Gearbox stopped selecting

[Pete.]

Riding in to work this morning I pulled up at some lights, when they went green I pulled away, went for second gear, found neutral and then could not shift up nor down. At first I thought the lever had come loose on the gearbox spigot but that's all tight. I have spring pressure on the lever both up and down so it's centering but it's clearly not operating the shift drum.

I'm not so familiar with the internals of the shift mechanism so I can't visualise what might have gone wrong. It's not the splines that much I know because with over 100k on the bike they still looked like new at the last clutch change. Besides, the shift lever is not behaving how it should. It behaves the same as if you're already in top gear and go for another, except it's doing it in both directions.

Any ideas? Anyone got some good photos of the mechanism from the input shaft to the drum?

Thanks

[Pete.]

I've found this schematic in a manual online. I think that the spring no6 has failed or come out.

Capture.PNG (133.77 KiB) Viewed 4116 times

The spring (6) pushes the guide plate (3) forward so the hooks catch on the pins of the shift drum. Since the centering spring (1) is clearly working I can only assume that the guide plate (3) is either stuck in the rearward position because it's jammed on a burr or foreign body, or the spring has failed.

I'll fnd out on the weekend when I get the box apart.

[FuzzyEdges]

Ooh, good Investigation work Pete.

[Pete.]

Well, it would be if I paid attention

I was obviously quite flustered when I broke down and then had to walk the last mile to work in full motorcycle gear so I was thoroughly cooked by the time I got there.

Anyway, I picked the bike up today and had another look at the gear lever. It's wasn't actually centering just moving up and down with no resistance. I've recovered the bike to my place and got it stripped down and found the fault. I'm just popping out but I'll be back later to report what was wrong and how I fixed it.

Pete.

[Pete.]

So basically the gears had stopped selecting because - the selector had broke! These two parts had obviously been resistance welded but they had parted at the weld.

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So I gave them a quick file test to check the hardness. Not hardened at all so no problem welding them. Out with the tig and 5 minutes later they are glued back together.

selector welded.jpg (210.44 KiB) Viewed 4072 times

I gave the gear cases a good clear out with brake cleaner and a 2" paint brush then re-assembled the selector ready to fight another day.

selector re-assembled.jpg (260.07 KiB) Viewed 4072 times

Quite happy now as I was looking at getting a replacement gearbox. Instead I spent the money on a new friction plate for the clutch since it';s such a big job to change I thought I'd just do it now and save the pain later.

[SP250]

Well done that man.
I do enjoy it when a good solution is found for little or no cash.

[Pete.]

Thanks, I was also quite pleased at not having to buy a gearbox

One thing I noticed whilst working on it - this bike I got at 39k miles was fitted with a recon gearbox from motorworks. It's not on 103k miles so I've done 64k on it, all hard miles in heavy town rush-hour traffic stop-starts, traffic lights, throttle, brakes all the time.

64k miles of that and the gears look like new, the splines also still look like the day they were made. Impressive.

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gears.jpg (191.68 KiB) Viewed 4059 times