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#864129 11/24/21 9:46 pm
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I know the early 5-speed gearboxess in the '71 and '72 650s were upgraded after suffering failures. A guy whose expertise I respect recently told me that the same thing happened in 1973 with the first-year T140s and that my bike (BH258xx, built in February 1973) has the early, wimpy gearbox. I have not been able to corroborate this through an online search. Is it true that the T140 5-speeds were upgraded after the first year?

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Why is it still working?


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How long have you had this bike? Maybe someone upgraded it before you got it. They do fail without warning. I did mine so long ago {30+} years, I'm afraid I don't remember all the parts that are needed.


1968 T120R
1972 T120RV
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All ‘73 TR7RV & T140 get the improved 5 speed. However later in ‘73 the layshaft 5th gear was widened & secured on right side of 5th with snap ring to prevent it migrating towards 4th gear. Snap ring is not visible. Hidden under gear. The early 73 layshaft 5th gear has straight sides. The improved wider 5th gear has wide taper towards 4th.
Only a few of these early gears failed. My bike built April 73. Had straight side 5th gear. Did not fail. I got new version layshaft as replacement. The teeth on gear were just worn out. The teeth on 5th gear itself had pitting. From wear or rust?? 36k miles. I bought bike new.
The very earliest ’73 may have had wider Hoffman 5th gear bearing. Mine had later bearing. Later year got groove in high gear spline for sprocket oring. Sprocket splines chamfered to accept oring. New lock tab washer must be used with grooved high gear splines.
According to info no ‘73 was sold with the flimsy earlier 5 speed. Maybe a few 650 slipped by, but no 750s. They all got the big fist gear dog & related parts.
Don


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You should be OK with a BH build, as stated above it will not have those weaker early parts.


1968 T150/TR6R
1970 TR6
1970 TR6C
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If yours had the early five speed components it probably would've already broken. My May of '72 T120V broke the lay shaft between third and fourth gears. When I opened it I saw that the weak first-gear dog had already been replaced, scars in the bottom of the case indicated that the original had broken. I ended up replacing the lay shaft with the latest parts, as well as the later main shaft high gear and bearing.
I'm still wondering what I'll find when I get into the gearbox on my September '72 T150V. It still works, but neutral must be selected while the bike is still rolling.


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Hi David, The 5 speed dogs are steeply back cut which makes them hold into gear tightly.

However any clutch drag at all wants to keep gears locked as well. So you have to move pedal hard to get out of gear. It either won’t go, or let’s loose suddenly & goes into next gear.


Next ride try this. Down shift & stop in 1st. At a standstill blip throttle lightly. Just as the rpm rise peaks & begins to drop the dogs unlock for an instant.

At that moment snick into neutral. Takes a little practice. Once you get the hang of it, super easy. I do this 100% of the time. Give a little gas & let cutch out easy just to be sure it’s actually in neutral.

Try it & let us know if it helps.
Don


1973 Tiger 750
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You maybe ought not to respect your guy

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Hi Charles -

You've probably seen this already, however:


https://vintagebikemagazine.com/tec...-of-a-4-speed-to-a-5-speed-transmission/

Cheers,

Steve


'77 T140J Silver Jubilee
'82 T140ES TMA Royal
‘69 BSA Rocket 3 (patiently awaiting it's turn)
"Vintage Bike". What's in your garage?

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Thank you all for your help on this. TT and Desco: The trans is not working. I bought this bike as a basket case 33 years ago (or so) and I am just now getting the engine together! I wouldn't have thought the transmission had been updated, but thanks to TR7RVMan's description and JubeePrince's link to Vintage Bike, I think it may have the later (1976?) gearset. It has the narrower bearing race on 5th gear mainshaft and the RHP RJ009 roller bearing, but not the O-ring groove as pictured on "the last iteration of the gear" photo in Vintage Bike. See photo below. I began to question all this because I will be buying all of the bearings in the lower end. I wanted to replace the two needle bearings inside of 5th gear, too, but my respected adviser (TinkererToo, turns out he was correct on the gearbox updates) said if they look okay and feel okay I should just clean them and use it as-is because replacing the needle bearings is a very difficult job not worth doing if not absolutely necessary.
What do you all think? [Linked Image from i.imgur.com]

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I do remember that I got rid of the leaf spring and went to the plunger. This bike shifts like it's got eyes. VERY short throw. No grinding. Much fun in the twisty canyons. Much, much better than my 4 speed.


