Poly bushes

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Originally Posted by rick130

urethane bush + pivoting/rotating joint + lack of grease (eventually gets washed out ) = squeak big time

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With any bush material the idea is that rotation is accommodated by flexing of the material.

With the rubber bushes this is ensured (in theory at least) by the rubber being vulcanised to the steel sleeves, with the outer sleeve pressed in and the inner sleeve clamped. Problems arise if the sleeve is not secure. This is rare for the outer sleeve, not uncommon for the inner. Another potential problem is clamping the inner sleeve with the suspension not in its normal position. Any of these problems will cause rapid failure of the bush, either by breaking the bond to the sleeve or by wearing through the inner sleeve.

With polyurethane bushes, the clamping is applied direct to the polyurethane bush and expands the bush normal to that direction to give sufficient pressure on both the bolt and the hole in the suspension component to prevent movement between the metal components and the bush. Movement will take place if the clamping is inadequate due to poor installation, earlier wear on the metal bits, or deterioration of the polyurethane.

As with the rubber bushes, if this movement occurs, it will cause problems. The first thing noticed will be noise, but movement will cause wear on the metal surfaces, which is not a good idea, as while the bolt is easily replaced, the bit on the outside, and the cheek pieces doing the clamping are not that easy or cheap to replace. This wear will continue for a long time before the bush actually deteriorates to the extent that free play is present and handling deteriorates. In this sense the poly bushes are more durable.

John

Fine in theory John, in practice a poly bush rotates on it's crush sleeves. It's for this reason that some manufacturers turn helix's on the poly surface where it rotates to retain grease, and on some bushes, eg. shackle bushes, they use hollow pins, grease nipples and a turned bush inner surface to accommodate regular greasing. ARB use this system, as do TJM and Super Pro.

Quote:

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Originally Posted by rick130

Fine in theory John, in practice a poly bush rotates on it's crush sleeves. It's for this reason that some manufacturers turn helix's on the poly surface where it rotates to retain grease, and on some bushes, eg. shackle bushes, they use hollow pins, grease nipples and a turned bush inner surface to accommodate regular greasing. ARB use this system, as do TJM and Super Pro.

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Yes, and this highlights the major problem with polybushes! The elastomeric bushes were invented about seventy years ago to get away from chassis bearings that needed regular greasing (which they didn't get) and which used the surfaces of the major suspension components as bearing surfaces, resulting in expensive repairs when worn, which was often. By going back to bearings that need regular greasing you are going back seventy years. The only advance is that the parts that wear are replaceable - provided that the bush rotates on the crush sleeve as intended.

John

yes, and the major reason why I don't like urethane in a rotating bush.
I reckon they are great in compression.

The only place I have poly bushes that sees any rotation is the panhard rod. The rotation isn't great.

I've had poly's in there for about 2 years and a year ago took one of the crush sleeves out. I can tell you they don't come willingly. It was tight enough for me believe there's no rotation there, it's taken up in flex inside the bush.

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Originally Posted by Dougal

The only place I have poly bushes that sees any rotation is the panhard rod. ......

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There is more rotation than on the panhard rod on:-

1. Front bushes of the A-frame
2. Rear bushes on the rear lower link.
3. All bushes on leaf springs.

Certainly the other bushes have less rotation, and there is less objection to the use of polyurethane bushes in these locations - the main objections will relate to the vexed question of whether you want to modify the original suspension characteristics or not.

John

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Originally Posted by JDNSW

There is more rotation than on the panhard rod on:-

1. Front bushes of the A-frame
2. Rear bushes on the rear lower link.
3. All bushes on leaf springs.

Certainly the other bushes have less rotation, and there is less objection to the use of polyurethane bushes in these locations - the main objections will relate to the vexed question of whether you want to modify the original suspension characteristics or not.

John

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Funnily enough, there are two reasons I run poly bushes in my front radius arms. The first is longevity, metalastic ones kept chewing out in short order. The second is the needed extra roll stiffness in the front.
My vehicle is tailhappy enough to be fun with poly bushes in the radius arms, was tailhappy enough to be scary without.

12 months ago I replaced rubber bushes throughout my RRC with Noltec (blue) offerings. I had used poly bushes on another rangie and found the change from rubber to poly was quite noticable, particularly more noise and less articulation, but they lasted forever!
I have found the Noltec bushes as good if not better than the rubber, certainly easier to fit, and the before and after ramp tests etc showed similar results, given the rubber were well all worn, I was happy with that. I have since supplied a couple of local 4x4 owners with Noltec stuff. One was replacing SuperPro and the other original rubber. Reports have been positive, in that they have kept replacing other bushes etc. In the beginning Noltec was sold to me as being same softness etc as rubber, and from my experience I would agree with their claim.