Black Polybush issues?

[mgcjag]

Hi All....im refering only to the black PU wishbone bushes manufactured by Polybush......Iv been notified that there have been problems with newly fitted bushes failing/breaking up after not to many miles......the people iv been talking to have been useing these bushes in their restorations for quite some time being the best option available considering the unavailability of original bushes........its only recently thay newly fitted bushes have failed....so whats happened...are the "new" Polybushes somehow different.......have you had problems.....i have flaged this to one of the usual supplier's who is going to investigate............iv heard nothing on this forum or JagLovers about failures........your help appreciated if youve had a problem please let us know.....Thanks....Steve

[phoenix]

While you are talking about poly bushes I have always thought that unless you are going to race your car etc they are a bit of a waste of time. Speaking from experience in using in race and rally cars they give a more positive feel yes but as in most things there is a trade off and that is a rather harsh ride.
On a road car I would always try to remain stock.

[mgcjag]

Hi Brian there are many different PU compounds with different hardness ratings and different ways to fit them...thats why i refered to the Black pu bushes made by Polybush.......used by many restoration companies as a direct replacement for the original rubber that is no longer available. .....they were of similar hardness and fitted under compression in the same way as the original style......these were definatly not a race option.....Steve

[mgcjag]

Just to add.....if you have fitted these bushes then please have a visual inspection.....can you see any torn ends of the PU.....on at lease one occasion iv been told that the bush break up allowed the wishbone to move forwards and rub on the bush retaining spacer /washer......so please check.....especially if you have fitted them recently....one case iv heard they failed in less than 100 miles use......Steve

[mgcjag]

Just bumping this up......would like your replies please.....have you fitted black bushes by Polybush....have you had any problems.........have you or can you look and check yours.....are they looking ok or breaking up.....please let us know.......This is not a personal issue just for me...im trying to collect info for the forum....thanks...Steve

[bitsobrits]

I have the black Polybush 'street' bushings, about 15 years/15k miles. They were just fine until this past year when I had the suspension settings changed, and the shop that did the work rather 'chewed up' the ends of the bushings on the upper arms when changing up the caster settings. So I would say they require a bit of care when working around the suspension.

[lowact]

I bought this kit a long time ago, from Jaguarspares in UK. When trying to fit the wishbone bushes, so many issues that I basically junked them, bought a SuperPro kit instead. All I used from this Polybush kit were the roll bar bushes. I could write a book about what is wrong with these wishbone bushes, imo by design they must fail.
In the pic are the bushes for one side, on the left is the pair of bushes for an upper wishbone, on the right are bushes for a lower wishbone. Also shown is four of the eight “retaining washers” provided.

[mgcjag]

Almost 400 views but only one reply from a member thats has these bushes fitted....anyone else have them fitted.....Steve

[malcolm]

Hi Steve, I have polybushes, but don't know if they are "black" polybush. Mine were on the car when I got it, 9 years and 45,000 miles ago. No problems.

[Fuel.inj]

Hi Steve,
Similar to Malcolm’s response. I have poly bushes fitted as and when I purchased the car but unknown manufacturer. I’ve checked them and they are fine. ATB.

[mgcjag]

Thanks guys......more replies please......it all adds to our understanding .....Steve

[neal herridge]

Hi Steve.
I am having problems with these Polybushes & I know of other people who are getting problems.
The flanges peal off at the ends & yes I do set them up with all the weight on the car. The last set I fitted gave problems after about 500 miles .
I have fitted them for years without a problem until about one to two years ago when the problem started.
The polybushes & the original bushes are designed to work in sheer looking at the workshop manual will confirm this.
I have started fitting Superflex bushes which work in a different way, they are meant to rotate about a st/steel center but they are giving problems as they are rotating in the housings but that's for a other time.

Neal.

[mgcjag]

Hi Neal....do you have failed bushes.....have you been in contact with your supplier...im dealing with SNG who are getting a case together to approach Polybush.......will PM you for more details.....Steve

[lowact]

I have started fitting Superflex bushes which work in a different way, they are meant to rotate about a st/steel center but they are giving problems as they are rotating in the housings but that's for a other time.

Hello Neal, rotating bushes, same as sheared flanges, is due to excess torque being applied by the adjacent (rotating) washers. This is supposed to be prevented by the length of the bushes inner tube, which must be slightly longer than the installed length of the bush, so that the washers are tightened onto the ends of these steel inner tube and do not press unduly onto the flanges of the bushes.

These issues can occur even without the washers. The front lower wishbone arm has a sculptured indentation opposite the bush, without the washer the flange of the bush expands into this indentation such that the flange is effectively keyed to the wishbone causing the bush to rotate (or the flange to shear off) even faster than by a washer dragging on it. Imo whenever there are suspension bush issues, if any of the washers are missing, there is 90% of the problem.

Here is a photo showing the “sculptured indentation”. Note this is with the same type of bush as you, rotating type not flexing type:

[mgcjag]

Hi Colin......I raised this issue of the black "Polybush" bushes breaking up or the ends shearing off becaus it is something that has only recently started to happen....and been identifeid by a few very well known restoration companies who are very experianced in working on E types. .....so we arnt talking about someone fitting these incorrectly......were working on the assumption that the actual PU compound or something in the manufacturing process has changed..........some of these companies have been installing these bushes for many years with no problems.....but recent failures have been noticed on newly installed bushes after not many miles..a few hundred or less.....Steve

[AussieEtype]

I think the issues you raise with "black" polybushes also apply to most other polybushes.