1968 T120R
1972 T120RV
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Hi Charles, Excellent!! You have all the good stuff. Looks to be in good condition too!
I recommend Loctite 574 on sprocket splines. 5 speed splines are prone to leaking. More than you would think…. Mine from factory had Loctite. I didn’t re Loctite. Leaked like made. This time used 574. Bone dry after 200 miles so far.
Don.
Don


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Hi TinkererToo, I don’t get it. Who are you talking too?
Don


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The OP, his expert was a little less than.

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Not sure if all the troubles with the early five speed is actually the singer and not the song. I have the five speed out of one of the five A75RV built for the '72 year in the Wenco frame and have not had a problem with it.
Leaks without the O-ring is not a problem if you seal the end of the sprocket against the high gear.

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My 5th gear broke at moderate speed on a city street. Not being abusive to it in any way. Seal the sprocket and spline with pipe thread sealer.


1968 T120R
1972 T120RV
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Originally Posted by TR7RVMan
Hi David, The 5 speed dogs are steeply back cut which makes them hold into gear tightly.

However any clutch drag at all wants to keep gears locked as well. So you have to move pedal hard to get out of gear. It either won’t go, or let’s loose suddenly & goes into next gear.


Next ride try this. Down shift & stop in 1st. At a standstill blip throttle lightly. Just as the rpm rise peaks & begins to drop the dogs unlock for an instant.

At that moment snick into neutral. Takes a little practice. Once you get the hang of it, super easy. I do this 100% of the time. Give a little gas & let cutch out easy just to be sure it’s actually in neutral.

Try it & let us know if it helps.
Don
Thanks Don, I'll try that. All gearboxes have their quirks. I remember all my old Volkswagens needed a blip to the throttle to avoid a crunch when downshifting into second. My mother used to drive us crazy going into first while still rolling. First was not synchronized, and we couldn't teach her to double clutch.
I'll see the condition of the gearbox this winter, probably replace the high gear and bearing regardless. As I recall there is no O-ring on the high gear. My clutch slips, so that is likely to blame.


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72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
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Same post, same gearbox, different question. My factory "Replacement Parts Calalogue" for 1973 Model T140s and TR7s shows a leaf spring for the camplate detent holder. I know that was the case for the '71-'72 650s, but is thsi correct for the first year 750s, too? My made-in-February-1973 engine has a regular coil spring-and-plunger detent as shown in the 1974 "Replacement Parts Catalogue." The cases have the boss for the screw-in plunger holder cast in, so it's not like someone converted it to the later set-up. Was the 1973 catalogue incorrect or is there something amiss with my engine #? (It is a matching numbers bike and the engine serial number boss has the little Triumph stampings under the serial number.)

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Even the leaf spring bikes had the boss for the plunger. It never was deleted, thank God. It made it easy to get rid of the leaf spring.


1968 T120R
1972 T120RV
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Originally Posted by J. Charles Smith
My made-in-February-1973 engine has a regular coil spring-and-plunger detent as shown in the 1974 "Replacement Parts Catalogue."

The plunger, coil spring and housing are in the Jan. 1973 second edition of the '73 (99-0980) parts book.

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Hi, No T140/TR7 had leaf spring.

When Triumph went to leaf spring they did not change casting, meaning the boss for plunger was retained, but not drilled.

I’ve never seen case with leaf spring that was drilled & tapped for plunger.

We rode leaf spring bikes many thousands of miles. Never a problem. Seems most worked fine.

Late ‘72 production Triumph started making changes in frame, motor. What about the ‘73 on 650? As years went by morphed into T140 motor, with 650 top end. Could this be the best bike ever?

The ‘73 on 5 speed is a really nice transmission in my opinion.
Don


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My 74 T120V has a plunger indexer, just the same as a T140, I'm guessing the 650s switched back to the plunger when the T140 appeared.


1971 BSA B25T (built as replica of proposed 1972 B25T)
1971 BSA B50 Project
1972 BSA A65L
1974 Triumph T120V
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My T65 and TR6RV (both built Aug 72 - JH) had the plunger indexing.


1968 T150/TR6R
1970 TR6
1970 TR6C

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