and by not overtorquing. If you are all poly, just follow the "keep it greased and don't overtorque" rule and you should be fine.

ramey

[NASTY GN]

I do have the roto uppers. Should I go stock rubber in the housing ears over the poly? Any other options?

[UMI Tech]

Hey Nasty. My personal preference were it my car, would be poly/roto.

Here's a good test. Raise the car and let the rear sag so you can get the springs out. With the rear hanging down in full droop, lift one side up into the wheel well. With poly/roto you'll be able to see how smooth it can travel even at such a severe angle. Chances are you'll never see that much split in normal operation. If you do, you're in trouble anyway!

When doing this, please make sure you use jack stands and follow proper safety precautions.

We did that test on our stock car and could get that articulation with the poly/poly I mentioned above. Throw the Roto-Joint in there and you should be good to go.

ramey