GasGas Shift Spline - Fatigued Teeth

I had a great time at the 2-day trial June 2015, Sipapu, NM.

Saturday was hard on me. I lost "my quiet mind" on Saturday, but got it back on Sunday. The bike, however, always performed awesome!

During bike check-out on Friday, however, I had an unpleasant surprise.

I found it puzzling that over the previous month I kept having to tighten my shift lever every now and then. Just before going up to Sipapu, I relieved the gap with a hack saw and tightened the crap out of the 5mm screw. Friday, after some riding, it was loose again! So I removed the shift lever to put on my spare, thinking the problem was wallowed-out splines on the forged aluminum shifter. To my surprise, I found half my hardened steel shift shaft splines had broken off, mostly toward the outside and rear-facing side. The splines came off in pieces, like little needle bearings.

This was a fatigue failure at the base of the teeth, due either to over hardening the shaft, or perhaps being whacked hard some time in the past? I'm gentle on shifters, so it wasn't how I was shifting.

I wonder, is this a known failure?
My bike is an `11 (pre `12) and thus has the older shift shaft setup that requires splitting the cases to fit a new shaft

I had two days of events to ride, so I knew I had to do something temporary. I went begging for JB Weld, which is an epoxy with metal powder. I found some first person I asked!

I cleaned off the shift shaft and shifter really well with some brake cleaner and paper towel. Then I mixed up some JB Weld, and coated with shift shaft and the shift lever bore. I then put the shifter on with two bits of stainless steel wire (0.025") in the gap where the teeth had broken off on the back side. All went together well. I tightened the screw, and let it cure over night.

Not only did the repair last both days of Expert banging about, but it looks like it's strong enough to last the rest of this riding season:



I plan to hold off on replacement until this coming winter, but I'll buy the part now.

Good ol JB weld. Right up there with duct tape and zip ties in my book.

+1

Some of the best stuff you can use in a pinch.

The shifters always loosen up, but the first shift shaft I have heard of the splines failing. I had a spare with me, we could of split it at Bruces`

GasGas should include a tube of JB weld in the fanny pack with every new bike.

What's the rubber, zip tie, and wire around the screws holding the plastic chain guide for?

Bene, post a bigger picture of your custom left hand brake.

Aha! You noticed! It's simply a way to hold a rubber strip that spans the open gap between the chain protector and the front sprocket. That's a drop zone for mud and grit from the wheel turning. The rubber keeps some of the dirt off the chain, so it will last longer.

Here's a view of the shift shaft from inside, and why changing one of these out requires splitting the cases. Very interesting how the shift shaft is the center shaft for the shift drum! More of that design integration this engine is famous and sometimes criticized for.

Here you can see the shift shaft teeth all nice and fresh on the Econo's engine.

Okie doke. I don't do left-side brakes on dualsport or road bikes. I can heel the right-side brake in those cases.

I've had to do one of these on every trials bike I've owned since 1987. My TY Yamahas had a rear-facing left-side brake lever mounted to an aluminum bracket (sorry, no pix). My three Fantics, Two Shercos, one Scorpa, and two Gassers have all had custom setups.

Lots of hours in the machine and welding shop go into each one. That's one reason I tend to stick with a bike a long time. A new bike every year would be too much work! My goal is they work first time, strongly, and keep working reliably. That means hours up front.

Required is a custom brake lever and a way to pivot it on the left side, either by welding a pivot on the frame or mounting a machined piece and bolting it to the frame. Then there's mounting the master cylinder on the left side.

I favor the older style remote reservoir master cylinders because I don't have space taken up by the puffed-out integrated reservoir. A custom brake line and reservoir line typically are zip tied together and run around the carburetor air boot.

Here are some pix of the general setup:

I start with brake lever I made from a prosthetic foot stainless steel shoe horn and other bits:



Then I need a pivot on the frame. This one I machined from a bolt. It's in position, pre welding:



Here's an older version of a lever and pivot, on my Fantic. The lever is stainless steel and the bushing is simply a welded into the frame:



Here is my old Sherco setup. Al machined aluminum bracket screwed to the frame with two 6mm threads in the frame:



Another view:



The toughest part is where to put the master cylinder. It gets tight on the left side with carburetor and chain there. I've always found a way. It just takes a lot of careful hours to make something that works first time and keeps working. My current GasGas with round-tube frame a challenge. Here it is during fabrication, and before I painted the black frame red:



The previous Econo with elliptical-tube frame and older style subframe was great because I could put the master cylinder inside the subframe. It was tight at the airbox boot, however:



Another challenge is the brake line. It has to snake around the air boot. I figure it out then have Speigler make me a custom line. Here is the Econo example:





What will my next bike be? If GasGas goes poof, probably either a Sherco or a Beta. I like both. The Beta would be a serious challenge! It is the only bike with the older European right-side chain drive. The Beta has a lot of stuff already on the left, shift lever, kick start (which would swing through the general area a left-side brake would occupies), muffler... Not much room to add one more function.

