Bush hardness question

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Bush hardness question

Postby Kraken » Sun Dec 09, 2018 8:04 pm

Hi guys,

I'm dismantling a subframe at the moment (OHV) and thought I would replace the bushes while I'm at it. Prices seem to be very high for a full set of bushes (although I've not checked club price yet) but my dad thinks he may be able to cast some for me.

The polyurethane he currently possesses has a shore rating of 70-72, would this be a fine for a road going 1159?

Thanks,
- Callum
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Re: Bush hardness question

Postby fistfullofV5's » Sun Dec 09, 2018 9:24 pm

Hi , my SuperPro (Aussie) poly bushes range from 70 up to 90 shore hardness. The softer material being for the shock mounts and harder for the wishbones and trailing arms. I've got a 2litre ohc Firenza. I'm not sure that the lower hardness poly would be ok for suspension use. I'm basing this opinion on the knowledge that many suspension poly bushes are in the 80 to 90 range. Someone else may well known better than me. You’re also right that full bush kits are expensive. Rubber bushes for the Jensen Healy which uses Viva suspension are available from here https://www.martinrobey.com/jensen-healey/
You could get your Dad to make some and fit them. If they're not hard enough, it should fairly easy to spot.
Regards, Dave.
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Re: Bush hardness question

Postby 1972nail » Sun Dec 09, 2018 10:05 pm

The shore hardness for the standard rubber bushes range from 40 to 60, 60 being used on the rear arms of the HPF as standard. I've been told that lower shore rating polyurethane tears easier than rubber of the same shore rating and that's why polyurethane bushes are generally quite a bit harder than the rubber equivalent.

There are mixed opinions on polyurethane bushes and their suitability on road cars. Some say they are very harsh and can make the handling quite choppy while others think they are superb. Personally I have only fitted them to my castor control arms and front lower inner wishbone pivots to withstand the extra loads that my 9x15 front wheels put on the front suspension.
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Re: Bush hardness question

Postby droopsnoot » Mon Dec 10, 2018 11:18 am

The other thing to keep in mind with poly bushes vs. rubber ones is that, in some locations, they work differently. In a standard rubber bush - for example the front lower wishbone bush - the rubber is bonded to the inner steel sleeve. The suspension bolt is tightened onto that sleeve with the weight of the car on the wheels, and the only rotation of the arm is the "give" of the rubber, as nothing else moves. With a poly bush (or with all the ones I've seen, at least) the inner sleeve is not bonded, so you have a lot more movement of the arm allowed by a poly bush.

I've got poly bushes in the rear of my Firenza, and maybe in the castor arms (where nothing else is available), but when I put the hatch together I just went with standard rubber ones where I could get them. I would say that the ride on the Sportshatch is much "softer" and certainly more comfortable, but there are lots of differences other than the bushes - standard dampers vs. Spax on the HPF, standard Magnum springs, recent (<2 years) rebuild vs. 20+ years ago.
My real name: Mike. My web site: http://www.firenza.net

My stuff for sale: http://www.firenza.net/forsale.shtml
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Re: Bush hardness question

Postby Kraken » Tue Dec 18, 2018 10:15 pm

Thanks for the input guys. I would actually prefer rubber bushes but I think a full set will be out of my budget. I'll message club spares though and see. Will definitely look at moulding bushes though, could be handy with 3 Vivas in my ownership now :oops:

As for the steel sleeves being bonded, they should be bonded with the way we are planning on casting them. The plan was to insert the sleeve into the mold and cast the poly around it and hopefully it should adhere properly.
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Re: Bush hardness question

Postby 1972nail » Tue Dec 18, 2018 11:23 pm

Have a look at Chris and Joe's project. Here's the relevant page.

viewtopic.php?f=23&t=24431&start=20
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Re: Bush hardness question

Postby chrismc » Sat Dec 22, 2018 10:39 pm

Blast from the past David. :lol:

Yes these are still going strong. No problems at all. The ride I would describe as 'firm' rather than harsh. Certainly no hardship and maybe a bit sporty? 8) :lol:
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Re: Bush hardness question

Postby Kraken » Sat Dec 22, 2018 11:37 pm

Yes I had considered messaging you Chris...

When I realised it was your dad that had made them then I decided not to. Feel bad enough forcing work upon my retired father, never mind somebody else's!
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