Clunky gearbox

[tfb]

G'day all,

My GS1000ST (1980) is a nice old beastie but...

... the gearbox isn't that slick or smooth when it comes to gear changes. Up or down, it usually slots into gear with a loud 'clunk'. If I'm reaaaaaaally careful I can minimise it. But it's still a pain.

Otherwise the gearbox is fine, with no slipping out of 2nd gear or any other such typical problems that you get with older bikes.

My first GS1000S that I had about 15 years ago (a 1979 SN) had a much smoother gearbox. And my current GS(X)1100SZ Katana has a very slick unit too. Just a quick snick with the toe and it's in with no fuss or bother.

The drive chain is in reasonable condition (no tight spots) and is correctly tensioned. I recently fixed the rattling springs in the clutch basket, and that only marginally improved the clunking gearbox issue.

So, any takers for what the cause of the problem might be? (And pleeeeeease, don't let anyone say that "they're all like this, sir" because I know for a fact that they aren't!)

Cheers,
Mike.

[hampshirehog]

Mike - you're right, they ain't all like that. In my personal opinion Suzuki made the best boxes at that time and my S changes gear as smooth as a baby's bottom.
I presume the clutch is correctly adjusted.
If you're lucky, it might be a bit of muck in the gearbox. Have you tried changing the oil and flushing through? If that doesn't work first thing I'd look at is the return spring on the dog behind the clutch - check that it re-centres spot on every time you shift the gear lever. have a look at the pawls and springs while you're in there - they can pick up bits of muck and stick a bit. Almost forgot, another place that accumulates muck is the stopper cam underneath.

After that you're into a gearbox split. Bent selector forks are a possibility, especially if the PO was a bit of a brute - or worn shaft if it's a high mileage bike. If the motor has been split in the past my money would be on the stopper cam being slightly bent - they are about as unbendable as custard and easily damaged.

[hampshirehog]

Another thought I've just had. On the mid to late 70's (might have even been 1980) TS250 Suzuki changed the stopper cam design. Or rather they didn't - it had a new part number but looked and measured the same as the previous part yet it was different. The dealer where I worked sold a few TS250s with clunky boxes and had to do a recall to swap the stopper cam over - the factory had used the old part in error. It was a right beggar if you got the new one mixed up in your hand with the old one as we couldn't tell the difference. Anyway, this always cured the problem, but always struck me as odd as I swear the parts were the same.

I've had a look on the online parts fische and the part no for a 79 SN is the same for an 80ST, though for the TS the part no change was a lot earlier than I recall (73 /74 - I was still in shorts then) so there could be an error in the fische. And did the factory make the same mistake twice?

[tfb]

Excellent pointers there, gentlemen! I had been thinking about bent selector forks, and that's always a possibility, but the fact that it is so easy to change gears makes me think that may not be the problem. It's just the almightly "clunk" when the gear change is performed; otherwise it's all as easy as pie.

Sump is as clean as a whistle (among the first things I did when I got the bike was clean the oil pick-up screen), the oil is fully synthetic 10W40 changed every 3,000-5,000 kms.

Now then, the stopper cam, hmm? It would never have occurred to me... but as it's so accessible guess what the first thing is that I'll be looking at!

Cheers again gents, I'll keep you posted.

[Guest]

Is your clutch basket tight? If yes I'd go with the bent shifter forks or worn drum. If it doesn't slip out of gear when beating the crap out of it the dogs are probably good.

[tfb]

Thanks for asking chef1366, yes the clutch basket is indeed tight (I know because I did this not that long ago when I rebuilt the clutch basket).

Of course I'm hoping the problem is more accessible than the internals of the transmission. So I'll check out the pawls and all that first and take it from there.

Here's hoping I don't have to split the cases!

Cheers,
Mike.