Re: poly trailing arm bushings

[AKress1948@domain.elided]

Bill is correct, the trailing arm bushings available today are quite soft, 
slightly firmer perhaps,  but basically equivalent to the OEM rubber pieces.  

the trunnion arm is tasked w/ most of the side to side location of the car 
over the rear axle (including body roll), as well as keeping the diff from 
rotating around the axle.  The roll itself is, of course, countered by the 
springs and sway bars.
the trailing arms are there to locate the axle mostly in a fore and aft mode, 
i.e. they are asked to work mostly in compression and tension.  They are the 
ones that take the throttle inputs, and shocks (in and out).  Their design 
and the design of their mounts are well suited to that task.  In corners, 
since the axle stays (mostly) parallel to the ground, but the car leans, 
there is a requirement for these joints to allow some radial displacement as 
well.  IMHO, everyone is right here - this is not the place to add roll 
stiffness to the chassis.  Heim joints, or the rubber or poly in the bushings 
allow this movement and reduce to varying degrees the movement of the axle in 
the "longitudinal".  My guess is that this radial movement is distributed 
over the joints at both ends of the trailing arm.  I'd also guess that the 
axle end takes most of it.

the key advantage these polyurethane parts have over OEM is their longer 
useful life.  the rubber in the oem parts degrades pretty quickly (no not in 
days!!!), while the poly is pretty inert.  The net effect here is that the 
car's handling stays constant and matches the designed behavior for a much 
longer period of time.
BTW, i think the the driver side forward end bushing failure Bill refers to 
is probably due more to resisting throttle inputs than cornering roll.
Andy  
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