Polyurethane Filled Bushes

[aragorn]

I've just got myself two new rear axle bushes for the A4, as the old ones are "slightly" worn...

I've noticed they have huge voids in the back of them, hence wondering about polyurethane filling the voids.

I've filled mounts before, but usually ones that are supporting engines and suchlike, whereas these bushes are being subject to constant twisting forces around its axis as the axle moves up and down

Just wondering if anyone else has poly-filled a bush thats being used in this type of location before?

On one hand it seems that it would make it stiffer, improve the axle location etc, but on the other i'm worried that it will start limiting the rotational movement, and stop the axle doing its job?

Any ideas?

 

[Geeman]

How are polyurethane bushes usually manufactured? I'm thinking that they are usually solid, but with a metal tube/collar to allow the movement...

 

[aragorn]

Ye, you cant bond polyurethane to metal, so when you fit a polybush in a location like this, while the bush is rock hard, any rotational force applied by the axle will either cause the entire bush to spin in the housing, or cause the pin thru the middle to spin around the bush.

The rubber bushes however are bonded to the metal housing. So when the axle moves, its actually twisting the rubber bush to allow that movement.

I'm aware that the improved stiffness from a polybush is desirable, as it helps stop the axle moving around and altering the rear ends suspension geometry, but i'm not to sure if polyurethane filling a rubber bush will end up restricting the movement too much in the direction that it NEEDS to move, and either mess up the handling, or massively reduce the life of the rubber bush.

 

[Geeman]

I think you've already answered your own question then! :icon_thumright:

 

[Matt82]

on the golfs the front engine mounts are often a lump of rubber with holes drilled into it

we fill those with no more nails

works a treat

I've just got myself two new rear axle bushes for the A4, as the old ones are "slightly" worn...

I've noticed they have huge voids in the back of them, hence wondering about polyurethane filling the voids.

I've filled mounts before, but usually ones that are supporting engines and suchlike, whereas these bushes are being subject to constant twisting forces around its axis as the axle moves up and down

Just wondering if anyone else has poly-filled a bush thats being used in this type of location before?

On one hand it seems that it would make it stiffer, improve the axle location etc, but on the other i'm worried that it will start limiting the rotational movement, and stop the axle doing its job?

Any ideas?

 

[jcb]

not sure which bushes you mean but if it rotates like an ARB bush poly is not a good idea. but you are filling an OEM rubber which would be a better option in that scenario IMO.
no amount of polyurethane is going to stop 2 ton of car moving your suspension components in ways they are NOT meant to go.
I think it transforms the handling but it depends if you want butter smooth granny taxi or an understated road racer.....
mine ain't no granny taxi anymore!

 

[aragorn]

Its the bushes on the torsion beam, similar to the ones on the rear of a golf or whatever.

On an ARB the bush sits round the bar, the bar is always free to move, but these are the main location between the axle and the car. The outer is pressed into the axle and the inner is bolted to the chassis. Just like a front wishbone bush really.

The point is that for the axle to move up and down, it has to twist the rubber, and filling it might mean it cant twist properly. Its a different scenario to a polybush, because with a polybush the inner is always free to turn.

I think that while it might be nice, i'd probably be better off leaving it, and just putting the new bushes in as is.