GT380B 5th gear noise

Need some help? Put your question up here. Many years of experience on the board to help you get up and running.

Moderators: oldjapanesebikes, H2RICK, diamondj, Suzsmokeyallan

Post Reply
RC36
Still in the Driveway
Posts: 7
Joined: Sun May 15, 2011 8:47 am

GT380B 5th gear noise

Post by RC36 »

A couple of years ago I posted a question in the general 2-st forum about an issue I was having with my 1977 GT380
Here it is again:
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.
As an update that might be of interest to forum members...

I obtained a parts bike-another GT380B- and pulled the transmission with the intent of swapping out the one with the noise issue. When I looked at the gears I noticed a couple of interesting things. First, the 5th drive gear was a different color than all the other gears. Seems there are some that have a brown cast to them, and some are what I would consider the normal gray steel. And then there was the 5th drive gear, that had a color that looked to me like someone had applied significant heat to the steel. Darker, with a bit of a bluish tint. Second, the 5th drive gear has noticeable edge wear. Hard to describe, so I've attached a few photos. Interestingly, there is no apparent wear on the 5th driven gear.


5th drive gear on left, 5th driven on right
Image

5th drive gear

Image

5th drive gear coloration

Image

I've concluded that the 5th gear in the restored bike probably has the same issues as the 5th gear in the potential replacement transmission (pics shown here). So I'm not going to tear into it.

I've also noticed that all drive and driven gears for this transmission are available NOS from various sources - except the 5th drive gear.

Also, the 5th gear part numbers changed with the M (1975) model, so there must have been some issues that needed to be addressed. This seems to coincide with the issuance of Suzuki Service Bulletin GT-10 from May, 1975 that contained a method of increasing the transmission oil capacity from 1.4 to 1.5 liters to "effectively increase the durability of the GT380 drive gear". Hmmm.

So this leaves me with no real solutions to the noisy gear. I suppose figuring out what is going on gives me a little assurance that the tranny is not likely to cannon itself. However, my shift pattern will likely remain 1-2-3-4--6. Kind of a bummer, since the bike runs so well otherwise. And I've increased the rear sprocket by a couple of teeth so I don't absolutely need 5th gear. But it would be nice to have.

I'm surprised that this problem isn't reported more widely and I am looking for any advice, suggestions, commiseration on this.

Paul
Craig380
Expert racer
Posts: 1250
Joined: Mon Dec 01, 2008 2:52 am
Location: Manchester, UK

Re: GT380B 5th gear noise

Post by Craig380 »

Interesting findings ... my own experience is the 380 gearbox is a strong unit.

When I got my 380M back in '98, it had 28,000 miles on the clock, and I was always a bit concerned that 6th gear was excessively noisy compared with the other gears. So I changed the gearbox oil pretty quickly, and continued to change it every 2,000 miles afterwards. The noise never got any better, or worse.

When I sold the bike after 17 years and 25,000 miles, the gearbox was exactly the same as it was when I got it - and I used to ride it pretty hard, I certainly never babied it.
1976 GT380 - wounded by me, and sold on
2006 SV650S - killed by a patch of diesel and a kerb in Feb 2019
2017 SV650 AL7 - naked and unashamed
MarkH
On the street
Posts: 23
Joined: Mon Aug 10, 2015 8:43 am
Country: US
Suzuki 2-Strokes: 75 Suzuki GT250, 74 Kawasaki H2

Re: GT380B 5th gear noise

Post by MarkH »

Paul, thanks for the post!

I am experiencing exactly the same thing with my 75 GT250. My 5th gear is noisy, just like you described. When I did my restore, the bike only had 3400 miles on it, so I really didn't inspect the tranny too much (I just did the crank, bearings (including tranny), and seals). I'm not 100% sure if, once I got it on the road, it sounded like this - I was listening for unusual things, but it never got my attention. Somewhere along the line I heard it...and it bothers me to no end...now I can't unhear it. It almost sounds like a rough bearing or something like that - but only in 5th gear. It doesn't seem to have gotten worse since I starting hearing it (I guess that's good).

Please keep us updated if you find the cause.
http://www.machinesofman.com

75 Suzuki GT250, 74 Kawasaki H2 750, 82 Suzuki RM 125, 00 Kawasaki KX 250, 15 Honda CB1000R
Post Reply