Originally Posted by gfk_velo

When you say it won't take up more than one gear per shift, do you mean that when you push the finger lever (lever 2) all the way across, it will only move you one sprocket at the rear "easier", or do you mean that a full stroke on the thumb lever will only move you one sprocket "harder"?

Is it *really* a sudden thing, or has it been getting progressively worse? The most likely cause would usually get gradually worse, or, you'd leave the bike un-ridden for a while (maybe wet, or maybe with perspiration accumulated on the levers), then come back to it and find that you had this problem.

If you consider how the shift mechanism is triggered by the levers, the reason is clear.

The shifting itself is actioned by the cable either being wound around the cable bushing (pushing lever 2 across), or the cable bushing being driven the other way whilst the spring in the rear derailleur tries to pull the cable through the housing (pushing lever 3 down).

Both levers 2 and 3 have a two stage action. In the first part of the movement, you are working against a small, light action spring, to move a drive pawl into contact with a drive ring.

In the case of L2, the lever pivots slightly at the top against a spring built into the very top of the lever, so bringing a pawl into contact with the drive ring. Lever 3 does the same, the first 10 -15 degrees of motion are against a small spring with the part of the L3 assembly that pivots being allowed to move "down" to bring a pawl into contact with a drive ratchet built into the cable bushing.

If those pivots are "sticky", usually as a result of corrosion, it can be that the pivot action of the lever that allows the pawl into contact with the drive ring needs a lot of resistance before there is enough counter-force to drive the pawl against the drive ring / ratchet.

It's unusual, unheard of, even, for that corrosion to happen suddenly in a bike that is used daily, or even a few times a week ... although it can get progressively worse even in a regularly-used bike (my winter training / turbo bike does it if I don't drop a small amount of oil onto the L3 pivot and work it in once every couple of weeks in the winter).

Another possible cause which is fairly rare but would give you an overnight failure, is normally partnered with slightly flaky shifting all around, is a failure of the either the return spring at the back of the lever (very, very rare) or a failure of the post on the spring mount ring that it hooks around (not so rare but still not something we see very often).

The reason this causes a problem is because the whole spring mount ring can rotate about 10 degrees inside the lever - this is what allows the slight overshift that you need to go from a small sprocket to a bigger one - the gear actually goes past where it needs to be and then settles back onto good alignment under the sprocket. The return spring is responsible for "helping" the mount ring back, amongst other things. If the spring fails or if the post it hooks around breaks, the mount ring will rotate those 10 degrees but not necessarily be pulled back. Added to the 10 to 15 degrees L2 needs to move before the pawl engages out of a 45 degree / 3 gear total motion and you have the ability to shift only one, or occasionally 2 sprockets at a time.

A full strip, clean, lube of the pivot points and inspection of the parts will show you the problem. The guys at Branford will certainly be able to sort this for you. Very few parts of the 10s levers of that generation are unavailable, even now ... the cable bushings and body shells are all finished from the factory (though complete lever bodies are still on inventory, so at VeloTech we just buy those and frag them) and one or two of the smaller spacing / shim washers - but all of the other parts are still to be had.

Hope that helps!

Safe miles, and thanks, Drew, for the name-check!