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Clifford Pope · Apr 7th, 2023, 09:18

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?

Apr 7th, 2023, 09:18	#1
Clifford Pope Not an expert but ... Last Online: Today 08:21 Join Date: Dec 2001 Location: Boncath	Trailing Arm large bushes 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?