Sturmey Archer 4 speed Trigger

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Kings
Posts: 12
Joined: 19 Mar 2008, 3:48pm

Sturmey Archer 4 speed Trigger

Postby Kings » 17 Oct 2020, 9:16am

I am using a FM 4 speed hub on my Dawes for Winter riding, the trigger is giving me trouble and I need to replace it. Has anyone going spare that they don't need? The usual problem is the wear means the lowest gear will engage but not hold. Thanks

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simonineaston
Posts: 3579
Joined: 9 May 2007, 1:06pm
Location: Live & work in Briz'l

Re: Sturmey Archer 4 speed Trigger

Postby simonineaston » 17 Oct 2020, 4:25pm

one phrase springs to mind to wit "hens' teeth"...
EDIT: waddya know - there's one on fleabay
ttfn, Simon in Easton
(currently enjoying a Moulton TSR & a nano Brompton...)

Ugly
Posts: 436
Joined: 14 Jul 2009, 8:34am

Re: Sturmey Archer 4 speed Trigger

Postby Ugly » 17 Oct 2020, 5:32pm

This is from the Classic Lightweights Site, I followed the instructions on fettling the lever and it worked a treat.

Sturmey Archer FM – Several people have told me that they have trouble with the Sturmey-Archer FM: they cannot get the bottom gear to lock in on steep hills – just when you need them of course. The secret seems to be to change the normal way into bottom gear, keep pulling on the trigger and start pedalling (spinning freely is no good, some pressure is needed) until you feel the trigger go click as it moves in just a little further. This seems to do the trick and it should hold now.

If, however, the first gear still slips then Bill Ives has sent the following hint:
I have been reading on the Classic Lightweights web site your bit about the difficulty of getting an SA four speed to go into bottom gear. Sometimes even if you can get it in it will jump straight out again. I have heard people say they have to hold the trigger to make sure the gear stays in.

The problem here is that the very high cable tension required means that the pawl which holds the quadrant in place is very likely to jump out and once it has done that a few times it becomes rounded off and so is more likely to jump out and become more worn. It’s a vicious circle.

Here’s a suggestion to fix it:- Remove the cable. Now take a sharp screwdriver and lever the side of the casing out, that’s the side that the cable ferrule screws/fits into. Lever it out just enough to remove the spring which will allow the pawl to pivot out. Using a bench grinder square up the end of the pawl. Don’t let it get too hot or the tempering will be damaged. The spring sometimes becomes a somewhat tired so give a little squeeze in the vice to tighten up the bend. Reassemble and tap the side back into place with a small hammer and with a bit of luck it will now stay in bottom gear.
There are instructions on repairing the FM including exploded diagram at:
http://www.hadland.me.uk/sa/safm.pdf

Kings
Posts: 12
Joined: 19 Mar 2008, 3:48pm

Re: Sturmey Archer 4 speed Trigger

Postby Kings » 17 Oct 2020, 9:48pm

Thanks, I will try that. If the trigger is dismantled ie with the rivets removed then it would make it easier and the ratchet plates could be cleaned up. They are obviously heat treated to give them sufficient hardness so it makes it more difficult to sort out any wear. I will try your suggestion. Thanks