Gearbox issues - shift forks?

[Chuck78]

I've been having some difficulty downshifting for a while now on my 750 8v.
Mind you, this particular bottom end has done great to tolerate an extreme amount of abuse dished out by myself & my thirst for adrenaline and more power (it's seen stock bore pods & pipe, 844cc upgrade, & 920cc top end, smoothbore carbs, etc...)

I ride twisty roads rather aggressively in the hills and mountains, with a lot of aggressive shifting and engine braking.

I suspect I've destroyed multiple shift forks now.
Occasionally I'd experience difficulty downshifting, especially if I'd come to a stop in 4th or 5th gear, and then try to downshift to 1st.

I just rode through the eastern mountains of WV/VA/E. TN/W. NC for a week from Ohio to Alabama for Barber Vintage Motorcycle Festival. I noticed some unusual noise and vibration taking off in each gear from lower rpm the day before arriving. It would come and go, but more prominent when hot after hard riding.

On the trip back home, by Kentucky, it became extremely difficult to downshift UNLESS I kept the RPM's high, 4000+, then it'd downshift fine. If I needed to slow down & didn't have the revs up, or forgot, I'd end up working the clutch to start from a stop in short bumps in 4th or 5th gear until I could lug it...


Anyone ever experience similar?

If I recall from the last time I split GS cases, the shift forks can be removed after pulling the clutch cover & clutch + oil pan.
It doesn't pop out of gear surprisingly, so I am assuming the shift dogs are not terribly trashed. The gearbox shafts I'm pretty certain require splitting the cases in order to remove them. The shift forks I believe can be swapped without splitting the cases, maybe with engine in frame still. Shift drum, I'm guessing may be held captive by the cases. It's been several years since I've had one apart for a major overhaul.

Any words of wisdom?
I plan to fully inspect the clutch components as well, as they haven't been 100% eliminated yet as potential contribution to these issues.

Thanks!

Chuck

 

[GregT]

I'd be more likely to suspect worn clutch components giving excessive endfloat. I've seen this cause shifting problems.
Easy enough to pull the clutch cover and start pulling and pushing on the clutch basket to see how much endfloat there is.
It's possible - though unlikely - the rails the forks ruin on may be bent. If it isn't jumping out of gear this is less likely.

 

[Carter Turk]

Maybe the tangs on the clutch fiber plates have left pronounced dents in the clutch basket.

 

[Buffalo Bill]

I beat on my 1100G trans when I'm pushing over 7000rpm. It's just not very refined compared to the next generation: SACS oil cooled.
Forgetting to down shift before stopping always results in a small jam. Usually because I missed a turn and stopped suddenly.
I just shift down one, let the clutch out a bit, then down shift again til I get to neutral. Then carry on with the ride.

 

[Chuck78]

When I forgot to downshift at higher RPM as I was slowing down to 40 mph to turn into a gas station, I showed up at the pump in 4th gear and it took me about 4 minutes to get it back into neutral... That was pretty frustrating! At least I can slip the clutch and pump it in and out a bit to get going from a stop in 4th!
The clutch action seems pretty smooth so I hadn't considered that the basket was severely notched.
Unfortunately it's not looking like I'll get to ride it anymore this year as I have too many projects in the next few weeks and I make Halloween the cut off due to deer season and not liking cold temperatures. Especially after hitting a deer on the GS750 in 2012 on November 12th!

Hopefully I can make it a productive winter project season, hoping to heat the garage this year, and I can take bikes down into the basement workshop of my house now...
GS400 489cc build, perhaps GS1000 rebuild or Rickman CR1000 frame powered by a big bore stroker GS1000...
The 750 hopefully will not require pulling the engine, as I have a lot of bigger projects I want to tackle.

 

[Chuck78]

2022 riding season update - turns out my suspected shift fork / gearbox issue was entirely caused by excessive hot swelling of the clutch friction materials... I dusted the bike off and pulled it out to prep for a 10 day road trip that I usually open my riding seasons with (May birthday road trip), and it seemingly shifted fine cold and parked... I had horrific memories of pulling into a gas station or up to stop lights and forgetting that I'd needed to downshift while at 4500rpm or higher, and being unable to downshift without accelerating first. Even stopped and after filling up with gas, I couldn't even get it to shift into neutral or any gear hardly, until excessive attempts. Shifts pretty alright sitting now.
I had recalled in the past several road trips, that the clutch cable freeplay had started becoming excessively loose after riding for a bit, like half a lever of pull before the slack was taken up. I'd start out with a perfectly adjusted clutch, and then have to adjust multiple times on the fly while riding in order to get proper clutch feel, or as best as I could get it.
Apparently the standard grade EBC clutch discs are somewhat well known for hot clutch swell, causing these issues, but mine was an extreme case as the clutches would not let go enough to allow proper downshifting. I might have hosed some of the shift dogs or forks a bit in the process while fighting with the clutch swell issue and stomping the pedal every way possible trying to get home from Barber Motorsports Park in Alabama (Barber Vintage Festival) to Ohio... it was mostly on the last legs of the return trip riding 10 hours home in which I experienced this complete inability to downshift.