Ok, my question is why? Are you missing your right leg? We've got a one legged off road racer around here that's missing a leg and run's his rear brake with and extra lever on the bars.

http://advrider.com/forums/showpost.php?p=25005584&postcount=1379

Makes sense now.

Quentin has raced around here for so long now, it just seems normal. He doesn't wear a prosthetic and kickstarts his bike and picks it up and drags it out of mud holes like everyone else. And you better be riding fast, or he's gonna pass you. He left it behind in Vietnam.

Missing right lower leg only (just a scratch - as they say). Can't pivot my ankle when standing on the pegs, so given braking is so immediate and critical in trials, and shifting and braking there are in separate spaces, I put the brake on the left foot.

When cross-country racing in the `80s, I tried several hand setups, but they were not effective, so I learned to just heel the standard brake on faster bikes. Kinda scary to miss the lever flying in to a corner!

I've had people point out I should use a Rekluse clutch and put the rear brake on the left hand. That would work well if I had a KTM 500 or such, but my offroad bike is a KLX330 dualsport that needs at times a great clutch to make up for less beans. As a trials rider, abandoning advanced clutch techniques to not heel the rear brake has not been a trade-off I have been willing to make. I have a KLR685 a Rekluse clutch might work well on, but again, the standard foot brake isn't a problem for me.

I found the Yamaha TY left-side brake in a dusty box. I'll seek to post a photo of that too. It's an odd one!

Bene, is there a chance these are slightly tapered? I too have had the issue, I have spent the last year where I make sure the lever is tight before the event, and yet I actually lost my lever, at least once in several events, having to go find it on the TRAIL or last section I shifted the bike. I even lost it 5 minutes after hastily tightening it once, which can blow your quite mind, if you know what I mean...

TO me this has be raring its ugly head, since adding flywheel weight. Before the FWW, I don't recall ever having a loose shifter lever.

I too have done everything you have done to the lever, my next step with it will be a BOLT that is longer and a nut? I broke my OEM shifter, ended up with a S3 model... what I thought was happening, is stretching... But I am NOT some engineer, I cant tell if my shifter is NOT slowly stretching. I have a bet, that I am slowly stretching the lever clamping surface around the shaft? maybe a dab of that glue you used is a good idea? and not having to tighten as much?

I have NOT inspected my splines as such, but expect same thing.

I know we fixed kicker's that used to strip splines on the old Montessa's and other bikes, using a tiny drill bit then using a nail or 3, as a "key" like the key on a flywheel has. might save you buying new shaft, but that is just a thought. Might need to get the shaft now, before we CANT get them? :eek1

Buying a shaft is no big deal. The pro (at least the earlier models) require the cases split. That is quite a waste of a day. All other bikes it is a 45 minute job. By the way, I`ve lost several shifters on a Pro. That`s why there is one in my fanny pack and another in my parts box.

I have been lucky, broke one, replaced and dropped that SOB 50+ times... but found IT... luckily it is RED easier to spot most of the time.

The splines are not supposed to be tapered... saying this from the knowledge of the manufacturing process for splines.

GasGas did not use the method of a groove in the shift shaft where the shift lever screw locks in so it can't fall off it gets loose. That's a good thing for us, because the forged aluminum shift lever is unfortunately a tad short after adding the flywheel weight and cover spacer, and we are not locked into one place but can slide it out a tad.

I had mine come loose a bunch of times and I eventually ended up pushing it on as far as I could, but by then my splines started breaking off. Stoodley told me a couple of days ago that he has seen some shift spline teeth failing in 2011 models, and mine is a 2011. Maybe a lot of over-hard shafts? Stoodley's temp fix was like yours: drill at shaft-shifter intersect and insert a pin to take the torque of shifting.

I have taken to safety wiring on my shifter... front of shift to up near the front engine mount bolt, just so I don't lose it if it comes off. Not that it will anymore, being JB Welded on!

Hey, I have JB welded a couple things in my life, never needed to take them apart, if it failed had replacement, you know... like cases or something that holds liquids... How much of Beyotch is it going to be to get the lever off now that you JB'd it? Just a dab? or what did you do?

Just curious.

Noticed mine was loose today and was wondering the same thing