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GS750B won't downshift when hot. Oil, springs, swell, shift forks?

Chuck78

Forum Sage
Past Site Supporter
I've had this problem once before in recent years on long yaul road trips. Replaced the still-in-spec EBC clutch friction discs with some original OEM well used discs, didn't experience it again.

Fast forward 2 - 3 years, haven't done anything but 200-400 mile twisty road rides in that time due to family medical issues and spending most of my free weekends on 2-stroke dirtbikes.

Now after 600 miles on the interstate yesterday Ohio>Kansas City, the last 250 miles, I can't downshift when stopping for fuel... 4th is no problem, 3-2-1 are a NO-GO for about 6-20 minutes until bike cools off.


I suspected maybe the rumor "Rotella changed their formula a few years ago and although Jaso MA rated wet clutch safe, it's not acceptable" could be true, but also I had suspicions this rumor started as Rekluse used to highly recommend Rotella T4, UNTIL they started selling their own brand oil, and now they say Rotella is no longer good. Rotella in bikes is a very controversial and polarized topic these days. I've been running Rotella in EVERYTHING, including our diesels, 2-stroke dirtbikes, and GS's, no other issues except the "iron butt long haul = can't downshift until cooled off."


Any thoughts?





​​​​​​I can pull in the clutch lever and idle, so the clutch not so swollen up and stuck that it would kill the engine or make the bike creep forward, but I'm wondering if it's enough pressure from lack of fully disengaging that it's not allowing the shift dogs to move amongst themselves to align properly?



I'm also wondering if the clutches are slipping slightly perhaps due to worn weak springs, which is causing swelling? Or if the engine is running hotter on these long interstate passes and breaking down the oil viscosity more, which is causing issues with worn shift forks in the drum? Make sense why fifth and 4th work better, I absolutely hammer this thing in the twisty roads at high RPMs nonstop, that's my primary interest with riding street bikes. Perhaps a more slippery motorcycle -specific oil that promotes better smoother shifting might help the issue?



At any rate, I suspected if I change the clutch plates and discs, clutch springs, and oil, this issue may go away, unless there is some issue related to the shift forks and shift drum when hot. I don't have a center stand to put it up on to see if the wheel spins with a clutch fully disengaged lever pulled all the way in while running. 700 more miles to go today, probably the last 100 or 200 tomorrow. It would be a shame to get to the Rocky Mountains only to hitch a ride with friends to our white water rafting destination, but I'm afraid of the inability to downshift when riding mountain roads...


I'll try giving mechanical clutch adjustment (at the engine case) a bit more free play before I leave the hotel this morning, but since I can pull in the clutch when stuck in fourth gear and sit at a stop without the brake on, I'm not sure that will fix it. It's interesting that this only happens after extremely long highway runs. I should also note that I went from an EBC 112.5 Main jet down to a generic 110 (I failed to heed my own advice as to not mix brands of jets and trust the sizing across brands...) as I was just a slight bit too rich, and now I'm way too lean on the mains avoiding over half throttle until I get to Kansas City where hopefully I can buy some EBC jets or Mikuni jets, so the engine is definitely running a bit warmer. I'm running on 93 octane now for this trip due to that. Spent most of the 10 days prior to leaving working on my wife's '88 BMW R100GS and was rushing with mine and figured one jet size down didn't need testing the night before in the rain at 11:00 p.m.!
 
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My issues where based on - shifting issues up or down - neutral hard to find or not at all without killing the engine - which caused issues adjusting the cable for proper free play.

With my '77 750B ( both my '77 GS750 and '78 GS1000 engines in my 750 frame ) when I have the issue you're fighting, I've always replaced my friction plates.
I even went through and cleaned up the divets in the basket prior to replacing the plates hoping it would help. Clutch felt smoother but plates were still sticking.
You might try opening it up and moving the frictions around and change your oil.

I run VR1 20W50 oil but I live in Florida...

I have a dead "77 750 engine with brand new EBC plates and good steels - engine took a dump - that have about 100 miles on them - as well as a rebuilt clutch cover with new actuator, rubbers, guides and SS allen screws - I would be interested in selling the whole baskets assy if interested. Clutch worked flawless before engine failure and I've pulled the pressure plate off to prevent the plates from sticking.
If you're still in KC, I have family there.
 
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This may be a different issue, as it still persists after engine is shut off. I've noticed that most issues with finding neutral when running (but not a problem as soon as engine is off) are notched basket or warped clutch plates etc.

This really requires the engine to cool off for a while to resolve.

We just rode 50 minutes at 75+mph, and it shifted totally fine!!! Except that I believe I've now slightly bent my shift shaft from stomping on it so much when the problem acts up like last night.

On way to an old timer's motorcycle shop to buy some Mikuni jets, I'll pick his brain...

600 more miles to the Rockies!
 
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