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Triumph 3HW jumping out of four gear

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Hi Guys,

 

I have finally got the triumph on the road only problem now is it is jumping out of four gear. Just wondering if anyone had any ideas what would cause this before I pull the gear box apart or if it is something I can check with out pulling the gearbox out of the bike. It will still jump out of gear if hold the gear lever up. It stays in gear for a minute then jumps out. I am thinking it is in the shaft itself or the bushings on the shaft.

 

Cheers

Sean

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Hi Sean,

 

I,ve got the same problem!!

 

I removed the plunger from under the bottom of the box and found it has a worn top and the spring is damaged. This plunger goes into the cam plate for the gears, so if the plunger isn't doing its job I'm hoping that's what's causing the gears to jump out. If that ain't it as you say its strip the box!!

 

anyone else had this problem?

 

Andy

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The reason a Triumph gearbox will jump out of gear could be due to one of any number of faults, or more usually to a combination of more than one :(

Fitting a new camplate plunger and spring will certainly help but is rarely the real reason the gear won't stay in. If you eventually strip the box inspect every single item of the selector mechanism becuse it can all wear, and wear means that the movement of the gear lever isn't being translated into a corresponding amout of travel at the selector forks.

The camplate on the 3HW 'box is made out of some sort of monkey metal and the inner tracks can open out quite dramatically, it can also strip away from it's shaft, which is steel, and the mating teeth with the quadrant can wear. If any of these conditions are present replace the camplate. Also check for excessive wear between the camplate shaft and the steel bush in the casing.

The selector rod can wear which in turn makes the selectors twist on operation - the same one was used on all pre unit 'boxes so it's an easy fix.

The selector fork ends can twist (due to wear in the preceeding components) or just plain wear out, as can the pins for the camplate rollers and the rollers themselves. They can be reclaimed, but it's not an easy job. Unfortunately the gearbox was redesigned for 1950 and the selectors are not interchangeable so new ones are a bit thin on the ground.

At this point all you're left with are the gears themselves which are usually indestructable when used on the 350. A quick look will tell you if something is amiss.

As an aside, another weak point on these 'boxes is wear on the floating bushes between the layshaft and the layshaft high gear. This can sorted by hard chroming the layshaft slightly oversize and reaming the bushes to suit - funnily enough, there's rarely any wear between the bushes and the layshaft high gear, which is a plus.

Hope this helps,

Stef

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Hello, as Stefano said I also think that your cam plate is the problem. The original part was made of a very soft material and wears easily out! But the good news is that you can re place it with a steel cam plate from a later Triumph pre-unit gearbox.

 

Will post a picture of a failed cam plate.

 

Guy

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I have seen these cam plates in brass rather than monkey metal. Not sure when/where they derived though.

 

Ron

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Here you have the picture of the cam plate that failed in my triumph 3hw gearbox.

IMG_1357.jpg

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I have seen these cam plates in brass rather than monkey metal. Not sure when/where they derived though.

 

Ron

 

I've got a brand new one of those hanging around somewhere, mine is Italian manufactured, one of the miriad of aftermarket parts that were made out here after the war

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DR boots Ron, size 9. Now Ron the material off these cam plates is really soft and not the right stuff for a cam plate.

 

When the cam plate brooked it stayed in 4th gear, thank god I was not for from home and had to anticipate a little bit if I was coming to traffic lights.

 

Guy

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I was with some of our Dutch friends in Carrantan this year. One was on a B31 that jambed in top gear. We started the bike up on the rear stand with wheel spinning. Then there was a lot of clutch slipping through the traffic in town, but made it easily the 45 miles back to camp. Ron

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I know Ron, I was with your lot on to the American sector.

 

Guy

 

Better not hijack this tread , do you remember last time we were naughty.....

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My memory!!! Yep sorry for high-jacking the thread. I got carried away. Ron

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I have stripped the gearbox. I found that the cam plate rollers have been welded to the shift forks. I also found some wear on second gear on the mainshaft. It looks like second locks four gear to the shaft(?). Can anyone tell me if this gear looks worn on the end. The gears seem to rounded off at the end. Also what is the diameter of a new cam plate roller and how wide are the tracks on the cam plate for the rollers to run.

3hw gear.jpg

tri 2.jpg

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Its fixed, I replaced the cam plate and also the shift forks with new rollers as the rollers had been welded on. Even on the bench it shifted better. Now I have fourth gear awesome! I was able to leave the gearbox in the bike and just remove the clutch and outer gear box covers. Thanks for the help guys hope it might help someone else.

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