Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board upgrading a 1972 five speed gearbox

way back when i was just legally able to buy beer, i bought a 1972 triumph bonneville, used, for $600. i couldn't afford the brand-new 1977 T140s they had on the floor at triumph of oklahoma city, and the nortons over at cal's motorcycles were also out of reach. i still have that bike, and it still has the awful leaf-spring indexing mechanism, and the fragile early five-speed gear set. lately it's been getting hard to shift, and i'm getting more and more leery of the driving dog that locks into the layshaft first gear when you select first from neutral. it's already blown apart once, at a stop, and i'd like to avoid a repeat with more serious consequences.

i've got it up on the lift, and i'm going to drill it out for a camp[late plunger assembly, and i'm also going to pull the whole gearset--all of it-- and replace it with a later assembly i bought here on the forum.

disassembly first. this bike was flooded about 12 years ago, and the muddy water filled the motor through the carburetors, and the gearbox through the clutch cable entrance. i drained it out and got it running, and it's been fine ever since. but the gearbox has been progressively stiffer. here's what we're starting with:



first thing, was to get it on the lift and drain all the oil from the OIF oil tank and the gearbox:



when i pulled the outer cover the oil inside didn't look so hot.




it drained out clean and clear, but there was a bunch of sludge in it, nonetheless. i confess i haven't had it apart since i rinsed out the flood water, and maybe i should have rinsed it more than the two or three times i did. more rust than i've ever seen in, in some 40-odd years of owning this bike:




way too much emulsion, in general. i've neglected this motor while working on the race bike:

anyway, i pulled the clutch plate. this is a stock clutch with taiwanese plates, running in engine oil from the open main bearing:



i slathered the new plates with white lithium grease when i put it together, and lots is still there.



even the pushrod is still covered in th e grease i used when i installed it:



to lock up the clutch so i can take the nut out, i use a home-made tool i put together some forty years ago, using a couple of old plates:



it works very well and cost me nothing:



popping the clutch center out requires the usual puller. i bought this many years ago as well. it still works well, so long as i screw it all the way in before i try to pop the center loose with the center bolt.



for the gearbox sprocket, i have an old 3/4-drive socket and a reducer that lets me twist it off with a half-inch breaker bar:



i use an automotive harmonic balancer puller for the engine sprocket,with a couple of bolts i've sized just for the front sprocket:



and so at the moment, that's where we are.



looking at that tensioner,maybe it's time for a new primary chain too.

it was a mess. hurricane ivan ran 30 inches of water through my shop. flooded everything i had up to the second drawer of the filing cabinet in the office. all the electric motors, all the pumps (i was a commercial beekeeper at the time), 40 feet of irreplaceable antique books . . . i don't do books anymore.

filled the rear axle of my two-ton truck through the top breather even. filled the fuel tank of the forklift, and came within an inch of filling the hydraulic reservoir as well.

i drained the bike and ran two gallons of WD40 through it, then started it on oil and drained the oil twice. thought that was enough, but it looks like the gearbox might have needed a bit more.

...not so bad Kevin. I wondered about not too much rust in the primary stuff even in the gbox.
What fucks all here is the high humidity and cold weather.
You would put one of your kids to wrench there to taste the old Brit wrenching then up to ride the beast.

we'll see what i can do. i've got three of them interested in LSR, but i'll have to do the footwork to get them going.

i resemble that fact. And I would love to see pictures of that driving dog. Blown apart?

Are you going to tap for the plunger while the motor is in the bike? I am very interested in that.

What size bolts did you use? Just saw a tip that said old style head bolts fit them holes. Don't know if it is true or not.

Is this to become your track bike?
If you're using buckshot's kit, it'll be a breeze.

lol, i kept it over 25 years. i guess just for you:



i had a worn-out clutch basket, with worn-out tabs on the plates, and i'd got into the bad habit of starting the bike in neutral and then clicking it into first gear to free the clutch in the morning. one morning, it just went bang at the end of the driveway, and ^^^that was inside.

i've got buckshot's plunger conversion kit, so i'm going to use it to replace the leaf spring.

