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Polyurethane and you

    By: Yoshi Jeffery

    One of the first maintenance/upgrades performed on used cars tends to be bushings. Most drivers upgrade from rubber to a polyurethane bushing. But be careful! Not all polys are made alike.

    Below is an example of a durometer hardness scale for different types of materials used for bushings.

    Image from http://www.plasticsintl.com/

    In short, there is more to a bushing than the material itself. Within polyurethanes there are different types of stiffness. The most common bushings are 80A, 90A, and 75D.To figure out about the stiffness, the scale breaks down into A, D, and R. This means that 75A and 75D are very different materials. 75A will feel like rubber while 75D feels like a hunk of plastic.

    Your average Rubber mounts will be around 60-70A on the stiffness scale. 80A is a decent upgrade while not making the car too loud/harsh to drive. 75D (usually a material called "Delrin") is basically a solid mount and is considered "self lubricating" The material itself is slick to the touch and hard as solid plastic.

    General guidelines say to use 80A range if you are running a street car. My personal preference (for a track car) is to use solid aluminum bushings for anything that doesn't rotate and 75D for anything that rotates on a single angle. Preferably, if the joint moves in more than 1 axis, you should get spherical bearings as delrin and poly will deform and bind under harsh conditions. If spherical isn't an option, delrin (75d) is a better bet for it's lubrication properties. It's also helpful to grease the bushing when it goes in.

    Before picking a bushing, think about where it's going to go and ask yourself the following questions about where the bushing is going to go.

    For example. A subframe bushing does not move. So if it's a race car, you want solid aluminum.

    If you would like clarification on anything or want to yell at me, please email me at yoshi@slidewaysonline.com