Hi there

Gearbox is destroying my brain

I had a problem getting 4th on the gearbox
took it to bits, bushes were badly worn
replaced the layshaft sprocket side bush with new one
shimmed other side
new selector shaft bush sprocket side, shimmed other one.


small amount of end float on shafts not much
all seems to select when i do it with a spanner on the little cam selector thingy (no selector adjuster thing attatched.)
i got the selector thing on, adusted it to what seemed to be working ok off the bike
test ride... exactly the same problem ha ha
i got 1st, 2nd, good
2 things happen
i go 1st 2nd then trapped in a false neutral, then lift up into third. then takes 3 or 4 stamps on lever to get 4th
or i go 1st, 2nd 3rd, then no 4th, only after a few stamps on lever it goes to 4th
sometimes i get trapped in thi false neutral and cant get out
I think it might be a issue with the selector mechanism
occasionally it goes 1 2 3 4 no problems, once in a blue moon tho ha ha ha
what a headache !!!
any ideas?

Hi Maxwell,
In neutral when looking through the inspection hole are the selector dogs sitting centrally between their corresponding gears? Just thinking that you may have shimmed the wrong end of the shafts, selector forks and dogs worn?

email (option): spacemonkeym@gmail.com

yea i replaced the bushes on sprocket side,
and shimmed the other side

TBH i spent all day putting it together taking it apart, checking it, taking it apart, adjusting put back together, check, take apart bla bla bla bla

i thought after my efforts, at least some small sign of improvement would be present, but if anything seems worse than before ha ha ha

the dogs looked central to the eye, it all seemed to select ok when i turned it by hand, and did not have the selector mechanism attatched. just spanner on the cam thing

Is there any checks i can make on the selector thing

Worn or broken teeth on the ratchet and pawls, worn conecting rod pins, worn pawl springs or the adjustment of the connecting rod.

just been out there night working on the box.

just double checked
if i put a spanner on the gear control quadrant i can easily shift all the gears no problemo.
I can even shift through all by twisting that bit by hand. with selector mechanism detatched.


I wonder weather that certifies that the probem lies with the selector mechanism?
looks like the adjuster arm might have been repaired in the past. also the pawls and stuff look quite worn

Definitely change that control rod, you probably aren't getting enough adjustment and who knows what length it is now. The ratchet doesn't look great either, you should be able to pick up good second hand assemblies pretty cheaply but certainly toss that rod.

email (option): spacemonkeym@gmail.com

yea the rods been welded or somehting

i have it so it seems too long, then one turn and it seems too short.

i have a hunch te mechanism's kind of nackered
seems to be quite a lot of twisty movement in it
looks like the upper pawl has gouged on the kickstart ratchet cog
at some stage

Hi Maxwell,

I agree with Matty on the state of the ratchet plate, the teeth looks to have be welded on and reprofiled as there are some grinding and welding marks visible and the angle of the teeth on the lower end does not seem right to me. I would change it for sure.

Good luck, Michiel / Netherlands

Yes, to give yourself some chance of success good used or new parts are required to replace those damaged bits..These boxes are not the best design when in good condition and there are already a few things to potentially stop them working correctly....Ian

email (option): ian@wright52.plus.com

if i eliminate end float from the selector shaft

the actual selector forks still move side to side due to play between the cam and pin channel
is that a big deal?
seems like eliminating end float from the shaft is futile if the selector arms still move

this make much difference? some wear on the seector

The cam tracks can wear as well, along with the selector fork arms and the selector dog grooves...Usually the worst wear in the track is at the point where it changes direction. Incorrect setting of the box in the past is the main cause of this excessive wear at these points, with poor maintenance also a factor.
These things are now a minimum of 50 years old and up to 76years old for WD types and these days you are up against the effects of an accumulated general level of wear and sometimes, the activities of previous owners who haven't taken the time to work out how the boxes go together or how they work...Play between the pin and track shouldn't be that great if they are in good condition...
With these boxes it is all about 'lost movement' and the causes of that. So correct shimming and setting are important and any wear that increases clearances (backlash between parts) is not only undesirable but can affect the operation of the box...Ian

email (option): ian@wright52.plus.com

yea cool im trying to get rid of most movement as best i can

i have 1234 now, but 1st is verry difficult to select when stationary

so yea nearly there hopefully

i have a question
the gear selector forks on b/m box 49-62 has a different part number to the
selector fork for m - 38-48

are they interchangeable?

The whole selector shaft assembly is interchangeable...but not the arms in isolation, unless you change the pins as well...The difference between the two types is the track width and pin diameter..Also you won't get a perfect gearchange with the box stationary...It is designed to work with the inertia of the moving gears etc. If you line up the selector dog teeth and gear dog teeth manually in each gear position, and the box will then move smoothly from one gear to the next without tight spots you are getting somewhere.....Ian

email (option): ian@wright52.plus.com

I had similar trouble with rebuilding my very worn gearbox, years ago.
Turned out that I had my 2 shims/rings on the mainshaft right behing the small bearing wrong...!
Just behind the bearing is a strong smaller ring, then the bigger thin one (if that's right, from my memorie !)
No trouble anymore.

yea hopefully box will be better now
i re did it again, used some green tea tin to make shims, and a
kronenborg can to make thinner shim
managed to eliminate most play

the selecting 1st gear when stationary could be the clutch they have 8 plates in then I and others take a set of plate out 1 steel 1 friction mine now selects 1st gear like a rolls Royce when stationary did have a really heavy crunch with its 8 plate when stationary

email (option): roger.beck@node6.com