False neutral on a Triumph 3HW, the box is stuck twixt 4th & 3rd

[T8Hants]

My 3HW went out for its first test ride since 1947 yesterday and although it performed well in the lower gears going around a field, its brief foray onto the highway to check 3^rd and 4^th resulted in a permanent false neutral between them, when my test pilot attempted to change back down to 3^rd.  I understand false neutrals are not unknown in Triumph gearboxes.  Any suggestions what to look out for when I disembowel the naughty thing?

[Ron]

I've just rebuilt my 5SW box (Same as 3HW) The cam plate and or rollers can wear, also the teeth either or both ends of the quadrant. So to the plungers and springs in the gear change mechanism in the outer cover. Also lining up the teeth in the correct location to obtain all four gears can go wrong.

I also replaced the bearings (sealed bearing at the sprocket end), the bushings in the sleeve gear and the kick start and gear change bushes. A new Clutch basket/plates/rollers/springs. 30 odd test miles and all is lovely so far. Ron

Edited April 10, 2022 by Ron

[T8Hants]

As the bike was only taxed for 9 months in 1947, I am assuming the  5009 miles on the clock is genuine.  All bearings were replaced during the rebuild and I didn't notice any undue wear on the cam plate.  It is possible I did not position the plate correctly when I put the box back together.  It has changed up and down in the lower gears quite happily several times, it was only when it went up to 4th that it hit a false neutral coming down again, which was fortunate as we had to push it home.  No other gear could be selected afterwards.

[T8Hants]

I have now rebuilt the gearbox twice now, since the problem was detected, both times without success, as its either stuck with a false neutral between 3^rd and 4^th and won’t shift.  This was with the cam plate positioned at 4^th as per handbook> rebuilt it again with the cam plate in the neutral position as suggested by a YT video, with the result I can change between neutral and 1^st, but it won’t change up to 2^nd and above.  There was no visible damage to the cam plate or gears.  Are all the cam plates made of Mazak?

[rewdco]

Maybe this article can help you out?

Jan

[welbike]

There are repro cam plates out there, made from bronze, but have no experience with them.

Cheers,

Lex

[T8Hants]

Thank you both for your replies, I have now finally beaten my gearbox into submission aided in my struggle with an article I found online that recomended using the 1st gear position rather than 4th as per handbook. It also explaine the positioning of the cam plate with greater clarity than I had found to date.   I have put the link to the page here as it may help someone else in the future.  It has worked for me.

https://www.hermit.cc/tmc/technote/gearbox/index_cam_quad/index.htm