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Double front shock absorber

Many thanks to those who have emailed with information about double front shock absorbers, in response to my wanted post. Unfortunately, gentlemen,you missed the point that I am looking for a shock absorber whose arms connect to the ends of the axle, rather than the more inboard standard Austin locations. Pigsty used to produce these, but have stopped pending introduction of a new design. Meanwhile I am trying to overcome the problem of axle tramp at speed (over 65 mph!) on my Ulsteroid, in preparation for the Vintage Revival at Montlhèry.

Location: Just north of Cambridge

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Re: Double front shock absorber

How did you get your place at Montlhery? I sent in my application in October and despite several mails have had not even the courtesy of a reply!

Location: Ripon

Re: Double front shock absorber

It seems to be a matter of luck, but I think I applied last June, and I got in three times previously. I only got the offer very recently, so I suspect someone dropped out.

Location: Just north of Cambridge

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Re: Double front shock absorber

I remember seeing this image some time back - have no idea if it works or if it is what you are after Bob.

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Re: Double front shock absorber

It looks interesting, but I suspect the damping effect of the two springs would be more use than the very long armed shock absorber, angular movement at the friction discs being minimal.

Location: Just north of Cambridge

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Re: Double front shock absorber

Robert do you mean the set up on page 185 of the green book. I have a similar version of this and I believe it is a Pigsty one.

Douglas

Location: Dorset

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Re: Double front shock absorber

Quote: Ruairidh Dunford
I remember seeing this image some time back - have no idea if it works or if it is what you are after Bob.



Not very effective unless multiple friction discs have been used and then would depend on friction pressure.

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Re: Double front shock absorber

Quote: Douglas Alderson
Robert do you mean the set up on page 185 of the green book. I have a similar version of this and I believe it is a Pigsty one.

Douglas


From memory this does not work as the geometry of the dampers and the axle conflict resulting in a locked axle. One side needs a link allowing the other to act as a very short control rod.

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Re: Double front shock absorber

Quote: Paul Neil-MacLachlan
Quote: Douglas Alderson
Robert do you mean the set up on page 185 of the green book. I have a similar version of this and I believe it is a Pigsty one.

Douglas


From memory this does not work as the geometry of the dampers and the axle conflict resulting in a locked axle. One side needs a link allowing the other to act as a very short control rod.


I have run the green book setup very successfully on my special for over 30 years now. Provided you incorporate rubber bushes in the ends if the arms the change in length created by their arc seems to be of little consequence with the very small amount of moment required for an effective sports/racing setup. I have found it desirable to run the dampers very tight with a comparatively stiff spring otherwise there is a tendency to jack the inside rear wheel in fast tight corners. As mentioned by Paul a link in one end may be preferable for a road car with more standard springing as suspension movement will be far greater. I don't think the long arm setup would provide terribly effective damping but it would fix the roll centre, which is a failing of the other arrangement.

Location: NZ

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Re: Double front shock absorber

I can't really comment on the benefit or not of the setup I have as it's the only setup I have used but I think it is what Robert is referring to.

Douglas

Location: Dorset

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Re: Double front shock absorber

I have seen a picture of a double shock absorber setup with two friction units, one each side of centre, each unit having shortened control arms to suit the original links to the axle. These should be much more effective as shock absorbers, but no benefit for sideways control. Robert, is this what you were originally referring to? Someone in England was advertising them for sale, but I can't remember where I read it.

Location: Wellington, NZ

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Re: Double front shock absorber

Ivan,

I presume these are what you're referring to:

http://www.oxfordshiresevens.co.uk/improving-your-austin-seven/ scroll down the page

http://sky-rocket.net/frames.html click on 'Austin 7' then see page 6 of 7

Jeff.

Location: Almost but not quite, the far North East of England

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Re: Double front shock absorber

ive got 2 sets for full width. twin damper in stock at moment.

www.7ca.co.uk

phone back on monday.

tony 0116 2867522

Location: huncote on the pig

Re: Double front shock absorber

I made mine by cannibalising a couple of standard front shockers and getting a bit of a 4"wide strip of mild steel to make the wider centre plate. It was carefully constructed by putting the outer arms in situ and cutting the centre plate to fit! Not difficult if you have a hacksaw, and angle grinder and some big files. The wider centre plate is a useful mounting platform for the timing strut!

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Re: Double front shock absorber

On re reading your original post, the problem is axle tramp over 65 mph, I doubt the problem is entirely to do with damping. Have you checked wheel balance, play in steering joints and king pins? even slight play in the KP will cause tramp. Is toe and castor correct? What size wheels and tyres are you using, are the wheels true, and what pressure in the tyres?

Location: NZ

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Re: Double front shock absorber

Thanks Jeff, yes that's it exactly. And it would work on my Bantam too. Also, as Charles says, not hard to cobble up.

Location: Wellington, NZ

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Re: Double front shock absorber

Many thanks to all who have contributed to this thread, which strayed well beyond my original request. I have now agreed the purchase of the shock absorber I wanted. I already had in mind to check the other points which have been raised, and look forward to enjoying the Vintage Revival again.

Location: Just north of Cambridge

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Re: Double front shock absorber

HI

I am using the following setup on my special:

https://www.facebook.com/LotusSportster7/photos/pcb.1179072518876922/1179069122210595/?type=3&theater

Here is a picture of the bits:

https://www.facebook.com/LotusSportster7/photos/pcb.1247224022061771/1247222972061876/?type=3&theater

I was advised from a very good source the single shock would do nothing of any value on the front of my special.

James