GPZ Gearbox - on the way out?

[mchaggis]

GPZ500, 1989, 27.5k miles, oil and filter in need of changing.

Something the other day finally confirmed the problem for me. Every time I throttle on (in any gear) there is a jerk as the power comes in. When I close the throttle from high rpm, every so often there is a funny jerk in the delivery.

The clincher was yesterday, throttling off in 3rd from a quick squirt up a short section of dual carriageway before it turns into a 40 with a speed camera. All of a sudden, I'm in second and the engine's revving it's nuts off as you might expect. It has happened to me before too, where I've just changed down a gear and the bike's changed down another, going from 5th to 3rd at 70.

Basically, gearbox lash + dropping down gears when throttling off from high rpm = gearbox gubbed? But what and how? It never drops out of gears under high acceleration. I'm confused to say the least.
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I must not be a troll...
Mmmm, Guinness
Discovering the delights of Hammerite and a 3/4" brush.

[Kickstart]

Hi

Under load the dogs (if undercut) will be less likely to let go. If not undercut then the load will help it pop out of gear. No idea on the GPZ box (but given it is a fairly pleasant gear change I suspect it isn't undercut). Normally would just dump you into a false neutral though on most bikes.

However I cannot see a likely way for the box to go down 2 gears at once.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[mchaggis]

As far as I know, it's only actually changed down 1 gear at once, but I'd only just changed down myself, hence the buttock clenching moments.
____________________
I must not be a troll...
Mmmm, Guinness
Discovering the delights of Hammerite and a 3/4" brush.

[Kickstart]

Hi

Not sure how it could, although possibly very worn selector forks might allow it to happen (but I would expect these to have caused loads of problems before getting to that stage).

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Paddy Blake]

[davidimurray]

May sound stupid - but have you checked the state of your chain and sprockets?

[mchaggis]

[stinkwheel]

They can develop a LOT of play on the cush drive too. Give it a check (by trying to rotate it one way then the other). Shim it out with strips of inner tube if necessary (dinnae bother buying new rubbers, they have play in them from new).