Rubber or polyurethane bushes

[darranlatham]

Which is better rubber or polyurethane bushes on leaf springs on traveller

[philthehill]

The fitment of Poly Bushes to Minor rear spring eyes is the way to go.
The rubber bushes even those produced by BMC/BL were not really up to the job.
Way before Poly Bushes became the norm the rubber bushes would be replaced with the one piece Metalastic bush normally fitted to the Morris J4 suspension.
This is a mod I have done for the rear spring front eye which involves the use of a Metalastic bush. The cap head bolt gets rid of the problem of holding the inner end of the original BMC pin.

Rear spring front bush.JPG (1.27 MiB) Viewed 2156 times

There are different shore 'A' harness bushes suitable for the Minor springs. Poly Bushes with a shore hardness of 70 'A' are suitable.

[jagnut66]

Modern rubber is rubbish and doesn't last.
Poly bushes all round (for everything) everytime.
For example, I initially couldn't find any rear axle saddle bushes in poly for Sally, so I bought rubber ones and fitted them.
Now bear in mind she's on axle stands being restored, not on the road under load. The rubber saddle bushes showed signs of fatigue, namely cracking and splitting, within six months.
I have since found and fitted the Poly ones below.
Best wishes,
Mike.

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[kevin s]

The only ones I would keep rubber for are the tie bar ones, going too stiff on these will introduce significand bending loads which they are not designed for.

[philthehill]

As regards the tie bar - use a rubber bush to the rear for articulation and a poly bush to the front for load bearing. Then you have the best of both worlds.

[Nourish]

what about the various colours?

[philthehill]

The various colours do not determine the Shore 'A' hardness.
The colours appear to be just random.
Below is a selection of spring eye bushes in various colours. The one on the extreme left is an original BMC soft rubber bush. The one on the extreme right is a Super Flex poly bush. The in between bushes are poly bushes of various Shore 'A' hardness and from various suppliers.
Unless you have a Shore 'A' hardness gauge or the supplier states the Shore 'A' hardness it is as much pot luck as to what Shore 'A' hardness you end up with. So far I have found that only the better quality and so more expensive bushes do quote a Shore 'A' hardness.
A Shore 'A' hardness of around 70 is about right for a non modified Minor.
Fortunately I have a genuine calibrated Shore 'A' hardness gauge (see below) so am able to determine the Shore 'A' hardness of all bushes.

poly bushes.JPG (1.24 MiB) Viewed 2049 times

Shore gauge.JPG (2.36 MiB) Viewed 2044 times

[jagnut66]

Interesting, as I was always led to believe that the green ones were pliable enough to be suitable replacements for Minor rubber bushes....
In a nutshell, you're saying the colour is completely irrelevant.
Best wishes,
Mike.

[Myrtles Man]

Some interesting comment on the subject here:-

https://www.jaguarforum.com/threads/sus ... ry.122813/

[philthehill]

Yes - the colour is irrelevant unless you have a universal grading of Shore 'A' hardness against a qualified colour.
At the moment you can have two bushes the same but of different colour with both having the same Shore 'A' hardness.
I have tried the Shore 'A' hardness meter on various spring eye bushes and this is what I have found.
BMC rubber bush.....................60 Shore
Yellow bush.............................75 Shore
Red bush.................................85 Shore
Black bush...............................75 shore
Blue bush................................90 Shore
Green bush..............................87 Shore

Note that the yellow and black bush have the same Shore at 75.

[jagnut66]

I note the green one is quite a bit higher than the original rubber spec.
I Believe this isn't a problem in most areas but people keep mentioning the tie bar bushes.
Up to now I've just been fitting the green poly replacements and I've never had an issue in 11+ years, so my question would be are all green poly bushes the same shore hardness?
Best wishes,
Mike.

[philthehill]

To answer your question - are all green bushes the same Shore hardness?
I would say no.
It would be more than helpful if suppliers stated the Shore hardness of the poly bushes they are supplying.

[don58van]

I would suggest that colour cannot be relied on as an indicator of hardness. While one or two manufacturers seem to have used colour to identify different hardness within their range of bushes, as far as I can see, for most manufacturers colour is purely a marketing decision.

I bought a cheap durometer. It is perfectly fine for making comparisons. I have some NOS mowog rubber bushes as references.

Don

[jaekl]

Since rubber bushings twist and poly bushings don't (the pin rotates), you really can't compare the rubber durometer reading with poly. A softer poly bushing allows more lateral movement if required, but is also a indication of the ability to support weight.

[don58van]

I take your point. Poly bushes do function differently in some respects than rubber ones. Nevertheless, it is still useful to know if a poly bush is softer or harder than a factory rubber one. For example, a poly bush that is much harder than a factory rubber one is unlikely to suitable for anything other than a track car (solid nylon ones were available here in Oz for track cars some years ago). A poly bush that is much softer than a factory rubber one is likely to be good for someone who is looking for a high level of isolation from suspension harshness and perhaps noise--but not ultimate handling.

So I maintain that the comparison between rubber and poly hardness provides a useful reference.

Don

[philthehill]

The most important thing to bear in mind when replacing rubber bushes is the service life of the bush.
BMC rubber bushes were notorious for having a short life. Current rubber bushes are not much better and in some cases worse.
Poly bushes give a much better service life but care must be taken when choosing the right Shore hardness against the application.
Poly bushes should be greased when fitted and lubricated on a regular basis.

[panky]

I pinched your idea Phil



I also fitted poly bushes to the lever arm damper pin, fitted grease nipples there too and lubricated with red grease.

[philthehill]

Well done.
Any chance of a photo of the top link bushes with grease nipple.
Phil

[panky]

Here you go.





I chamfered the inner edges of the bushes to allow the grease to flow around a bit more easily

[philthehill]

Thank you for the photos.