Polybushes

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peterc
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Polybushes

Post by peterc »

I am about to have some polybushes machined to fit my shock absorber ends. Does anyone know the tolerances of the fit of this type of Bush. E.g. how much of an interference fit into the shock absorber ends?
I had obtained replacement rubber items from the supplier but they arrived with 0.5” bore not 12mm. Attempts at machining a thin sleeve were unsuccessful hence the change of tack to machining a complete new bush.
I have not located any off the shelf sleeves of the correct dimensions as they all seem to be for the wishbones etc.
Of course the alternative is to upgrade to Gerry’s latest Gaz shockers.
Peter C
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simonjrwinter
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Re: Polybushes

Post by simonjrwinter »

Speaking from personal experience (and not on the cobra frankly)
The difference between even slightly worn shocks and decent new replacements is night and day.
After replacing my only shocks on the TR6 (admittedly only lever arm dampers) with 30% uprated reconditioned jobbies of the same type, even my wife said “the car feels really smooth” within 5 minutes of being driven….
Of course if your dampers are performing as they should, re-bushing makes sense….
TR6 (V8) Hawk 289 FIA (V8) Doing my bit for global warming.
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peterc
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Re: Polybushes

Post by peterc »

Hi Simon, you are of course correct.
My shockers have only done 22k miles but I have often thought the newer design with a gas cushion would be good.
Maybe I should ask Gerry the cost.
Just paid for an expensive holiday so need to be mindful of expenses. It passed the MOT so it’s only me that recognises the current bushes are past their best due to the springs fatiguing and creating coil binding.
I have long since fitted correct length springs of good quality but the damage has been done to the bushes.
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cobraboy
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Re: Polybushes

Post by cobraboy »

There is 2 part liquid poly available for you to cast your own poly bushes. I was sceptical of this product, but after a recommendation from a friend I bought some and re made a shocker bush that had failed after 2 years on my van. It came out really well. I used a 85 shore hardness compound.
Like this
https://www.mbfg.co.uk/QL7572.html?gcli ... gJobfD_BwE
I removed the old bush from the damper and cleaned off all the old rubber, but if doing it again I would leave the outer steel sleeve in the damper. I used a piece of cardboard sheet to form the bottom of the mould and hold the centre tube in place.
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peterc
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Re: Polybushes

Post by peterc »

That’s an interesting option.
I don’t have an outer tube as part of the Bush so if casting remotely would need to create one. Alternatively cast it straight into the shocker end obviously trying to keep the original inner sleeve central.
At 85 shore that’s half way between the standard red and yellow polybushes.
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Re: Polybushes

Post by cobraboy »

That would be easy, just set up the damper level both ways. I used a punch to punch the hole in the cardboard a tad smaller than the centre tube, so the tube was a tight fit. Pushed the tube through the card to get it central in and out. Then to get the tube in the middle and hold it there super glued the card to the outer sleeve. This sealed the bottom of the mould, I then cut the card off with a blade after.
To make it perfect to look at, when gone off I topped up any anomalies on the lower face with a tad more poly.
You can go harder on the shore if you wish, but 85 is pretty solid.
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