Poly bushings, shim trailing arms

[Richard E.]

I am installing new polyurethane bushings in the trailing arms along with changing to stainless steel shims in my 66 roadster. How should shims be initially installed to allow the car to be driven to the alignment shop? Any suggestions are appreciated. I could have the car trailered but I prefer to drive the (approximately) 8 miles to the shop.

Thanks much for your thoughts.

[Michael W.]

Re: Poly bushings, shim trailing arms

Any suggestions are appreciated.

Since you bravely said 'any suggestions', I strongly recommend against using poly bushings in this location. The trailing arms must, by design, move freely in three axis. Poly bushings only permit free movement in one.

Although they are marketed as an 'upgrade' they are the exact opposite in my book.

[Joe L.]

Re: Poly bushings, shim trailing arms

I am installing new polyurethane bushings in the trailing arms along with changing to stainless steel shims in my 66 roadster. How should shims be initially installed to allow the car to be driven to the alignment shop? Any suggestions are appreciated. I could have the car trailered but I prefer to drive the (approximately) 8 miles to the shop.

Thanks much for your thoughts.

Richard------


Personally, I do not recommend the use of polyurethane bushings anywhere on a Corvette. The stock-type rubber bushings are better overall. Plus, they'll last longer than you're ever going to need them to last. I do agree with the stainless steel shims, though, and recommend only the slotted type.

As far as how to do the initial shimming, it's pretty much a crapshoot if you use poly bushings. All I could suggest would be to install an equal thickness of shims on each side of the bushing. With stock-type bushings I recommend installing the same shim thickness on each side of the bushings as was removed (even though new bushings are now installed).

[Richard E.]

Re: Poly bushings, shim trailing arms

Thanks much for the responses; I wish I had asked sooner. What should the expectation be when using poly in the trailing arms?, inability to align rear suspension?, premature parts wear?, poor handling?, noise?, is this a safety issue? etc.?

Possibly persons that have tried them could share their experiences?

I would appreciate additional details on the problems caused by installation of poly in trailing arms.

Thanks again for all the help.

[Michael W.]

Re: Poly bushings, shim trailing arms

It's not a safety issue per se, and a competent shop should be able to align the car with either type of bushing. The most common complaints from users are squeaks and a harsh jarring ride. Contrary to long held marketing claims, the newer poly bushings do not last as long as the original rubber equivalents. There's lots of pics around of them crumbling into chunks after only 5-7 years use

Given that the front trailing arm joint moves in three axis as the suspension rises and falls with changes in toe-in and camber in addition to the wheel moving vertically with respect to the chassis, no rigid material is suitable for this location.

OEM style bushings are an extremely simple yet brilliant piece of engineering in that the rubber member is put in torsion with suspension movement. This has the effect of limiting deflection while under load, probably more effectively than a poly bushing. There is also the benefit of it acting as a spring with an infinitely rising rate of resistance. Poly bushings have neither of these attributes.

It makes little sense to use these bushings on street driven cars.

[Joe L.]

Re: Poly bushings, shim trailing arms

It's not a safety issue per se, and a competent shop should be able to align the car with either type of bushing. The most common complaints from users are squeaks and a harsh jarring ride. Contrary to long held marketing claims, the newer poly bushings do not last as long as the original rubber equivalents. There's lots of pics around of them crumbling into chunks after only 5-7 years use

Given that the front trailing arm joint moves in three axis as the suspension rises and falls with changes in toe-in and camber in addition to the wheel moving vertically with respect to the chassis, no rigid material is suitable for this location.

OEM style bushings are an extremely simple yet brilliant piece of engineering in that the rubber member is put in torsion with suspension movement. This has the effect of limiting deflection while under load, probably more effectively than a poly bushing. There is also the benefit of it acting as a spring with an infinitely rising rate of resistance. Poly bushings have neither of these attributes.

It makes little sense to use these bushings on street driven cars.

Mike and Richard------

One other thing to note: polyurethane has been around a long time. However, no OEM manufacturer I know of uses them in any suspension application to this day.

[Keith B.]

Re: Poly bushings, shim trailing arms

Mike and Richard------

One other thing to note: polyurethane has been around a long time. However, no OEM manufacturer I know of uses them in any suspension application to this day.

That should tell you something right there.

[Richard E.]

Re: Poly bushings, shim trailing arms

Thanks much everyone, I got it. The trailing arms are not installed as yet; I will use the OEM type rubber bushings instead of poly. This is a great forum, just wish I could remember to use it more often before I make a decision!

[Gary R.]

Re: Poly bushings, shim trailing arms

Richard,
As the guys said, stock rubber is the best in this application. I use rubber bushings in all my builds, new stock arms (usa made) have them as well. The Offset arms use a poly bushing and I have never had any call backs because of them plus they have been around a long time, 1000's of arms have them now. Again I use rubber. There are also "Johnny-joints" but I wouldn't use them for a street car.

One word of advice. Not all rubber bushings are the same. I have seen them come in with the sleeves too short, the sleeve ID too small, the Bushing cups different, and bushing diameter too large. They should tap into the arm hole, then need to be compressed and staked to hold dimension. Since new bushings may,and usually do, setup differently on the thickness your original shim stack may not work. If by chance you measured the old shims and bushing thickness you can get them very close to where they were and to an alignment shop. Some of the guys here can string align the car and that would dial it in very close.

[Joe L.]

Re: Poly bushings, shim trailing arms

Thanks much everyone, I got it. The trailing arms are not installed as yet; I will use the OEM type rubber bushings instead of poly. This is a great forum, just wish I could remember to use it more often before I make a decision!

Richard------


While you might be able to get the same bushings and associated parts in the aftermarket, you can still obtain all the parts you need from GM as follows

bushings (4 required)--------------GM #3743857

plates (4 required)-----------------GM #3820418

retainer ("tubes")(2 required)-----GM #3819806

If you were to purchase all of the above at GM list price, it would cost you about 100 bucks. By the way, the plates can be reused if your old ones are in good condition.