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"The word" from Polybush UK
MK7 - 26/6/03 at 01:42 PM

Hi,

I know this subject has been covered in the past but I've been unable to get all the information I needed and so I suspect others might too.

I spoke with a very helpful Polybush UK techie today to get some answers to my questions, here's what I found out...

These questions relate to the 2 part poly urethane (PU) 'top hat' type of bush that are supplied by companies such as MK.

1. Do not use grease on any surface of the bush. Use soapy water to assist inserting the bushes into the outer tube.

2. Do not use grease on the outside of the inner tube, use soapy water.

3. Do use grease on the inside of the inner tube to minimise the chances of the bolt rusting to the tube.

4. The tighter the fit then the better the performance of the bush. The bush is designed to distort as the suspension moves. It is not supposed to act as a bearing. If you've used grease don't worry, while this may marginally increase wear it will not damage the bush material.

5. The function of the bush is to distort as it takes up any relative movement between the wishbone and the bracket. Hence the need for a tight fit. The surfaces of the bush (inner and outer) should remain static relative to the inner and outer tubes, the relative movement between the inner and outer tubes is accommodated by the distortion of the bush. This may sound cruel but it's what the bush is designed for!!!

6. The bolt should be tighted to such an extent that the inner tube does not move relative to the bracket. Movement at this point would be metal to metal and therefore not a good thing.

7. This point is my own inference...

From what I've heard from Polybush, the bushes should only be tightened when the suspension is loaded with its normal weight. This will ensure that the inner tube gets fixed relative to the bracket without any distortion applied to the bush and so the bush will be able to distort equally as the suspension arm moves up and down.

I invited the polybush techie (Ian) to visit the site and give us his 2 cents worth.

I hope this helps you as much as it has helped me.

Russell

stephen_gusterson - 26/6/03 at 05:46 PM

this about backs up the previous discussions on here, and is basically what Rorty

sorry

Rortie

said.

atb

steve

paulbeyer - 26/6/03 at 10:44 PM

I thought Rorty recommended using Mollies Bendy Bum grease on the inner metal tube (on the mating face between metal and plastic).

Rorty - 27/6/03 at 01:59 AM

paulbeyer:

quote:

I thought Rorty recommended using Mollies Bendy Bum grease on the inner metal tube (on the mating face between metal and plastic).
Yes, that is what I said, though my choice of words differed a little!
The three different suppliers of PU bushes here in Aus, advocate the use of moly grease for the crush tube to PU bush surfaces, in fact, they go so far as to actually supply a little sachet of moly grease with each set of PU bushes for that very purpose!
Further more, at least one of the manufacturers also say NOT to use any form of detergent as an assembly lubricant, as they all contain salts, which encourages rust!
Before I moved to Aus, I used to use the red PU bushes in the UK (I can't remember the manufacturer's name), and though they didn't supply moly grease with their bush kits, they did recommend the use of Castrol moly grease.
MK7, I don't doubt for a minute that Polybush UK gave you all that info, but they are flying in the face of common opinion and practice!



OK, I've just had a look at UK site SuperFlex, and here's what they say about friction:


"FRICTION
Unlike rubber bushes, SuperFlex polyurethane bushes are designed to function rather like a bearing. This allows the suspension to move more freely around its pivotal point and eliminates the restriction imposed by the torsion pivoting inherent in most rubber bushes."


They also offer this fitting advice:

"Remove all dust, previous bush residue, paint or old grease from contact surfaces, prior to fitment.

Ensure any original outer shell is not inadvertently left in place. A common mistake where the old rubber bush has unbonded from its shell. In some instances the outer shell is intentionally left in place, as described in models and descriptions on our price lists.

Do not fit new bushes to worn, rusty, or distorted fittings. Worn components must be replaced.

Lightly coat bush contact surfaces with assembly lubricant (where supplied) prior to fitment.

Insert the stainless steel tubes (where applicable) after the bushes are installed into their housing.

Immersing high-interference fit bushes in boiling water, can assist fitting in a very cold climate.

Before the final tightening, suspension arms must be at normal ride height.

When replacing original componentry, ensure that all nuts and bolts are tightened to original manufacturer
specifications.

Bushes must not come into contact with alcohol-based solvents such as MEK, methanol, or methylated spirit.



I really don't understand why Polybush adopt such an unusual approach.

Moral: <broad Irish accent> "Sure half the lies you hear aren't true anyway!"

[Edited on 27/6/03 by Rorty]

MK7 - 27/6/03 at 09:43 AM

Hmmmm,

When questioned about soapy water Polybush said they recommended this because, over time, it would just dissapear. Perhaps the insertion lubricant that Rorty mentions is a similar, water based product (like KY Jelly???).

It seems like the different manufacturers have different religuous views about whether the bush should act as a bearing or not. Polybush did comment that some users do grease their bushes (this is starting to sound smutty) in cases where there is likely to be a large rotational displacement such as off road vehicles which have significant suspension travel but later came back to the point that the bearing effect will increase wear.

Anyway, in my case the subject suddenly became academic cos I fitted them without grease (apart from the front offside which I'd already fitted using LM grease).

Time will tell.

Russell

craig1410 - 27/6/03 at 12:20 PM

Hi,
I'm no expert but I agree with Rorty here. There is now way that the PU bushes that I've seen are designed to distort. I say this because the walls of the tophat are so thin that any significant distortion would cause them to tear. Think of rubber bushes - they have walls which are much thicker than the PU bushes and this allows them to distort in rotation. PU bushes (for Locost suspension anyway) have very thin walls (between inner and outer tubes) and can't possibly be designed to distort.

I would also agree that washing up liquid is not ideal due to the salt content and something like WD40, Grease or Car polish would be better provided they don't react with the PU. Brake fluid was always best for rubber since it didn't harm it like WD40 can but I don't know the chemistry of PU so I don't know what would and wouldn't react with it. I think it is resilient to most things though.

I'm using Nylon bushes (not my first choice to be honest) and I have used a very small amount of copper grease to assist with the fitment of the tophats into the wishbone tubes. I have done this mainly to stop corrosion in actual fact and it is fine as long as the bush still has sufficient grip not to slip during normal suspension movement. I think I need to use some sort of Nylon lubricant between my crush tubes and the bushes, anyone know what is suitable?

Just my 2p worth!
Cheers,
Craig.

timf - 27/6/03 at 12:39 PM

i assembled a set of pu bushes without any grease on the cobra replica i built and the first time i drove it the suspension squeaked like f**k so i pulled it all apart and greased the outside of the crush tube.

It stopped squeaking.

no harm was done to the bushes by greasing them same set on the car after 5 years.

Rorty - 28/6/03 at 02:18 AM

MK7:

quote:

Polybush did comment that some users do grease their bushes (this is starting to sound smutty) in cases where there is likely to be a large rotational displacement such as off road vehicles which have significant suspension travel but later came back to the point that the bearing effect will increase wear.
Actually, every thing wears if it moves, though the amount of wear in a PU bush would be impercievable in your car's life time, unlike rubber bushes.


Craig1410:
quote:

I'm using Nylon bushes....I think I need to use some sort of Nylon lubricant between my crush tubes and the bushes, anyone know what is suitable?


Moly grease will do the job admirably with Nylon too.
Incidently, Nylon can absorb water, increasing its dimensions by up to 10%! Freaky eh? So if you take your car through a ford or car wash, and the suspension tightens up, you'll know why. (Not really likely!)