GT380 5th Gear Noise

[RC36]

Two years ago I resurrected a 380 B that had been sitting in the neighbor's garage for over 30 years. Less than 10,000 miles. Runs like a dream now...except that I have a noisy 5th gear. It could be described as a 'whirring' - sounds like there are a whole bunch of extra gears turning is the only way I can describe it. And it is more than a subtle noise.

No problem shifting in/out of any gear. No noise in any other gears. At first I went "what the heck" and kept my hand over the clutch lever. Now I just go 4th to 6th to effect silent running. But it is like trying to keep your tongue off a chip in your tooth-have to run it in 5th just to see what happens. Nothing HAS happened but I'm wondering if this is just a character of these bikes. But since a search of this site does not yield anything, perhaps not.

Part of the rehab was to replace the shifting fork shaft, which was bent, presumably due to a mishap by some previous owner. That seems to be the only thing related to the transmission that might be involved, although I cannot see how.

I have a parts bike sitting out back, but with my limited experience with servicing transmissions I'm not sure that even if I had two transmissions sitting side by side I'm not sure I would be able to tell what was screwy, unless there were pieces missing/broken/loose metal, etc. And then there is the fun of pulling two motors, splitting cases, etc.

Any thoughts would help.
Thanks,
Paul

[yeadon_m]

Paul,

It should not make a noise in 5th that isn't in keeping with 4th and 6th. I suspect the 5th gear drive or driven (or both) are worn. Unlikely to be a bearing and, I would have thought, a selector fault might make gear selection harder but not noisier once in gear. My GT380B is a little noisy of gearbox, I think final drive shaft bearings, but in my case I have to try to hear it once helmeted and its loudest when I can it hear the least, like 70mph and up

All my GTs make slightly different noises in each gear, but not markedly so. Its a mechanical system.

Cheers,
Mike

[Craig380]

It's really hard to advise exactly on noises ... what one person thinks is excessive, another would dismiss as nothing to worry about, and vice-versa!

When I got my 380 in '98, I was concerned after my first couple of rides on the bike as I felt 6th gear was noisy, making a very noticeable 'whirring' noise compared to 4th and 5th (which were and still are very quiet).

I changed the gear oil for the right amount of fresh 10W40 4-stroke bike oil, and the noise in 6th got a little bit quieter, but was still there. I decided to leave it for a while, and see if it got any worse. 16 years and 25,000 miles later, I'm still waiting for it to get worse It's never changed. So I've never split the cases.

I change the gear oil every couple of years (about 4,000 miles or so) and there's never any evidence of metal in it, nor was there any evidence when I replaced the clutch friction plates a few years back.

[RC36]

Thanks for the comments. I conclude from the comments (or lack of them) that there is no particular common flaw in the GT380 tranny that would cause the noise. I woke up the other morning thinking about this issue and recalled my initial attempt to free up the stuck pistons on this bike when I started the rehabilitation. Finally had to fabricate a puller to get the cylinders off the pistons, but before that one of the things I tried was putting the bike in gear and rocking back and forth. The bike may have been in 5th??? I didn't think I was excessive with this maneuver but it is the only thing I can think of, other than abuse by the previous owner or factory defect. Could this have caused significant wear in the drive/driven gears?