gearbox stuck in 4th gear

maylar · Jun 8, 2009

A lovely day here in the North East US yesterday. I attended the annual Brit Iron meet in Auburn Mass with my Commando and came home with the Best Norton trophy... on a flat bed trailer

I had a bit of trouble getting the gearbox to down shift riding to the event, sometimes having to tap the shifter twice. Then on the way home it got stuck in 4th gear and would not come out. The shifter is still centered and moving against the spring but the gears ain't clickin'.

I did have the outer cover off this year to renew o-rings. Could I have assembled it wrong? I'm praying that the trouble is restricted to the outer cover mechanism.

drc

Keith1069 · Jun 8, 2009

Broken pawl spring is my guess, or if it was just about working it needs adjustment, bent so it just clears the pawl when centred.

L.A.B. · Jun 8, 2009

Keith1069 said:
Broken pawl spring is my guess,

And that would be mine too.

I'd never go on a long trip without a spare.

It can be changed easily enough at the roadside with the bike leant over to the left to stop the gearbox oil spilling out!

If a gearbox is being overhauled for any reason, then it's always a good idea to fit a new set of springs,-especially the pawl spring.

79x100 · Jun 8, 2009

Pawl spring failure is a classic. It can undergo a 'greenstick' type fracture on the curve and still function erratically.

As LAB says, a straightforward roadside repair. I always carry a spare in the little Mk111 underseat tool tray .

The selector pawl doesn't look very important but if it's not properly positioned, the gear pedal has no connection to the box.

maylar · Jun 8, 2009

79x100 said:
Pawl spring failure is a classic. It can undergo a 'greenstick' type fracture on the curve and still function erratically.

Right on the money dude. Spring broke in the bend, "greenstick" style - broken at one side, bent on the other.

This is the factory installed spring (I'm original owner so I know). Does it matter which way the dog-leg bend goes? Could I have stressed it by putting it in upside down?

Ron L · Jun 9, 2009

Yes, there is a correct way to install the spring. The "double cranked" leg of the spring is on the bottom. If you fit it each way you will see that there is only one way where the spring fits with the legs straight on the pawl bracket.
Fitting it upside down will not cause the spring to break, but will give erratic or no engagement. These springs wear, rust and generally weaken from time to time, so keeping a spare in the shop (or on the bike) is an excellent idea.

Cookie · Jun 9, 2009

I've found this thread to be a good learning experience. I've never had any problem in this area but those springs are a lot older now.

seaguy · Jun 9, 2009

Same here. Thanks for the pearl. Long way from riding yet but I always listen to experience and take notes as well. Need a Sticky Post here for threads dealing with ideosyncracies of the Commandos.
Rich

seaguy · Jun 17, 2009

Hey Maylar, I just noticed a tiny hole in the round gearbox cover on my 71. It looks like it was drilled as a vent . Have you read anything about this? Don't see the point with the clutch cable hole would accomplish the same thing.

Cookie · Jun 17, 2009

I can't speak for yours, but years ago we used to run a vent out of the gearox to prevent pressure build up putting oil on the clutch. I think in some cases it may need a little more venting, certainly some kind of seal on the clutch rod is good.

swooshdave · Jun 17, 2009

seaguy said:
Hey Maylar, I just noticed a tiny hole in the round gearbox cover on my 71. It looks like it was drilled as a vent . Have you read anything about this? Don't see the point with the clutch cable hole would accomplish the same thing.

That is a vent. Probably a more reliable vent orifice than the clutch cable.

L.A.B. · Jun 17, 2009

Old Britts article: http://www.oldbritts.com/12_065199.html

Cookie · Jun 17, 2009

That's interesting. I used to drill out a grease fitting and run it from the cover so I did not have to drill the box casing.

gearbox stuck in 4th gear

maylar

Keith1069

L.A.B.

Moderator

79x100

maylar

Ron L

Cookie

seaguy

seaguy

Cookie

swooshdave

L.A.B.

Moderator

Cookie

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