Trailing Arm large bushes

[Clifford Pope]

I've just replaced these bushes for the MOT, and used poly bushes.
It went fairly straightforwardly; drilling and burning out the old bushes was quite hard work, but the new ones pressed in easily with just a G-clamp.

But I am puzzled as to how exactly they work.
The traditional rubber ones are bonded to the inner metal tube, and also to the outer metal sleeve. The sleeve is then a very tight fit inside the fittings on the rear axle casing. So the necessary suspension movement takes place in the rubber itself, twisting and stretching as the suspension moves.

But the poly bushes are not bonded to anything, are not a very tight fit either at the sleeve or the tube, and indeed are greased on assembly to make them easy to fit. The metal tube is exactly the same length as the bushes, so the plastic bushes are not squeezed very hard between the sides of the trailing arm, the force being constrained by the metal tube, which is a tight fit inside the arm and is tightened hard by a bolt.

So it seems to me that all the movement takes place between the tube and the bush - it is simply a well-lubricated bearing. Or have I failed to understand something?

[Bob Meadows]

I can't really comment on the Polyurethane bushes as I like the original type:~
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One easy method for removing the trailing arm bushes is to cut them out with a reciprocating saw: two cuts for each at inner points near the arm- they can then be knocked out with ease.
After using two methods, puller being the other- cutting takes no time at all.

One very frustrating job that can be made easier.
Bob.

[classicswede]

The grease is not to aid fitting to to aid rotation. As you say they are in a sense a bearing but cushioned.

[Clifford Pope]

That's as maybe, but the grease inevitably also aids getting the tube in as well lubricating it in action once fitted.

I'm still puzzled, because these particular poly bushes seem to rely on a completly different principle from others I have come across. When I fitted trailing arm bushes to a Triumph 2000 a few years ago they were much more difficult to fit. There was no grease, the bushes were longer than the metal tube, and the whole assembly had to be compressed by a G-clamp as the bushes were squeezed hard between the flanges on the chassis as the arm was jacked up and forced upwards into position. It was very difficult aligning the holes to get the bolt into the second hole, and I had to make a special alignment tool by grinding a tapered point on a section of spare bolt and tapping it through using the real bolt.

A recent thread on a Series LandRover forum shows that kits for poly bushes contain specially sized penny washers with central holes to match the diameter of the metal tubes, hence squeezing the bushes very tightly when the bolt is tightened.

The principle of both these types of poly bushes seems to show that they are not "bearings", but are designed to twist and stretch just like the previous rubber bushes were.
Tempting as it would be to use some grease to aid assembly, that would have negated the function of the bushes.

[classicswede]

It is all a case of the right design bush for the application

[honestjoe]

Hi Clifford..it"s a whiile ago but i remember doing this job..I ordered poly bushes but they did not come with the outer shells so i returned them and bought the original rubber ones..I couldn"t work out how the poly ones would work without the outer shells to fit snug into the eyelets to even the load.To the best of my knowledge back then they did not supply outer casings and were intended to be used with original shells?..Did yours come with them?...BTW bertha is on her second set of bushes and third set of trailing arms..HJ.

[Clifford Pope]

Yes, the old shells were perfectly sound - I just had to drill/burn out the decaying rubber bushes, and then give a whisk with a sanding drum to clean them out.

Since then they have started sqeaking and groaning after about 100 miles of use. I'm going to check that the bolts are still tight.

[Bob 1967]

I got a mini lathe from amadeal many moons ago and have not really used it for anything since.
Polly bushes would be easy, if I had the dimensions.
I would just buy a 30 or 40mm diameter round stock.
The tip of the tool for working with Nylon and Poly plastics is ground so it drops from front to back.
I could probably clean the original inner metal bush, between centres and reuse it. That would depend entirely on its condition of course.

Had about 10 years on lathes in a previous life.
I made stainless brake pistons for a Gpz 750 on an old Colchester back in the '00s. They were complete with a nylon insert( Kawasaki were looking for £75 for one at the time)

[honestjoe]

Hi Bob..my outer shells were toast...it took thirteen hours to do the job on the farm and i would probably put the originals back in again if i live that long..I kind of know what i"m doing even if its hard..hj..I so admire your lathe work..!

[Bob 1967]

Was thinking of using a hole saw to cut the rubber section, just to separate it from the inner and outer metal.
This is not a job I need to do right now, just planning ahead.