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Mystery suspension components

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Getting to the bottom of my basket of bits supposedly being components from a 1956 Dommie 99 when I came across these pictured items that I do not recognise. Can anybody help with identification?

Regards. Ron T.

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... and as if they've been attacked with a hacksaw. Look at the undercuts on those fork caps.

Hi Ian I don't think that the ferrules have been modified in any way, the "undercuts" are sized and shaped to form a seat for the stop on the shocker. The register fits exactly into the undercut and, when the ring is rotated, the curved top forms a seat for the same stop. With the shocker seated in the undercut the spring would be fully extended. When the ferrule is turned and the shocker registers on the curved leg top the springs are pre compressed to give a harder ride.

 

 

 

 

 

 

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I see. Still look a bit rough to me.

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The chrome rings look like the preload adjusters from Armstrong suspension units. Armstrong would have been original equipment in 1956. The suspension units were fitted with 2 springs one short, one long (as in your photo). The longer spring is the top one and the adjusters were fitted between the 2 springs with the "prongs" pointing downwards. In one position both springs are in use. In the other position the "prongs" sit on a collar on the body of the unit so preventing any movement of the lower spring ie all the suspension load is carried only by the longer spring. I can't quite tell from the photo but the bodies of the suspension units could also be Armstrong. Do the "prongs" fit into matching gaps in the collar? These units would have been fully shrouded. Shame to hide those purple springs! If you want original suspension units for a '56 bike (twins & singles) these are the units to keep.

Ian McD

Spot on Ian. The prongs fit exactly into the collar and the collar has radiused indents to accept the radius on the end of the prongs when the hard ride setting is selected. Unfortunately there is only 1 body unit so unless someone has a matching unit,the set that I have will not be a lot of use.

Really appreciate your input, thankyou. Ron.

Ian, been mulling things over and, as so often happens, something else occurred to me. You said that the units would have been fully shrouded and that it would have been a shame to hide those purple springs but, surely if the units were totally shrouded, it would not have been possible to have the collar located between the two springs would it?

As an aside: when I bought the bike, in bits, the frame, forks and tank had all been newly finished in that dreadful shade of purple. Beautifully done but totally hideous, my first step in the restoration was to have it re blasted and finished in black (not the tank)

Best regards Ron.

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The upper spring has its own pair of shrouds, while the collar doubles up as a shroud for the lower spring. Within the collar there is another sleeve to complete the shrouding between the prongs.

Cheers, Ian McD

Armstrong

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Wow! The knowledge that is held by club members never fails to amaze me. Thankyou Ian, I feel sure that some other members will also benefit from your detailed information.

Best regards, Ron.

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I've certainly learned something. Many thanks.

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Doesl anyone know where I can get softer springs? My '56 rides like a brick. Hydraulics seem to still be working. Thanks

 

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Jim, I wouldn't have expected them to be that firm. Assuming that you have Armstrongs as above which setting do you have them on? The softer setting is with both springs moving ie the prongs of the adusters sitting in between the lugs on the body of the unit. Have you checked that the swing arm is moving freely with the suspension units removed? If the brick-like ride really is coming from the springs I would suggest enquiring with some of the spring manufacturers who advertise in Old Bike Mart. They should be able to wind new springs of a softer rate using your original springs as a pattern. Paul Savage of Redditch made a new girder fork spring for me a few years ago.

Cheers, Ian McD

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The question I have is - which position gives a stiffer spring?  When you have two springs together, as in this set-up, according to the theory I have, you get a lower spring rate than the two separately:  1/R = 1/R1 + 1/R2.  So is the solo position two springs, and the two-up position one spring?

Paul

The stiffer spring is when only one is in use. i.e. the collars are rotated such that the blades on the top collar sit in the indents of the lower collar and take the lower spring out of the equation.

Regards

Dick

 

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