Its a shocking question (which way is up)

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Anthony Drake
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Its a shocking question (which way is up)

Postby Anthony Drake » Thu Feb 21, 2008 6:06 pm

Whats the go with the position of the shocks on old twinshocks.
Is there a right and wrong way to fit, up or down ,top or bottom.
I would have thought the skinny bit of the shock goes to the top.
But alas I see malcom's collectable TY 175 the skinny bit goes to the bottom.
Whats the story?.
Please could someone clarify this for me.
Thanks Drakey


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Starky
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Re: Its a shocking question (which way is up)

Postby Starky » Thu Feb 21, 2008 6:59 pm

Hi Anthony,
My Falcon shock came with the instructions that the units operate with the "skinny" end down . As for the technical reasons behind this magic, I am sure David Lahey will have the info he will be along shortly. I have no idea.

I read the instructions for once and followed them. I know I will be ostricised from the ranks for reading instructions :oops: I promise not to do it again.

Starky
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Re: Its a shocking question (which way is up)

Postby PA » Thu Feb 21, 2008 7:01 pm

Instructions are only to be read after all other means have been exhausted. Shame, shame, shame.



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Re: Its a shocking question (which way is up)

Postby David Lahey » Thu Feb 21, 2008 9:12 pm

Anthony Drake wrote:Whats the go with the position of the shocks on old twinshocks.
Is there a right and wrong way to fit, up or down ,top or bottom.

Yes there is

I would have thought the skinny bit of the shock goes to the top.

On some shocks yes

But alas I see malcom's collectable TY 175 the skinny bit goes to the bottom.

Yes that's probably right for those shockies.

Whats the story?.
Please could someone clarify this for me.
Thanks Drakey


The piston has to stay in the oil and there has to be a way of accommodating the change in internal volume of the shockie as it moves. Compressing and expanding a small volume of gas is the usual way to provide for this requirement. The volume of gas required is determined by the diameter of the rod, the travel of the shockie, and the pressure range that the rod seal should be operated within.

Shockies with a gas space that is in direct contact with the oil have the gas at the top.
Some achieve this with the rod at the bottom and some with the rod at the top (same as for forks -some are "conventional" and some are "USD").

Standard Falcons are designed to work with the body up. There may be a slight suspension action advantage in having the rod at the bottom due to the rod assembly being lighter than the body (ie reduced unsprung weight). Many other shockies work perfectly well with the rod end up and Falcon will make specials that work rod end up for people who like the look.

Standard Falcons of different lengths are all made to have 4" of travel and so they all have the same length rod. To make the different overall eye to eye lengths required, they make different length bodies. To make this design work, the rod has to be at the bottom, or the piston would move out of the oil when the shockie extends out past a certain length.

Some shockies do not have the oil in contact with the gas. They might have a rubber bladder (B and C model Yamaha monoshock) or a floating piston (called the de Carbon method), or the gas may be stored within a piece of closed cell foam. In these type of shocks, it doesn't matter which way up they are mounted because the piston will always be in oil.

The shockies on Yamaly's TY175 appear to be the type of Betors that are usually mounted rod end down but I have seen them used in the rod end up position too on other bikes. They may not be Betors. It's hard to be sure from the photos.


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Anthony Drake
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Re: Its a shocking question (which way is up)

Postby Anthony Drake » Sat Feb 23, 2008 8:39 pm

Thankyou David
Drakey


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