I used Buckshots jig and was done in minutes... Kevin, what's that lump under the frame? A centerstand? Take it off, lol

gawd yes, i still have the centerstand on it, and it sticks out in a big loop to clear the left-hand pipe that i don't have anymore because it's a 2-into-1 that exits on the right. i don't ever use it, so it will probably go.

this is a 72, so almost all the threads are SAE UNF or UNC, american hardware store stuff will fit. the head bolts are the older british thread patterns, but on this bike the holes in engine and gearbox sprockets are 5/16-24 and 1/4-28, i think, whatever UNF is in those diameters.

nope, this is my old morgo commuter, the one i bought right after my 21st birthday. the track bike is in a pile by the lift. i need to get buckshot's kit back in circulation, so the morgo comes first, then the track machine starts going together.

nothing to do with the LSR except rod bearings and rings, so that machine is on the back burner. although i'm switching out to 17-inch wheels on it, if i can figure out how to make them fit. the front is easy, just spacers, but the back will need a custom-cut narrower sprocket carrier on the left, and then spacer creativity on the right to make the disc brake caliper squeeze into the swingarm.

went to work at 0530 this morning dispatcher looked at me and said:

what are you doing here? the pad's down. they're swapping wellheads. all day.

i said, why nobody call to tell me?

. . . because it wasn't me on duty . . .

so i have the day off, and i'll use it to take the transmission out of the morgo so i can drill it out for a plunger kit. started off by taking off the inner cover. wouldn't come off because i forgot the little bolt down under the right side, but i've long become accustomed to my lousy memory, and when something doesn't move under gentle force, i go looking for things i forgot. took it out and the cover slipped off.

and there was the spring. didn't look as bad as i thought it might, just a bit of wear on the detent part:



i don't know that the spring is as bad as all that. when it works, it works. but it's a bitch to index when you re-assemble the transmission, so i decided to swap it out.

here's the exploding gear dog, too:



it locks the layshaft first gear in place when you select first gear. the one i blew out was stock. i went to raber's to get another and bob said,

why don't you just put a four speed in there? then the used five speed dog you want me to sell you won't destroy your cases when it goes too.

good advice that i didn't take. i think he sold me a used dog for $15:

the five speed i just took out looks to be in very good condition:



no chips on the gear teeth, shafts not galled or burred . . . dogs are sharp and engage fully:



shifter forks all look fine. not overheated, not worn much, not bent . . .



there was some interesting wear on the non-rolling roller part of all three forks, though:



there's no separate rollers on the five speed forks the way there is on the four speed, and the pegs all had these chips or wear spots on the top of the peg. the pegs themselves didn't look like they were worn flat, as the wear was confined to the very top of the peg, the part that doesn't engage with the cam plate. not sure what that's from, but it shouldn't have affected the shifting.

anyway, the gear set i took out looks to be in fine shape, nothing excessively worn, nothing bent, nothing overheated, no galling, chips, all in all a very useable assembly. except for the design weakness in that first-gear dog. but i bought a complete five-speed set up from bikevice on this forum a while back, after he threw a rod in his T140. he sold me all the parts, everything, so this will be a drop-in installation:



and the difference in the first gear locking dog is very clear:

Hey Kevin,

Thanks ever so much for saving that dog for me! Seriously thank for all the wonderful pictures! I hope they last for posterity, as these picture Hosting web sites wink in and out of existence like stars do. Oh how are we ever going to find the intelligent life that must exist like this! With all this vast time and distance. And we pitiful humans live so short a long and brutish life, and must suffer at the hands of warp speed internet changes. But I digress.

Where does this dog live? I have not noticed it in the videos I have watched. It must be tucked in under something, like first gear? Do I have one on my four speed? I guess I must if he were going to sell you one to replace yours. What are the problems to look for with one, that is if it has not exploded.

Sounds like this is what happened to an expert restorer that I know, who was impatient in the spring to ride and started his T140 without clearing the clutch, except that unlike you, he did tear the case apart. Oh the horrible things we do, I do, when impatient to ride! It is practically criminal! And we are summarily punished for it.

OH, I almost forgot. That jig can be used when the bike is in the frame? That info is of practical, and timely use to me.

Oh PS. Some fairly wealthy benefactor should create a trust that manages a web server dedicated to preserving our pictures and advice for future generations. Just think of it, not only do the pictures disappear now, when Morgan goes, and he is probably getting a little long in the tooth now, all these gems of information go. All John Healy's information goes! It all seems so solid now, but it is just vapor! Hermit's most excellent site. Lunad's video. All vapor. poof, gone! Just does not seem right to me. hey maybe jay leno can do something about it. Doesn't sound like Gates or Buffet would be interested, Anyway doesn't take a billionaire. Just a thousandaire. 100K set up right should do it. Maybe 50K.

you know what? i have learned vast amounts of useful information from people posting stuff on this site, so if i have something to contribute, i try to put it up too. but my own Hosting site is imgur, and if it ever goes down this stuff will go too. i could post it directly to the forum, but then i have to edit the pixels down on everything i post.



it's right on the end of the layshaft, outboard of a little circlip:



on a four-speed, you do NOT have one to worry about. only five-speed boxes run this risk. if you do have a five speed, it either works or it's blown up. if you have an early five-speed gearbox like i did, it's really only a matter of time until it goes.mine went at a stop, and just stalled the bike. if it goes at 30 mph, it can crack the crankcases open, apparently.



everybody tells me it can be. i've finished lunch, so it's time to go see.

