Re: reply about bushings
Originally posted by crispydworst
hi thanks for every body's advice
what about all the hype with poly urethan and poly graphite. I mean every magazine form hot rod to car craft says use that stuff but im sure thay are paid too. other then the binding and bad ride does the car handle better? do the ruber bushings last longer? lets say by the down pipe will put up with the heat? im not questioning any body, I mean the way things sound im probaly going to use rubber, but do they have any pluses
thanks
Poly will not deform under load like rubber will. On components that only need to move along one axis, like the front control arms, they're great. They keep the arms moving in ways the engineers intended them to move. Rubber will smoosh under a load, and the arms will change alignment. Instead of just rotating up and down along the axis of the bushing, rubber lets them move side to side as well. This causes odd handling problems when the car is pushed.
Poly is also much more resistant to wear, chemicals, and weather. If properly installed using the usually supplied moly grease, they will last the life of the car. The passenger side rear UCA bushing, whether rubber or poly, will eventually succumb to the heat from the downpipe. Globalwest sells a greasable steel bushing for that location that will solve that problem. Just don't forget to grease it periodically.
In the rear end, the control arms have to move both up/down AND sideways. Race cars accomplish this with spherical bearings and heim joints. GM does it with smooshy rubber bushings. Poly in the back will make the car ride very stiffly, almost uncomfortably so. Because the poly will not allow the trailing arms to move side to side, the rear suspension binds up in roll. The axle can only move straight up and down.
I actually tested this. When I had poly in the rear end, I put my jack under the right side rear wheel and jacked it up. The rear axel did not roll at all. When the right side tire came off the ground, so did the left side. I put rubber back in, and when I repeated the test, the right side tire went up almost to the bumpstop before the left lifted.
You need the rear end to articulate in roll. It keeps the rear tires planted in turns (body rolls over the axle), and it also allows one tire to move up and down over things in the road without lifting the opposite side. With poly, when you hit a bump with the right side, it lifts the left side off the ground as the right goes over the bump. In quick transitions, the suspension can actually "bind," where it locks up and ceases to move at all. The springs cannot absorb the energy of the car moving up and and, and all of that force is transmitted to the tire contact patch. This amount force quickly overwhelms the tire, and it loses traction. The result is usually a spectacular spin.
Harder bushings like poly or metal will transmit more road noise and vibrations to the chassis. High durometer rubber (like GM 1LE rubber bushings) will do the same thing. If your body bushings are in good shape, you probably won't notice. I didn't when I changed my bushings out. If your body bushings are shot, then they can't absorb the noise and vibrations, so you may notice a difference.
