Jumping down gears

[Woz]

Is the cable properly routed at the pinch bolt / allen key on the rear mech?

 

[Polco]

The cable is still tight, relative to the position of the mech. I never thought of checking the skewer was holding firmly, pretty sure it is as I would have thought it would have eventually shifted to rub against the left chainstay? Worth a check though!

 

[keithglos]

Re:

If you stand on the right side of the bike with the pedal forward, then put increasing weight on the pedal you should be able to see what is happening. It could be something like the bottom bracket to seat tube joint not brazed, and easing apart, although I have never seen that.
Keith

 

[Robbied196]

Re:

Its a bit of an odd one without seeing it. If you tap the cable at the downtube you would increase the tension slightly, so it shouldn't drop down. Is the 'L' limit screw against the casing when you are on the big sprocket? Does the derailleur have a 'B' screw adjustment?

 

[Polco]

Re:

The limit screws have been adjusted to work but haven't checked if it's against the casing, I have adjusted the b screw but the same results whatever the position.

 

[oonaff]

any luck mate ?

 

[Polco]

I've convinced myself it's the cable run or frame flex at the root of the problem, wondering if using this will help.
http://www.ebay.co.uk/itm/Sturmey-Arche ... 1046455961

 

[oonaff]

so you checked the chainstay welds that kieth said to and they are ok ?
at least that wheel you are considering, would prove its the cable guide and not the stays flexing.
but what could you use to file out the old cable guide ? some one must have had that problem before
renovating a well rusty frame..some kind of abrasive string ?

 

[Polco]

As far as I can see the brazing around the bottom bracket is sound, the frame was sandblasted before repainting and it looked good. Cable guides are metal and part of the bottom bracket shell, I've given the guidle a good clear out so cable moves freely inside.

 

[oonaff]

graphite grease ? if the cable is moving freely what is going on ? surely if the chain stays are flexing that much
the rear wheel would rub on the brake blocks