Disco I Trailing Arm Bushes

I'm confused!

Are these the bushes at the rear(axle) end of the radius arms that we're talking about? From your description about the positioning of the axle it sounds as though it's the front (chassis) end with the triangular mounting plate.

Are these standard design i.e. Land Rover-pattern bushes or split polyurethane ones?

I don't understand "crush the tube" - I've a suspicion that you may not have the parts assembled correctly. The big nut at the front end should be tight but nothing should crush as in 'collapse'.

In order to reposition the axle so far as to affect the driveline doughnut, something's horribly wrong!

Hi Dougal

Thanks for your reply - I've taken a couple of photos which should make things clear -

Hi Dougal

Thanks for your reply - I've taken a couple of photos which should make things clear -

They look fine to me.

Mike

That looks perfectly normal!

Are those the plastic bushes? - you say 'rubber', is that what you meant? Is it the one-piece Land Rover style with the rubber bonded to the triangular plate and the inner tube or the aftermarket multi-piece design?

The one-piece design just clamps up the central tube between the thick washers: the rubber may not fully touch the washers. That's normal.

If it's the multi-piece design there may be an issue with compressing the plastic so that the central tube is properly clamped by the two thick washers. You should be able to determine by feel whether the clamping has been achieved or not: the inner tube will not collapse. If you feel that it's not clamping could you have been sold an inner tube that's too short? It doesn't look seriously wrong to me.

Could you explain what you mean by "bring everything into line as it was before"?

The longitudinal positioning looks just fine, the parts are fitted in the correct side of the chassis mount so there's no reason for the axle position to be compromised.

Which gets us back to the beginning - what's the reason for starting this conversation? Is it the problems with the rubber doughnut?

Does the sliding part of the propshaft slide? Is it the correct length of propshaft? If the shaft is either too short or too long the doughnut could be strained: similarly if the shaft cannot change length as the axle moves up and down. The shaft's not bent is it? Is the centralising spigot that locates in the diff input yoke and goes through the centre of the doughnut present and correct?

The bushes are rubber one piece LR style. There is a metal tube inside the bush which will not compress hence the rubber part of the bush is doing nothing and would make no difference if it was not there. On the old bushes I took off, the tube was soft enough to have been crushed/ flared at the ends allowing the rubber element to be compressed =96 so much so that they were difficult to remove through the holes in the chassis mountings as their diameter was greater than that of the holes through which they had to pass. The MOT inspector had failed these because they had cracks in them.

Because the new bushes will not squash down, the trailing arms are holding the rear axle backwards further than before and given that the axle is held by mountings above , the net effect is to rotate the axle causing the centre line of the drive to the axle to be below horizontal / not in line with the drive train. This means the doughnut is constantly being flexed as it turns hence its failure. Cracking of the doughnut being the observed symptom.

I can sketch something up if necessary.

Regards, Tony

Tony, I don't think that you understand how this is bush working.

The rubber IS doing almost everything! The longitudinal forces from the radius arm are transmitted from the radius arm to the bush central tube thence into the rubber. The central tube is bonded to the rubber. The rubber then transmits the forces into the triangular plate and hence into the chassis. The large washers do little more than prevent the rubber being over-stressed by limiting the longitudinal movement. The washers also act as a safety stop in the event that the rubber bonding fails or the rubber 'disappears' as their OD is greater than that of the central hole in the triangular plate.

As I mentioned before, I don't think that you've got anything wrong with the bush installation. It looks just fine.

Those bushes were well beyond their sell-by date. The central tube should not be collapsing.

I can understand what you are trying to suggest but think that you're mistaken. Firstly the amount of displacement at the bush will be about

Doughnuts do crack with age and use. Unless you've gone through several in short succession, you may not have a problem. If you do have a doughnut issue I'd suggest that you look in the driveline for a cause along the lines I suggested before. I'm assuming that the MOT would have revealed any other suspension bush issues serious enough to cause doughnut problems.

Happy hunting!

Tony Hi,

is your Disco lifted?

Take care Pantelis Giamarellos

Dougal's right.

I'd suggest that you've had an issue with the previous trailing arms, but didn't know it, so when you replaced the bushes you're trying to make them fit what was already wrong, IYSWIM!!!

Whereabouts are you in the country, someone might take a look, certainly I would if you're anywhere near Doncaster.

The doughnut on my 300 Tdi Disco has gone twice in 125k miles, but is going to be replaced by a 'proper' UJ assembly shortly as it's ready for a new one already ..

I have replaced this type of bush many times and have never seen or heard of an inner tube that crushes in any way,

Mike