F: Frame Rear seat stays friction

[Simon Dinsdale]

Just been rebuilding a set of seat stays for my Shadow which got me thinking (I know that's dangerous). On the series B's without a rear damper these are the only rear suspension damping which can be adjusted by the damper knobs and was the original reason for their design. On a series C the rear suspension has a hydraulic damper so the seat stays should really be set so they are free to move with no friction, but not too free so they move sideways. If they are set too tight the friction in the seat stays will affect the operation of the hydraulic damper in a similar way to what Greg found the friction in the front suspension lower link eccentrics affects the front suspension. So has anybody considered replacing the friction material in the seat stays drums with a bronze bush on a series C and lock the damper knob adjustment or does everybody just set them to minimum friction possible without been too loose?
I remember years ago with my Rapide when I changed to a fully floating seat / pannier frame discovering that the bike suddenly had rear suspension. The only change to the suspension was the seat stays were no longer been used so were not stiffening the suspension up.
To me the seat stays appear to be a leftover design from before the hydraulic dampers were used and if you intend to use a decent damper like the Avo then you don't want the seat stays interfering with the hydraulic damper operation.

Reason for asking is I've not used seat stays for the last 25 years.
Simon

 

[davidd]

Simon,

I have always been surprised that the seat stays remained on the Series C Vincents. The stays are complicated, costly and unnecessary if you consider that Vincent used the most advanced suspension design they had on the 1950 Grey Flash TT bikes. That was two struts from the foot pegs to support the seat. After the TT they tried other rear suspension designs, including a cantilever seat that had no other means of support other than being attached to the UFM.

I assumed that the complicated and expensive seat stays had become a notable marketing tool or a symbol of unique design that Mr. Vincent felt he could not give up until the serious cost cutting of the Series D model came along.

David

 

[Chris Launders]

I have an AVO coil-over on mine and the dampers slacked right off, as you say just enough to stop them flopping about.
Chris.

 

[Bill Thomas]

Just been rebuilding a set of seat stays for my Shadow which got me thinking (I know that's dangerous). On the series B's without a rear damper these are the only rear suspension damping which can be adjusted by the damper knobs and was the original reason for their design. On a series C the rear suspension has a hydraulic damper so the seat stays should really be set so they are free to move with no friction, but not too free so they move sideways. If they are set too tight the friction in the seat stays will affect the operation of the hydraulic damper in a similar way to what Greg found the friction in the front suspension lower link eccentrics affects the front suspension. So has anybody considered replacing the friction material in the seat stays drums with a bronze bush on a series C and lock the damper knob adjustment or does everybody just set them to minimum friction possible without been too loose?
I remember years ago with my Rapide when I changed to a fully floating seat / pannier frame discovering that the bike suddenly had rear suspension. The only change to the suspension was the seat stays were no longer been used so were not stiffening the suspension up.
To me the seat stays appear to be a leftover design from before the hydraulic dampers were used and if you intend to use a decent damper like the Avo then you don't want the seat stays interfering with the hydraulic damper operation.

Reason for asking is I've not used seat stays for the last 25 years.
Simon

I asked the chap who started all this fork mod, What he did with the rear, He said he Put bearings in there, I might try that on my standard Comet this year if I have time, I like the look. Cheers Bill.

 

[vibrac]

Even with bearings in the pivots the wheel still has to lift the weight of the passengers 'on its own' rather than sharing the load over the entire bike /both wheels with a fully sprung seat
Or is there a fault in that logic?

 

[Simon Dinsdale]

Even with bearings in the pivots the wheel still has to lift the weight of the passengers 'on its own' rather than sharing the load over the entire bike /both wheels with a fully sprung seat
Or is there a fault in that logic?

When I noticed the difference going to fully sprung on the Rapide years ago I rarely carried a passenger at the time so passenger weight was not a factor. The rider will have an affect but not as much.
What I'm noticing is the suspension takes a lot of initial effort to move due to the friction in the seat stays. Once it starts to move and that initial friction is overcome then the suspension moves, but that is the opposite to how a hydraulic damper wants to operate.

 

[Simon Dinsdale]

I've had a look and cannot find a bearing (ball or needle) that will fit inside the seat stay drums without modifying the casting which I'm not willing to do. I have found an oilite bronze bush that will fit with a little modifying on the lathe so will order some and have a go. To me it just looks wrong to use friction band material as the bearing surface if you want to reduce the friction.
Simon

 

[Bill Thomas]

Even with bearings in the pivots the wheel still has to lift the weight of the passengers 'on its own' rather than sharing the load over the entire bike /both wheels with a fully sprung seat
Or is there a fault in that logic?

You told me not to question, Thems that know better than me, I asked the fork man what he did to make his bike so good, This is what he said. Cheers Bill.

 

[timetraveller]

Simon, it is possible to buy PTFE strip which has one side of it etched so that an adhesive can be used. If this was epoxied inside the aluminium part, so that it was free to rotate on the steel inner, it would probably save time and machining effort. PTFE, in this use has a very low friction.

 

[bmetcalf]

Loctite the knobs on if you slacken them! They may still be unobtanium.