I'm not sure if EBC offers more performance oriented options for the GS750/550/GT750 etc discs, but my wife, who works in powersport parts sales, is telling me that they do have several different grades of clutches, & the CK is the just basic cork type friction material. I'll stick a 40 year old OEM set in for now and look into the upgraded friction discs later I suppose, now that I'm departing in 5 days for a 10 day haul through the Eastern mountains, with a kickoff meeting up with a small crew of veteran members from the dotheton.com forum from all over the USA who are buddies with one of the semi-local to me guys.

 

[rphillips]

Glad you've got it sorted out. I've never heard of anything like plates swelling enough to cause this kind of problem. Good info to have in the bank. I'd think the 40 yr. old oem. should do fine. Thanks, & Have a great trip.

 

[CincinnatiKid]

Howdy friends!
I've been experiencing this same sort of issue on my 81 GS1100E

For the most part, it shifts okay. Upshifting is rarely an issue, though it's noticeably "vintage" when compared to my KTM.
Downshifting into lower gears is less smooth. I don't use a ton of pressure to shift (or try not to), but instead opt for a repeated gentle press/tap on the shift lever to get it to shift.
especially trying to get into second gear, but sometimes third, and sometimes first, the feedback from the lever feels like it's already in first. like it's trying to shift but there's nowhere to go. a few more taps, and maybe a little clutch in-out, and it will generally get where it needs to go.
The issue is most prominent when trying to downshift two gears when coming to a stop after a spirited rip before a corner, looking for some engine braking.

its more annoying than problematic, but I know there's an issue and it could be better. I can work around it on the street, but i would like to be able to bring the bike back to a track at some point, and I feel it would be mega frustrating at a track day.
I was initially thinking shift forks, but some searching on the forum has me thinking i should do a clutch inspection, as well.

I guess i'm just posting as a record, and seeing if anyone has anything to chime in with. My engine does it independent of heat load, so i don't think its the same as Chuck's issue, but i didnt want to make my own thread for it.

thanks

 

[Nessism]

Changing the clutch friction discs and steel plates with new OEM parts transformed the shifting of my old 1000S. It went from clunky, and difficult to find neutral, to shifting like butter. I have no idea if your bike is same, but just say'n...

 

[Chuck78]

Definitely the first step is to inspect the clutch steel plates for warpage (& wear on the friction material), then check the clutch basket for notching. Barnett racing clutches are thinner steel (in order to allow room for one extra plate+disc) & are notorious for notching the clutch basket, which can also make the clutch action "hang up." Warped steel plates will make it very difficult to find neutral when engine is running especially, sometimes when the engine has cooled off but discs still obviously permanently warped, neutral will suddenly be much easier to find.

Hot clutch swell is absolutely an issue as I've learned particularly from becoming more and more obsessed with 2 stroke trail bikes and riding hard enduro type terrain the past 8 years, particularly the past 3 of really seeking out the challenging tracks...
Hot clutch swell is a normal thing, but some oils and some clutch friction materials will exhibit significantly greater swell as I'd learned 11 months ago.
A normal amount of hot clutch swell combined with slightly warped clutch plates aka "steels" will cause degraded shifting performance and difficulty finding neutral without a doubt.

My issue was so extreme after doing long highway hauls into strong headwinds cruising at 85+mph, that even with the engine off, I felt like I'd not be able to downshift whatsoever.

 

[CincinnatiKid]

right on, all great info, much appreciated.

unsurprisingly, when i did an oil/filter job a few days ago, it really seemed to help mitigate the shifting issue. it's not completely fixed, but it's better than it was!

