Poly Bushes, are they all the same grade?

[don58van]

Still waiting to hear where they are NOT suitable......

I am not an expert on the subject, I am guided by others who I think might know more about it than I do.

Here is an example from this forum, although there are several similar statements by the same author:

On the tie-rod - best to only fit ONE poly bush each side - on the outside, with a rubber bush on the inside to preserve some flexibility.

Sun Jun 09, 2013 9:03 pm

This would suggest to me that this contributor, who is well regarded on this site, believes that the inner tie-rod bush should be rubber, not poly.

The article in Minor Matters by Howard Bentham puts the view that both the inner and outer bushes should be rubber, not poly.

An issue that interests me, is that there is still a lot of debate about whether the poly bushes need to be greased or not. Some of this discussion is concerned with suppressing the tendency for poly bushes to squeak or creak. However, in positions where there is rotation around the axis of the bush, it seems to me that this may affect the way the bushes function. Any comments?

Cheers
Don

[IslipMinor]

Tie rod front bushes - with a lowered car, the tie bar is much better aligned with the front mounting bracket, and we have had poly bushes on both sides of the bracket since the restoration was completed 15 years and almost 50,000 miles ago - still good as new. So now we have three suggestions - rubber/rubber, poly/rubber, poly/poly. Just need the rubber in front and poly behind to complete the set! I wonder if anyone has done that??

Lubrication - when I fitted them originally, the recommendation from Superflex was for no lubrication and we did get a little creaking from the front somewhere at low speeds, such as over speed bumps. When I fitted the new negative camber eye bolts a little while ago, I also replaced the eye bolt bushes with new 'red' ones (the old purple Superflex were still perfectly OK, but given the opportunity it seemed a good idea) and applied a smear of copper grease - no creaks!! Was it the grease or are the current bushes more 'self-lubricating'?

[Matt]

Still waiting to hear where they are NOT suitable......

I am not an expert on the subject, I am guided by others who I think might know more about it than I do.

Here is an example from this forum, although there are several similar statements by the same author:

On the tie-rod - best to only fit ONE poly bush each side - on the outside, with a rubber bush on the inside to preserve some flexibility.

Sun Jun 09, 2013 9:03 pm

This would suggest to me that this contributor, who is well regarded on this site, believes that the inner tie-rod bush should be rubber, not poly.

Im not sure that is the case with the minor tie bar, as the front wheels only provide a breaking force, so the bush on the rear only really does anything when you are in reverse.

The mini, however, which the poster in question also knows about, is a different kettle of fish, and that is recommended to give a bit of flex to make taking up the power a little less harsh and to help prevent skipping on rough surfaces.

[MarkyB]

Some of the poly bushes I've got feel like they have been machined out of nylon, no give at all, too far from what was fitted originally for my taste.
Comfort grade sounds fine given the quality of rubber parts these days.

[bmcecosse]

I found on the Minor that it was extremely difficult to get the outer nut on with two poly bushes - and then when tightened up (with some considerable difficulty) the tie rod was virtually rigid and very unyielding. It seemed to me it would be likely in time to cause damage to the front mount - which as standard is not all that strong. So - since braking is the main consideration I used a new (old stock though !, not current cr@p) rubber bush on the inside and poly on the outside. This is still 'firm' but movement is possible. On the Mini - same idea (but front mount strengthened with gusset welded in) but here the power also has to be resisted - and I used poly bushes both sides of the mount - the inner bush thinned down slightly. The vertical suspension movement on a Mini is also much less than on a Minor! So the required radial movement of the tie-rod is also much less. The tie rods on my Mini were 'adjustable' for length - so caster angle was independently adjustable anyway. So - to get back to the question (which I have answered myself) - this is the only place I know where a poly bush could be unsuitable - I was waiting to see if anyone came up with it!

[don58van]

Im not sure that is the case with the minor tie bar, as the front wheels only provide a breaking force, so the bush on the rear only really does anything when you are in reverse.

The (potential) problem with poly bushes on both sides for the tie-bar is not when the suspension is at or near its resting height when braking or accelerating, but when the suspension is in bump or droop.

Then again, under harsh acceleration (from its mighty 803, 948 or 1098 engine) or severe braking (from its powerful 7" or 8" drums), the front suspension could go into droop or bump under acceleration or braking respectively.

The point I am making here is that it is the up-down movement of the tie-bar, not the fore-aft movement that is the issue.

