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Suspension bushes - bolt to bush clearance


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Afternoon all. Am doing some tinkering with the front suspension on my spitfire and have been comparing lower wishbone bushes. I've got some NOS Quinton Hazell rubber bushes, Polybush (blue - from Canley) and some modern nameless rubber items. The QH ones have a noticeably tighter fit between bolt and steel inner sleeve than either of the other two and I wondered if this was something anyone else had noticed, and whether it matters.

On the lower wishbones it doesn't add up to much movement but on the rear radius arms (same bush size) it seems a bit more significant. 

I'd use the QH but only have 3, and can only find more NOS at £10 each, which is a bit steep.

Maybe it doesn't matter but wondered what others think.

Pete

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Hi Peter,

 Ideally the bolt should be a nice sliding fit in the steel tube.

However have a look at what is moving what and where.

Idf there is a stonking great spring holding it on one direction then it may not matter. If the bush can move back/forth then slack may not be handy.

 

Roger

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As Roger says, ideally a snug sliding fit.  Once installed though, it shouldn't make any odds as the tube should be clamped tight.

My experiences with nameless rubber items (pretty much any rubber copy part made this century in fact) is that the "rubber" isn't what it ought to be in terms of longevity.  Whether the QH branded stuff is any better..... who knows.

That said, I've also been underwhelmed by the longevity of the polybushes on the Vitesse.  Superflex items from Mr Witor himself.  Rearwards one seem to suffer worse.  Mechanical distress rather than material aging.

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46 minutes ago, Nick Jones said:

As Roger says, ideally a snug sliding fit.  Once installed though, it shouldn't make any odds as the tube should be clamped tight.

Ah right, I wasn't sure if that would be the case. I'm not at the point of reassembling so haven't torqued anything up yet. 

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Thanks Roger & RR, the polybush fits in the wishbone and bracket OK, it's just the bolt through the bush is a slightly slack fit. If the bush sleeve is held in position by the clamping force when it's torqued up I suppose it won't make any difference. But wasn't sure if that was supposed to be the case.

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I used not the "normal" supension bolts but much longer bolts. Thus within the Polybush sleeve there is no threaded part of the bolt. As the not threaded part is thicker than the threaded part, a much nicer fit.

Cheers

Martin

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It's the right size (3/8) and is what the usual suspects all sell for that location - definitely a bolt not a set-screw! In any case it's the same bolt in either bush and it definitely wiggles more in the polybush and modern rubber bush that I've tried it in. 

Could do with a longer shank though as Martin suggests - I've seen the same suggestion on John Wolfe's site http://www.wolfitt.com/wolfitt_products_1.htm#Front suspension bolts (upper and lower). However wouldn't this run the risk that you weren't clamping the bush in place if the nut is up against the end of the threads?! Maybe I've over-thinking it... 

Pete

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On 4/25/2020 at 6:01 PM, Nick Jones said:

That said, I've also been underwhelmed by the longevity of the polybushes on the Vitesse.  Superflex items from Mr Witor himself.  Rearwards one seem to suffer worse.  Mechanical distress rather than material aging.

I am not familiar with the Vitesse but have a more general point to make Nick, if I may.

Some designs are rubbish and fitting replacement bushes of different materials won't change that.
I have an example below:

:IMGP2736.thumb.jpg.4857e0ffbeb5d2a95645bf4413f18811.jpgIMGP2737.thumb.jpg.ea48db615e26358063483104238138f5.jpgIMGP2738.thumb.jpg.8c9c2acc31a0279ba8d17cf558bb1619.jpg

This is where the tie bar is mounted onto the front subframe of a Triumph Dolomite.
The first photo shows that it is simply a round hole so there is nothing to prevent sideways/up and down movement other than the clamping force,
resulting in destroyed bushes as illustrated. (It also destroys the tie bars, I can post a photo if anyone wishes?)
You can buy polyurethane bushes for this application but the problem stays, although perhaps the bushes do last slightly longer?

As it turns out, although they did nothing to the production cars, Triumph were very aware of the problem and actually solved it really well.
For the race cars they used a better design of bush. It is actually very similar to the T2000 tie bar bush.
However on its own the redesigned bush does not entirely solve the problem, you need to weld on a (to use its full title)
Tie Bar Locating Cup Washer as well, which keeps the tie bar centred.
(Triumph actually used shortened T2000 tie bars, which is a worthwhile upgrade because these are stronger.
T2000 tie bars are prone to fail at the TCA mount but they can be reinforced, said reinforcement will, by coincidence, make them a snug fit
on to a Dolomite TCA).

 

 

 

Ian.

 

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  • 6 months later...

 

On 4/27/2020 at 1:36 PM, PeteStupps said:

However wouldn't this run the risk that you weren't clamping the bush in place if the nut is up against the end of the threads?! Maybe I've over-thinking it... 

Pete you can always use a couple of thick washers, to stop the nut running against the end of the thread

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