When i got my first GS750 about 5 years ago, i remember reading that the GS clutch was way overspec'd and would likely outlast most components of the engine. the advice was that if there's an issue (there was), it was likely in the springs, and not the plates themselves. that advice was correct. I have been assuming that the 1100 engine is the same, and have never felt like it needed service. Perhaps it's time for an inspection/overhaul.

that notching, you guys talk of, is that seen as the steel plates wearing into inside faces of the aluminum clutch basket housing?

also, it seems like the opinion is that OEM or OEM equivalent friction and steel plates are the best bet?

 

[bwringer]

Yet more proof that OEM clutch bits are always best.

 

[Chuck78]

Yes I'm definitely going out of my way to buy OEM Suzuki and Kawasaki friction discs for my bikes, might as well get the OEM steels also. I've been running at Shell Rotella T4 and regular Rotella tea before that, for as long as I've had motorcycles, and I've never had the hot clutch swell issues on anything like I did last year when riding from Alabama to Ohio. The bike had been getting increasingly more difficult to shift for a while, but that long ride home in one shot on the highway really did it. I rode for 10 days prior to that but not highway miles, all winding through the eastern mountains from Ohio down to the Cherohala Skyway and vicinity, leaving from tellico River Gorge and doing 3.5 hours direct to the Barber Motorsports Complex. That didn't make it act up anymore than usual, but that Long haul on the highway just booking it to get north south across the country, that definitely was the worst I had ever experienced hot clutch swell. I didn't know that was even possible to that extent until I figured it out when I got my bike out the next spring as I didn't ride it any after that, thinking my transmission was shot.

One thing of note, this Suzuki specification for permissible warpage of the steals is significantly higher than I would expect, I don't have a manual in front of me, but I wouldn't run them if they were halfway from what Suzuki calls out of spec, it just seems too much to me for the issues I've had on certain bikes finding neutral when the engine is running, usually caused by warpage of the steel plates or potentially hot clutch swell.

 

[Chuck78]

And yes, the basket gets grooved from the fingers on the friction discs hammering into the aluminum clutch basket slots. You can very carefully and precisely file them to the bottoms of the notches and get proper operation back, but then they have a little bit more free play back and forth and will eventually hammer themselves more indentations into the basket.
It's best to get another used clutch basket at that point, especially if it's a 16 valve 1100, you can buy billet clutch baskets for those still.

 

[bwringer]

One other anecdote... a few times, I've found GS and KZ engines with problematic shifting caused by Barnett "Extra Plate" clutch kits.

Back in the '80s this was a popular, if inexplicable, modification. Basically, the kit contained a set of thinner plates so you'd end up with an extra plate in the stack and supposedly more friction. Even though the stock clutch was well-proven to hold up to substantial increases in horsepower, this was the hot setup for drag racing or something for a while, never mind that it was hardly ever needed, made the bike a pain to ride, and the thinner plates warped and notched the baskets more easily.

I dunno, we didn't have the internet back then, so stupid word of mouth stuff like this was passed around as if it were gospel between people wearing acid-washed jeans and mullets. So you find random Barnett kits in bikes with no other modifications.

The same rampant misinformation also led to thousands of discarded airbox lids and airboxes, as well as airboxes with holes in them and gutted exhausts, yet information on proper rejetting hardly ever made the jump from mullet to mullet.

Valve clearance checks were also seen as frightening, alien, and completely unnecessary, so quite a few GS Suzukis were rolled into the back of the garage, or propped against Granny's barn at around 12,000 - 15,000 miles, condemned as "worn out junk" because the valve clearances had finally become too tight for the bike to start before the battery gave out for the last time.

Anyway, yeah, watch for that. Count the plates. The Barnett plates are a weird coppery color, not that sort of greenish/brownish/black of stock plates.

Monkeying with clutches was weirdly popular; I've found damaged clutch baskets on low mileage bikes several times, more than once with 1/4" bolts jammed in there rendering the whole basket and hub an unsalvageable mess. I can't explain why.

 

[Chuck78]

Yes I forgot to mention the Barnett clutches although I might have mentioned them previously. As Brian mentioned, they are all thinner in order to fit one additional friction disc and steel plate in the same height.
Barnett clutches are easily identified if I am recalling correctly, from the friction disc backing plate not being thick aluminum like the stock or EBC friction discs, but instead I believe they were steel, and I recall the ends pretty clearly being folded back over on themselves as if they were twice as long and then the end finger parts that insert into the clutch basket to engage, they were folded 180? over on themselves. Thinner material area to contact the basket and also a harder material, both of which would lead to a badly notched grooved basket.

 

[CincinnatiKid]

Amazing

i love this forum