Thumbshifter slipping

[User482]

Hi everyone, here's a bit of an odd one:

My commuting bike has 9-speed Dura Ace thumbshifters fitted to flat bars via adaptor mounts. These: http://www.wiggle.co.uk/shimano-dura-ace-7700-9-speed-bar-end-lever-set/
http://www.paulcomp.com/thumbies.html

The problem I have is when in the big ring, the front derailleur (Deore M611) spring keeps pulling the shifter back so that the chain rubs against the derailleur. There's no provision for adjusting tension that I can see, and I've tightened the shifter mounting bolt to the point where it's starting to round off.

Any ideas?

 

[slowmotion]

Would fitting an in-line barrel adjuster help with the problem? Apologies if I have misunderstood.

 

[sittingbull]

Presumably you've tried lifting the half-round ring (visible in link) and switching between indexing and friction shifting? My initial thoughts are that there's not enough friction within the shifter and the front mech spring is pulling the cable back.

EDIT: reviews say front shifter is friction only, presumably friction is adjustable.

 

[Yellow Saddle]

It sounds to as if your High Limit screw on the FD is fighting with the shifter's relatively weak retention system and winning the war. Turn the High Limit Screw slightly out - 1/4 turn at a time - until the problem disappears. There is a sweet spot where it doesn't pull the shifter and where it doesn't push the chain off the crank.

I assume by "Shifter mounting bolt" you mean the bolt that controls the shifter's clutch?

 

[User482]

Would fitting an in-line barrel adjuster help with the problem? Apologies if I have misunderstood.

The mount has a barrel adjuster - I've tried in both directions and it doesn't seem to make any difference.

It sounds to as if your High Limit screw on the FD is fighting with the shifter's relatively weak retention system and winning the war. Turn the High Limit Screw slightly out - 1/4 turn at a time - until the problem disappears. There is a sweet spot where it doesn't pull the shifter and where it doesn't push the chain off the crank.

I assume by "Shifter mounting bolt" you mean the bolt that controls the shifter's clutch?

Thanks, I'll try that. The bolt fits through the centre of the shifter and into the mount below. I don't think it has any function other than holding it in place.

One further thought: do 10-speed mtb derailleurs have a higher spring tension than 9-speed? I never had this problem on my old bike when the shifter was paired with a 9-speed XT derailleur.

 

[srw]

Check your cable runs. I had the same thing because the cable was too close to the brake and so the friction in the shifter couldn't hold it.

 

[User482]

Check your cable runs. I had the same thing because the cable was too close to the brake and so the friction in the shifter couldn't hold it.

Cable runs seem fine, but good tip.

@Yellow Saddle was on the right lines: I adjusted the limit screw and it did stop pulling the shifter back, but only well past the point where it would unship the chain if shifting to the big ring.

I'm going to fit a replacement bolt and washer to the shifter to see if I can cinch it down a little more - it's difficult to tell how tight it is because the existing bolt is made of cheese and I don't want to round it off. The action in the shifter does seem lighter than it used to be.

 

[Yellow Saddle]

Are you sure you are attempting to tighten the clutch and not the internally expanding mount? Post a picture please, lets see.

 

[Yellow Saddle]

Are you sure you are attempting to tighten the clutch and not the internally expanding mount? Post a picture please, lets see.

Actually, I see you've already posted a picture of the mount itself. I'm sure you're on the right page.

 

[User482]

Update: I used a hacksaw to cut a slot across the bolt, and tightened it with a screwdriver. It's not perfect, but definitely less slippage.