goatherder

SO...I know the basics: I know that the purpose of these tings is to act as a pivot for a suspension arm... and also to isolate road noise. And I know that Poly bushings act different and transfer more NVH into the chassis. But here's the thing; I got to looking at these control arms with the bigass Moog bushings in each end and it got me wondering about what these things actually do when the suspension is working.

A bushing assembly consists of a steel cylinder, with a rubber cylinder inside that...and another steel tube inside THAT...which is what the bolt goes thru. These three parts are all bonded together. Then this bushing assembly is sandwiched between two "mounting surfaces", the bolt is slid thru and then torked to XX ft/lb. (85 on the lower control arms)...which is fooking tight and will compresss the mounting surfaces into the sides of the control arm bushing. Seems the resulting friction would bind up the joint and make it not want to pivot. Which would seem counter-productive. Seems a better plan might be to tighten the pivot bolts just enough to eliminate any slack and call it good. Maybe use a lock nut or something.

What am I missing here?

SuperRA

The bolt clamps the inner tube tight to the chassis (for example, it can be reversed in some cases) and the outer shell is pressed into the suspension arm. Basically the tube is one with the chassis and the outer shell is one with the control arm (or other suspension component). The way that it pivots is...... the rubber flexes. The rubber just twists back and forth in it's shell. That's why the bolts should be torqued in an at rest position so the rubber is not twisted at rest. And as an added plus, the rubber dampens extra vibrations.

Poly bushings work differently as they actually pivot. They are lubed and thus pivot on the inner tube and possibly inside the outer shell.

If that tube were not tight as you are suggesting, it would wear out from rubbing metal on metal in no time. Since the rubber is so compliant, it takes a while (alot of movement) to wear it out. Stock suspension doesn't normally move all that much which the flex of rubber provides enough movement. Think of a rubber band, how long would it take you to break a rubber band by stretching it (within it's capacity) and releasing it? Probably a long time. Yeah it'll get weaker and weaker, but it will still stretch many times for a long time.

Anyways, that's my take.