Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board Gearbox Issue

I've had my 66 TR6 since 2006, when I got it gear changes were hit and miss to say the least. I opened up the box and found one of the selector rollers laying in the bottom of the box, the previous owner said it must have been like that since 87 when he last put it together. Refitted the roller and the box was much improved, however when opening it up in second it would just touch 5000 rpm and jump out of gear leaving me stirring the box for anything I could find. All the rest of the gears were fine. Recently I got around to replacing the selector forks and finally cured the problem with second gear. Now if I don't hold upward pressure on the lever it will jump out of 4th gear. Any thoughts?

You know the answer, open it up......... there's no easy way. LOL.
May be one of the bearings, dogs, plunger etc etc. even the nut on the end of the mainshaft.

I'm not saying this is the cure but removing the detent plunger and making sure its clean and not sticking/worn and then adding a 1/8" spacer under the spring to give it more pressure normally helps.

What did the shifting fork peg and the camplate groove look like after 33 years of the peg moving the camplate?

When a gearbox is jumping out of gear I always ask myself whether I'm sure the box ever gets fully into the gear that's jumping out.

I'm posting two images to help visualize the problem:

The shifting mechanism:




The position of the camplate and the inner quadrant when the gearbox is in 4th gear:

Nick, yeah I know! However since this bike has gone back to being my daily transport I figured it wouldn't hurt to ask just in case someone has been here, then I could have hopefully had it apart, fixed and ready for work in the morning.

I have replaced the detent plunger spring along with the springs in the outer cover. Couldn't hurt to drop a ball bearing in the plunger housing I guess.

Hermit. The selector forks had damage on the ends of the selector rod bores but the pins themselves didn't look too bad. When held against the new replacements you could however see they were bent, I'll dig them out and snap a pic. The cam plate looks in good shape, no obvious burr's or damage. Thing is this is a new fault, it never jumped out of fourth before so I have been thinking about what I did different. The only thing that springs to mind is that I omitted the locking washer on the main shafting in favour of Loctite. I'm wandering if this has effected the end float on the shaft. It's a starting point.

The lock washer shouldn't matter, but if the thrust washer between the sleeve and the bearing is misssing, then it may. That thrust washer was not used on the pre-unit boxes, they had a slightly longer sleeve. I never have figured why the washer was added, I can't see why the spring acting directly against the bearing inner was a problem!
Good luck on this one, keep us posted,
Mick.

On the pre-units the sleeve butted against the bearing inner radius which provides little surface to support the clamping force from the nut. That's the reasoning behind the thrust washer, only it's to soft to be really effective. On most gearboxes I work on the nut will be loose due to that. In my experience one of the things they never really got sorted. No biggie though, I use Loctite on the nut and torque it to 25-30 lbs-foot. I never bother with the lock washer, It's a waste of time.

On the problem at hand, the 4 speed box relies on the camplate plunger to keep the gears engaged, and the dogs are straight cut. Faults to look out for are worn engagement dogs, worn cam-tracks, worn rollers, worn shift forks, a weak plunger spring, and so on. In a word: look for wear.
Worn and tapered engagement dogs will exert axial forces on the shifter forks that can overcome the plunger spring. It's a very real problem on many high mileage machines, and replacing parts is the only real option for most of us.

SR

Ah, yes, I can see that with the radius. I haven't got a 4 speeder apart at the moment, but there are definitely two different sleeve lengths depending on whether the thrust washer is fitted or not. With no thrust washer and lockwasher and the shorter sleeve, the nut MAY not clamp the mainshaft properly, I suspect that you could only check this on an assembled box. Obviously you are right about wear etc, but if the problem was not there before, it could still be something silly like the roller dropped off the selector fork.

The mainshaft has nothing to do with the box jumping out of 4th. It is going to be the fork, fork roller, cam plate track and the indexing of the camplate that determines the position of 4th engagement. If it didn't jump out of 4th before, there is a very good chance the camplate isn't indexed correctly. Personally I wouldn't ride it until sorted. Clean threads, free from any oil, and Blue Loctite works on that nut.

Thank you, John. I hadn’t really considered the indexing, I always use the method in the manual. Can I assume you are thinking I could be a tooth out on the back of the cam plate?