Ok, I was looking at the underside of the zed today ( as I do most days :stupid: ) and was looking at the upper rear control arm bush mounts, the ones that hold the bush/control arm captive. It is a sandwich between the diff mount and the underbody if you get what im talking about.

Anyhow, the circular cutout in both the underbody and diff mount is nice and smooth and this got me wondering if this needs to be. Do the bushes need a smooth mounting, do they need to be able to freely rotate?

I amp repainting the underside of the car soon with brush on POR-15 and sound deadener and this will not provide the smoothest surface, even if i dont use the sound deadener on this point, the por will still be slightly rough.

Sorry if this is a stupid question, but you do ponder a lot of stupid issues when your suffering cabin fever from being flat on your back sandwiched between a car and the ground for several hours cleaning of 30 year old underbody paint/deadener.

They don't need to be smooth on the inner control arm mount as the clamps will provide an interference fit and hold the outside of the bushings quite firmly. If you look when you remove the control arm at the original bushings you will notice they are formed to the shape of the mounts and clamps. The control arms will pivot on the inner part of the bushing with no trouble. Actually, if the outer mount were to not hold the bushings, they would surely chew themselves to piece on the mount.

The large bolt that goes into the end of the control arm serves to expand the bushing so it will then be a friction fit inside the mount.

Don't worry about putting POR-15 inside the mount, it won't hurt a thing.

Thanks for that, it was actually the facts that the original bushes had worn through the undercoat that got me thinking in the first place but what you say makes sense.

No doubt I will come up with a new riddle to ponder when I spend all monday wedged under the car again.

Those bushes don't rotate at all, they are sandwiched on the outer surface while the inner metal bush, which is bonded to the rubber, locks at each end. If you remove one of the large (24mm spanner?) cap bolts at either end you will see how this is done.

Suspension arm travel therefore depends on the rubber itself flexing. Which is why, when the bushes are replaced and the cap bolts tightened, the suspension arm should be in the normal static load position.

Which is why incidentially the OE rubber bushes are the best option in such a design. Urethane does not stand up to the twisting such a bush has to bear near as well.

Thanks, sounds like rubber is a winner.