Another Chainring question.

u_i

Active Member
Location
Michigan
its apparantly quite easy to file an extra slot into the old style 2 speed left shifter to create an index for the 3rd gear
I never saw any evidence of this getting done successfully in practice. From my my own inspection an attempt to file an extra slot has no chance of accomplishing anything and will just irreversibly damage the shifter. 3-speed shifters can be had for cheap and there is an advantage in being able to go back to the previous configuration, if the new one fails to work out. There is an advantage in going with an indexed shifter in that the pusher should be set so that it is not rubbing the tensioner wheel in either of gear positions and thus refrains from damaging that wheel in the long term. This is trickier for 3 speeds than 2.
 

kais01

Regular
Location
Sweden
i reckon the shifter can take some filing.

but balancing the derailer for the middle sprocket will be hard because there is no direct connection between the cable and derailer; it is suspended in both directions.

reason for this i have guessed is that you can use the shifter without damaging the mechanism also at standstill. nevertheless makes it hard to find a middle position.
 

u_i

Active Member
Location
Michigan
reason for this i have guessed is that you can use the shifter without damaging the mechanism also at standstill. nevertheless makes it hard to find a middle position.
Whether or not you can shift when not moving depends on the gear side. Incidentally even with sprockets, though you shift while standing, the shift is completed only when you start moving. In any case, I use the same SA shifter for the hub and sprockets, not the same as original Brompton's, but functionally equivalent.
 

u_i

Active Member
Location
Michigan
I was able to make the the SA 3 speed indexed shifter work. The index points are off for the rear derailleur. SR friction shifter works great. 3-speed is nice upgrade. I used Bikegang kit.
Index points for 3 speeds can be set incorrectly, but should not be off as a matter of principle. For 3 speeds you set the middle position by cable length and high and low by limit screws. The tolerances for mthe iddle are very narrow for Brompton with 3 speeds. Even though the friction shifter may seem to work fine in short term, you should examine the top pulley of the tensioner, after a more extended use an look for thinning and ridge developments near the pulley's circumference. The Bikegang kit is indeed fine. They could have added a shim/washer to prevent locking of the tensioner against the outer sprocket.
 

u_i

Active Member
Location
Michigan
I have the limit screws set up well. So are you saying the tension is incorrect?
SunRace thumb shifters lack cable adjustment and there is no fine adjustment on the Brompton pusher side other than by securing the screw on the cable that works very coarsely. The solution are add-on barrel adjusters such as by Ritchey or Jagwire. One can also place inline adjusters on cables but these are less convenient on Brompton, due to the complicated cable layout, than adjusters placed on shifters.
 

Schwinnsta

Active Member
I have already added an inline adjuster. So are saying that it is a matter of getting the tension just right or does it have to with spacers? It seems like the amount of cable pull (distance) of the indexed three speed is off.
 

u_i

Active Member
Location
Michigan
Yes. You can set the shifter in middle position, flip the bike upside down and tweak the adjuster so that the chain is on middle sprocket and the tensioner wheel stays clear of the pusher's fingers. Then you can put the shifter into either of the extreme positions and adjust the corresponding limit screw so that again the chain is on the respective sprocket and the wheel stays clear of the pusher's fingers. You can do that without turning the bike upside down, but it is hard to see then whether the wheel rubs against the pusher or not. The tolerances are tight.
 

Schwinnsta

Active Member
Yes. You can set the shifter in middle position, flip the bike upside down and tweak the adjuster so that the chain is on middle sprocket and the tensioner wheel stays clear of the pusher's fingers. Then you can put the shifter into either of the extreme positions and adjust the corresponding limit screw so that again the chain is on the respective sprocket and the wheel stays clear of the pusher's fingers. You can do that without turning the bike upside down, but it is hard to see then whether the wheel rubs against the pusher or not. The tolerances are tight.

Thanks. I will try it. Does you have tension in the cable when it is on the 12T cog?
 

u_i

Active Member
Location
Michigan
Actually, no tension on the smallest cog and a lot of excess slack. I worked to contain the excess length within the run of the cable. However, with SunRace shifters the simplest might be to let the excess stick out of the shifter.
 

u_i

Active Member
Location
Michigan
The company name is now SunRace Sturmey Archer. My impression is that they name the shifters Sturmey Archer when they market them for hubs and SunRace otherwise. The tricky part of the shifters for hubs is that increments in the cable pull may be uneven between gears. This should not matter for 3 speeds because of the way you tune the shifting, but can matter for more. I use 3-speed Sturmey Archers both for the hub and for the sprockets.
 
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