> Here's a question: does Smith, or anyone else offer a hard rule as to whether
> poly bushings should, or should not have steel sleeves, as the rubber bushing
> have? Seems they'd be good for reducing wear.
Smith only comments about "real race cars", and real race cars have
spherical ("rose") joints in the suspensions. That said...
I believe that poly/urethane/nylatron/synthetic bushings should
always have a bearing surface that is smooth. In most cases, this
means that there needs to be a bolt holding a steel sleeve, which
sleeve's OD provides the bearing surface (use lube!). There are
some cases ( am thinking immediately of the upper inner A arm
joint on a TR4A-6) where the stock mounting piece already has
a smooth bearing surface, and such a metal sleeve is not needed.
Remember, for the most part these bushings are replacing a rubber/steel
"metalastik" bushing. In such a bushing, there is a steel sleeve
surrounded by and bonded to a layer of rubber. The rubber is compressed
and forced into the opening in the suspension component.
When the suspension moves, the rubber flexes. It doesn't rotate in the
opening in the suspension component, and it doesn't rotate around the
bolt. This flex contributes (in a small way, and non-linearly) to
the overall wheel rate of the suspension.
The rubber component of these bushings are also capable of taking up
a small amount of fore/aft displacement to the suspension.
All these aspects of the bushing must be taken into acount when
replacing with a different material. Bolts do not, in general, provide an
adequate
bearing surface. Bolts are good for clamping or supporting shear loads.
The replacement bushing sets provide a steel sleeve to provide
the bearing surface. The bushings are a slight force fit into the
suspension arm, so that the sliding interface is at the bushing OD.
The bushings usually have a "top hat" shape, to provide fore/aft location.
Since the bushings are, for the most part, non-flexible (this is why
we're using the harder materials), this form of location is necessary.
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