In 1999 I fitted purple Nolathane poly bushes to my Series 3 - these bushes are Australian made and have a decent reputation. My car has not been on the road for nearly 30 years and other than one or two drives around the block in that time the car has just sat on its wheels.

The car is currently in for work to recommission it and when preparing the car I jacked it up and for the first time in many many years the suspension was dropped to full extension and any exposed polybushes just crumbled and fell apart with no help other than the suspension dropping. Looking at the pieces they had totally "dried out", ie they had hardened and crumbled. Not sure what the bushes are like inside the suspension components but I assume the same - not good.

Based on this experience, a discussion will need to be had on what to replace them with. My thoughts are the original rubber units but these also fail (perish) but are a known quantity.

Garry

[mgcjag]

My thoughts are the original rubber units but these also fail (perish) but are a known quantity.

Originals...yes....but whats on offer now from the usual suppliers arnt "original" they are after market reproduction...yes it is possible to find some suppliers with "new" "rubber" bushes stamped Metalastik....but is the compound used the same as original?........This is why some went for black manufactured by "Polybush"....note that not all black PU bushes are the same.....different manufacturers have different hardness ratings and different ways that they operate in the houseing/wishbone........Steve

[lowact]

Steve, imo Polybush type 31C (lower wishbone) cannot be installed correctly by design. Early failure is inevitable.

I bought a set ~7 years ago, didn’t use them due to the obvious flaws. The material is very soft, like silicone. It tears relatively easily, like silicone. Softer than rubber, weaker than rubber, unable to flex like rubber, straight away not as good as the oem bushes.

The length of these bushes (excluding washers) is dictated by the dimensions of the wishbones and frame. Must be 47 mm and this is exactly what the length of the bushes inner steel tubes are, i.e. these bushes are “correctly” installed when the oem washers are tightened up hard against the ends of the inner steel tube (duh).

For this type of bush the inner steel bush is supposed to be the longest part of the bush. For Polybush type 31C (lower wishbone, all e-types) this is inexplicably not the case, the resilient part is more than 50 mm long uninstalled. When it is pressed into the housing the diameter is reduced causing elongation to more than 53 mm, i.e these already-strained-to-the max bushes must then be compressed 6 mm each, just to install the wishbone. Procedure is to assemble the wishbone including the bush housings (with the shock absorber mounting bolt loosened as required) and tighten the fulcrum shaft castellated nuts until the holes in the bush mounts line up with the holes in the frame. If you are precious about your car this is very hard to do, the amount of load you have to apply is tremendous, just to accommodate a bit of plastic that shouldn’t be there… If you are not a “Reputable Restorer” you might start to imagine that the wishbone washers (C15376) are not compatible with your aftermarket bushes, they should be left out, installation is then a lot less stressful? This thinking is supported by the fact that only one end of the 31C bush is designed as a bearing surface, the other end has embossed markings on it. Such thinking is utterly wrong; C15376s cannot be safely left out.

What you end up with, if the washers were retained, is the flanges of the bushes clamped extremely hard between the stationary bush housing and the rotating washers, so they will shear off. If you left out the washers, the flanges of the bushes are clamped to the stationary bush and keyed into the rotating wishbone “sculptured indentation”, so still they will shear off. Disappointing to hear that “reputable restorers” are not competent enough to realise not to install these into customer’s cars. And SNGB advertising them as “uprated” is just sad.

Garry, imo you are correct, for S3 at least, there is nothing available that is a patch on the oem bushes. S1/2 would do well to adopt these bushes.

For explanation, there are effectively 1st and 2nd generation polyurethane (PU) bushes. 2nd gen corrected the shortcomings that caused the 1st gen issues that you describe but introduced others.

1st generation PU bushes mimicked the rubber bushes they were marketed to replace, size and construction: There are no sliding surfaces, rotation (suspension travel) is by the rubber flexing, enabling the inner steel tube (which is bonded to the rubber) to rotate relative to the outer diameter (incl. flange) of the bush, which is held by the bush housing. Axial movement is by the rubber stretching, note all this requires the length of the inner steel tubes to be longer than the length between the flanges.

Fundamental issue with the 1st gen PU bushes was because PU cannot flex to the same extent as the rubber. Being “aftermarket” there is no opportunity to increase the size of the bush to compensate, the PU would tear, the bush would rotate in its housing or the fulcrum shaft would rotate within the bush.

With 2nd generation PU bushes the inner steel tubes are not bonded to the polyurethane, instead are free to rotate within the polyurethane, the above failure modes are eliminated. Axial shock absorption is not as good. With rubber bushes, because the rubber is bonded to the steel inner tube the rubber would stretch to absorb wheel impacts. With 2nd gen. PU bushes this stretching is not possible, instead the bushes have large flanges that bear onto thrust washers, you feel every shock.

[mgcjag]

Hi Colin.....i understand all that you are saying......was your experiance just based on the one set of 31c bushes? I notice that you didnt actually use them...so you didnt have them break up in use.....you mention your bush mounting blocks on the assembled wishbone not lining up to fit in the frame...and you mention washers C15376....im assuming that you only had the one fitted and not 2 as incorrectly shown in the parts diagrams......
I have fitted quite a few sets of these and know others who have and not had the problems that you experianced...so i would not say that the 31c would inevitable fail due to its design.....could it be that there was just a problem with the set you had?.......so far we have no other members reporting failures.......but the main issue i started this thread about is with what looks like a faulty batch.......around 6-9 months ago.........and reported by some restorers.....who had no previous problems with these bushes......Steve

[Geoff Allam]

Has there been any resolution of the black polybush failure issue? I purchased a set about 2 months ago from SNG and am wondering if I should be nervous about installing them.