I just checked an old five speed gear cluster that I have kicking around taken form a 1972 Bonnie. It has the original exploding first gear dog. Is the later dog a straight fit? What else needs to be changed to update the gear set?

Bruce

Kevin, I must have misunderstood. I thought you said, someone suggested you get a used one from a 4 speed. So i assumed the four speeds had one.

Bruce Martin,

Yes! John has posted about this. The early 5 speeds had problems. There are parts in question which should be replaced by the upgrades. If you don't your whole case could be imperil. Although if you don't do wheelies you may be Ok. I am just repeating stuff I read and have no actual knowledge on the subject.

Use the search and type in 5 speed in subject line and John Healy in the poster box, and follow the threads for the real scoop!

i am out of my depth on that. there were several running updates on the five-speed, and i do know that at least one of the gear pairs were made wider, which is why i bought the whole shebang from bikevice, to have a matched assembly. i haven't compared the two sets side by side yet. there's information on this forum about the upgrades, but i don't know whether it's in one place. maybe someone with more knowledge of the upgrades might chime in with a summary?

no, that was the ever-practical bob raber, who had little enthusiasm for the five speed gearbox in the first place. he told me to chuck the whole thing and put in an entire used gearset from a four-speed, which will go right in. going from a four to a five speed takes a bit of grinding, but going the other way is a bolt-in, apparently.

well, i've installed the plunger. start to finish was about an hour, because i go real slow on these things. the kit from buckshot makes it super simple.

first off, i don't like to work upside down, so i flopped the motorcycle on its side, so i can sit like a ordinary human being. i have lots of milk crates for this kind of thing:



next, i covred up the bearings, which i didn't take out. the mainshaft roller and layshaft needles stayed right where they were, but i stuffed them up with a shop rag:

]

had to take off the oil junction box, too,easy to do:



here's buckshot's kit-- everything you need except cutting oil, a drill motor, and some handles:



this is the jig-- bolt this onto the crankcase, and it holds the bushings for everything you need to do:



it fits on with four bolts that screw into the crankcase on the existing inner cover holes:



. . . and that lines up the hole for the tool bushings right over the boss for the camplate plunger that was never there:



you first drill a 3/16-inch pilot hole with the first bushing (i use air to blow the cuttings out):



then a 9/16 hole with the second bushing:



i use thread cutting oil to cool the drill bit. used to use crisco, which worked pretty well, but this has lasted a long time:

next is th elast bushing for the reamer. the reamer clears out a shoulder in the very first part of the hole so the stepped plunger housing can fit in without bottoming out:



there's a collar on the reamer to keep it from going in too far. you can eyeball what you need, or measure it like i did:



if it's not the right clearance, you just loosen the allen screws and move the collar:



the reamer has a weird triangular shank that doesn't fit any of my die handles or wrenches, so i carefully gripped it with some min-vise-grips. i use these on my reamer for camshaft bushings, too, for the same reason:



the tap was easier. not enough room for a handle, but a 6-inch crescent worked fine. the threads inside the bushing guided it in straight. i took it out three or four times to slather it in cutting fluid and to blow out the chips.



after the tap went all the way through and i blew out the cuttings, the tapped hole looks like this:



i bought all the plunger parts from british cycle supply already, so i could just screw it in and see how it fit:



and it fits pretty good:



it isn't absolutely perfectly lined-up front to back, but the tip of the plunger is well within any functional range of centering and clicks just like it should. i'd bet that this difference in centering is no more than what the factory thought was good enough:



and the plunger assembly runs up from the bottom just like it should:



so.

now that part is done.

next is the install of the T140 five-speed into the T120 gearbox, which should be a direct bolt-in.

Thanks. I checked it out and there are six gears/dogs that need to be replaced. I've had the gear cluster for years and never done anything with it, waiting until I need to take my Bonnie apart. Fortunately that hasn't happened yet. The cluster appears to be in good condition so I'll leave well enough alone for now. The fifth gear would be nice though.