Don

[LobbyLudd]

[quote="IslipMinor"]Just had a reply from 'Polybush' to say that their blue 'Comfort' bushes are 65 Shore A and the red 'Performance' bushes are 85 Shore A. They also said that the Comfort bushes are similar in ride quality to the original rubber bushes.


The company 'Polybush' were good enough to clarify this info to 'Islip' in providing the Shore grades of their own supplied products , it was also interesting to see that their Blue '65 Shore A' in their opinion should 'replicate' what they say is a 'similar' ride quality to the original rubber type. (That really was the thing that drew my attention!)

Would it be now be of interest to establish a realistic comparison of a typical 'Shore' grade that an original 'top quality' type rubber bush would be (given the possibility obtaining a similar quality today) for direct comparison in hardness/elasticity ??

(Or am I assuming this to be far too simplistic to make this type of comparison, given any other specific or differing material characteristics of Rubber v Poly)

[bmcecosse]

You are over thinking this - just fit the 'comfort' grade - and enjoy.......

[don58van]

Wouldn't it be great if we could do simple, non-destructive hardness tests ourselves, so that we could check these rubber and poly components before buying them or fitting them to our cars.

This is what we need:
http://www.youtube.com/watch?v=_QwFPfUq3I8

But seriously, I would appreciate a simple, cheap way to get reasonably accurate and consistent measurements of hardness of these components before they are fitted. Any ideas?

Why? Here is an example: There is a popular brand of poly bushes made here in Australia. I don't know how they compare for hardness to the other brands being discussed here. Further, even when manufacturers give shore ratings for their products, we don't know how much tolerance they have in their manufacturing process.

There may be people out there who have all the relevant knowledge about flexible bushes for the Minor (one Minor specialist is often mentioned here and elsewhere). I say that in view of the unavailability of serviceable rubber bushes we need to have this information in the public domain.

Cheers
Don

[Declan_Burns]

My home made bushes are still fine after a couple of years.
Regards
Declan[frame][/frame][frame][/frame]

[bmcecosse]

Excellent! But where can we get the liquid 'poly' to make our own Declan??

[Declan_Burns]

Roy,
Here's a link to it.
http://www.weicon.de/pages/en/products/ ... ethane.php
I bought it on ebay but I don't see it on the UK ebay.
Here it is on our ebay in various grades: 80, 60 and 45.
http://www.ebay.de/sch/i.html?_odkw=wei ... n&_sacat=0


Here's the Distributor in the UK:
http://www.weicon.de/pages/en/contact/p ... .php?co=UK

Here's the mould I made to make them. The urethane is easy to work with and doesn't stink but as with anything a bit of practice is involved. There's enough in a tin to make about 50.


Regards
Declan[frame][/frame][frame][/frame]

[bmcecosse]

Excellent!! Thanks Declan! I just need to think about moulds now.....

[Declan_Burns]

Roy,
I use PVC as it's easy to turn down on the lathe. Cheap on ebay. If you have no Access to a lathe you can use tubes or plastic rings or bottles or the like.
Regards
Declan

[IslipMinor]

Update on the Shore hardness - I emailed SuperPro in Australia today and am waiting for the their reply.

Polybush are the only supplier so far that seems to have good information about what they are selling. The colours are what the supplier uses.
[frame][/frame]
Are there any other suppliers that should be included?

[LobbyLudd]

1. SuperPro Europe (in Somerset) ?

2. Bull Motif ?

[bmcecosse]

I would have thought Bully as the major supplier of Minor parts - and perhaps DSN (if they do poly parts - haven't looked) and MOSS (ditto - re poly parts).

[don58van]

Nice work Richard!
Thanks for your efforts.

Declan -- Thanks for sharing.

Cheers
Don

[IslipMinor]

Have emailed Bull Motif and SuperPro in the UK as well.

[LobbyLudd]

You are over thinking this - just fit the 'comfort' grade - and enjoy.......

Just thought for one tiny moment you were beginning to ever so slightly lose interest in this one


Are all these 'poor quality' rubber bushes that are constantly reported being now sold from the far east?
Is there not a maker that still makes a good quality comparable type that we could get a useful comparison in with hardness with the ranges of 'Poly' type bushes was obviously my point. (Perhaps it would be of great interest to then eventually include a typical 'rubber grade 'A pattern tip instrument test shore grade figure' within Richards excellent work with his 'table of suspension bush grades available) I just thought that would eventually give us a more complete picture with a full spectrum comparisons on this subject Rubber v Poly

(Hope the one well respected supplier were thanked for providing the outstanding info so far that 'Poly bushes are harder than rubber) as a grade rating