Rubber -v- Polyurethane... or hybrid?

This got bandied-about quite a while back, but I couldn't locate the thread...

Polyurethane does not flex at all or very little anyway and most of the suspension parts on the era cars being restored by us are put together with rubber that absorbs impact such as from cracks in the road for example and certainly bigger and other types. Polyurethane will transmit those impacts through to the body of the car. Any movement of the suspension parts is cushioned by the rubber pieces much of them having been vulcanized to the bushing or what ever it is encased in again absorbing the stress and cushioning the impacts to the rest of the car. The polyurethane does none of that, if you put I together correctly it rotates, and if wrong will not rotate and the part it is in try's to flex instead causing stress or potentially can cause stress. That is why the suspension stiffens up and the ride becomes jarring and noisy. You could if you wanted to get rid of the polyurethane and machine aluminum pieces to go in and they will have just about the same effect.
AMC's front suspension depends on the cushioning affect of the rubber, 'specially the lower control arm. Now I am speaking of the 1970 and up ball joint cars. I have never owned something with a trunion and for a reason. But I suspect their lower control arm has the same flaws.
Of the some 2 dozen or so I have rebuilt, the lower control arm is prone to damage at the pivot point in part because of the non linear twisting motion it goes through and the rubber bushing allows that to take place, and putting in a polyurethane piece forces the lower control arm to flex even more as it pivots.
I won't use a Polyurethane piece unless there is nothing available and then there is no choice, polyurethane is machinable and parts can be made from it for a multitude of applications of which nothing else can be found. And I have done so over time.
Tom J has probably experimented more with Polyurethane front suspension pieces on early trunion equipped AMC cars that any one I am aware of over the years.

I have mixed the strut arm bushings with rubber in front and poly in the back. I should do that with my Eagle wagon too, but I'll be lucky to just get the parts swapped now.

WesternRed wrote: Seems like the rubber strut rod bushings might be out of production, Moog appears to have dropped all AMC stuff and I'm not sure if anybody else makes the strut rod bushes. The other rubber bushes are still available from other manufacturers.

NAPA NCP274-9054  (Machine strut)

Don't forget to use the special grease. I'm into poly.