DIY Poly bushings.

[Tuga2112]

I dont like the price of a full set from SJ.. specially considering what i can get is a mixture of poly and rubber,

now i understand a large amount of owners wants to shy away from poly. but the reality is that poly is what can be easily DIY and theres many different shove harndness values available as well.

I Had some success already with a rear raft bushing. the process is time consuming but not hard. although getting a perfectly centrered fitting is a lot easier when you can 3d print your own mould.

this is not a vague "is this worth doing" post. i am asking if anyone knows about the topic enough to steer me away from what would be an "obvious" mistake from experience.

I Have access to a lathe as well which im going to use to make new sleeves. the metal bar is not cheap. but still considerably cheaper than the alternative. not to mention at the end of the process i will have another set of skills worth bragging about.

pictures of the bushing i already made. this one was reusing theoriginal sleeve. but the full set will certainly contain new metal as not all sleeves come out clean and reusable.




This is likely to be a project that will actually pick up after the summer when the NA goes back in the garage for its suspension work. but for now. im just letting people know of the plan, and will be gathering information as i go along.
If theres enough interest. i can make extra bushings as i go along . maybe even end up supplying a kit for a few people who may be interested.

[FunElan]

I love the idea certainly. I'm installing almost all poly right now.

But I get the sense that the rear raft bushing being soft is the main reason the car handles so damn well. I think if you can find a poly that's soft enough, great. But there may be a reason that the raft bushings are the only ones that haven't been recreated in poly by SWLC/SJ.

If that rear raft bushing is let's say, 50% more stiff than stock, I wonder how much negative "Fwd" effect we would feel in the steering.

[dapinky]

I looked at this many years ago, and decided that as the raft bushes are so critical to the way the car behaves, whilst the OE rubber ones are still available, I will use them.

That said, the bushes themselves are pretty simple (to my inexpert eye) - and it *should* be a matter of establishing the shore rating of the original rubber, and the 'depth' of the actual bush needed to replicate the characteristics of the original.

When I developed the other front suspension bushes (top wishbone and bottom wishbone, and the rear wishbone inner and outer) I was in a position to spend a fair while with Chris Witor who was the sole UK importer for Polyflex. By going through all the stock he had, and could get, along with the lathe processes to suit them, we came up with a solution to match the OE specs. Due to the financial cost of tooling up for production (it wasn't feasible to make them individually on the lathe) it was beyond my means and the rights to stock/sell them were transferred to 2 dealers who still sell them under their own labels.

Since moving to Wales I no longer have the opportunity to drop in to see him and do the work needed to get the raft bushes made. Establishing the shore rating is a simple matter if you have the right probe thingy, a set of measuring callipers and a calculator - not impossible to make a fair guess at it anyway, but not something that I wanted to do.

The great thing is that technology has moved on substantially, and casting bushes at home is a simple process - especially if you can 3D print the moulds. The liquids needed to get the right shore rating can be blended to get the exact requirement, and it is all possible in the average kitchen (a vacuum chamber is preferred, but not essential, although it will give more consistent results).

I'm not sure that a metal external sleeve is even required, as machining that to be a perfect interference fit is not as simple as just casting the poly to fit directly into the raft.

[Tuga2112]

i would like to find the exact shore hardness of all the bushings. but unless that can be done with them already installed. i dont have new bushings at hand to take readings from (my yellow car set is about 2-3 years old, would be a suitable starting point)

[dapinky]

Any rubber can/will become softer and more pliable with age/use 0 so it is important to take readings from as new an item as possible.

That said, if it gets measured at 75 Shore, it is a fair guess that the original was 80 Shore (there is only a limited variety of numbers used in bush manufacture).... I know that anything *could* have been made bespoke, but it was pretty much likely to be 80 or 90 Shore....... any variation in 'bendiness' would be accounted for in the dimension of the bush to give the movement required (a 10mm thick bush would give more movement that a 15mm bush of the same diameter).

Maybe I'm severely overthinking the whole ting, and we should be looking at it in the same way that I look at shocks/springs.......

...... and that is to think that "anything new that is slightly wrong in specification will still be better than something that has been used for 30+ years".

In a very unscientific method, something simple like pass a 300mm bar of 12mm diameter, through the bush (held securely), and apply a 15Kg force horizontally to the end of the bar,,,, then measure the distance that the bar has moved.

Make a selection of bushes in 80 Shore material of various thicknesses, and do the same experiment to establish which depth gives the same movement.....

..... job done!

eg, use the mold you have to make an 8mm bush, a 12mm bush and a 16mm bush..... if the bar moves 25mm on the OE bush, and 30mm with the 8mm one, 27mm with the 12mm one and 22 with the 16mm one it is reasonable to believe that you need a bush 13mm thick! - yes, I know it needs a number of measurements under the same conditions, and take an average..... and that it isn't going to be a linear result line, but you know what I mean!

Still, looking at the state of the one you replaced (in the video you sent me), you would have seen an improvement by squirting some silicone sealant into the gap!!!!! (just suggesting that I am severely overthinking it, and anything you can make would be far better than something worn to excess..... but remember to change both sides of the car at the same time (if reasonably possible) to keep it all balanced!