Gearbox Problems!!!

The Bantam gearbox seems to give the most trouble and the most non finishes. There are many ways of making a box more reliable and trouble free. I think the most trouble come's from left-foot gear changers but that may just be coincidence! If you have a gearbox problem post the sypmtoms on the site and others and I will tell you whats wrong? Regards Mike

Although mine is a right foot lever. Try as I may, I have still never yet found 4th 5th or 6th gears. What could the problem be?

Steve

Hi Steve,
I have made modifications to the layshaft bearings and run ball races at both ends to make the shafts a bit more rigid, do you think that this is the reason you only have the three gears?
I have a feeling it may be something to do with the lack of sprockets in your spares box?

Mike,
Any advice, silly or otherwise that will preserve what gearboxs we have out there for racing is a good Idea. A conversation at Cadwell with Pete T also brought up an Idea to modify the rules to include any gearbox as long as it only had three working ratios. this could be checked by Tom at scrutineering and any other time a question on how many gears were being used cropped up , but obviously it brings into play the problem of what box/boxs, and how that would be engineered into the cases.. not an easy thing to sort.
Any comment greatfully received!
Alan

Steve - your box is in perfect working order in that case!! 3 is all you need!

Alan - I don't think its come to using other boxes yet - basically there is nothing wrong with the bantam box its simple and if set up correctly gives no trouble. Availibility is still good! Its just people don't want to buy a box for more than £100? and would rather have money in the bank? than having a spare box. Many road gears can be used or modified to suit particularly on a 175..

Anyone with a gearbox problem - still waiting for your message?

Hi Mike, if you can point me in the direction of some good gearboxes near the £100 mark I'll take two!
The last time I saw one on Fleabay it went for well over £200 if memory serves.
....My money is probably safer in gearboes than in the bank if the rules stay the way they are!

good morning Mike,

Might be a bit unfair this as I have yet to strip the box down, however lets see how good you are!

During the second 250 race at Cadwell

Ex Mick Nash,Left foot change, 175, close ratio box, without any real warning or early symptons, bike shifted smoothly into top gear, and now despite all reasonable efforts cannot shift down the box. All the external linkages appear free, return spring feels intact, ie returns to original position after pressure on pedal is released, but refuses to select a new ratio.clutch operates correctly.

On the plus side I had a cracking view of the racing!

Mike Redhead.

I have heard that it is possible (with machining / grinding facilities) to make a close ratio 3 speed box from road bike parts, as long as you have the original close ratio sleeve gear, and mating gear.

In my experience, gearbox maladies are induced by all the other bits, which can be replaced with selected good condition road components.

I'm referring to bent mainshafts, with or without rounded splines, and twisted splines. Mainshaft sliding gears which wobble when spun on the mainshaft. Mainshaft sliding gears that have a baggy fit on the mainshaft are another good one for jumping out of 2nd. Applies to the layshaft and layshaft sliding gears too.

In my opinion we should make a section available on this site which lists gearbox symptoms and possible remedies.

Mike Faults like yours hopefully should be easy to fix when you take it apart and see whats stuck jamped or broken!! My guess the ball bearing/plunger spring has worn to excess and ball is not being compressed by the selector plate(with the 'v's in it) so instead of going down is trying to come out side ways and has locked it in top -but thats only a guess!! Please tell us what it was when you have it apart....

Pete I agree with all your comments - Also I think Robbie52 and Steve37 are both running on nearly all converted road gears..

Hi Mike

You are correct. At one time all the gears in my box were road or convertered road. However I later installed a close ratio output pair.
The road 19 tooth that gets pressed onto the modified main shaft did split on me once. However I think this was due to too great an interference fit. I dressed the main-shaft a little to remove high spots pressed another 19 tooth gear on and no problems now for 3 years.
The lay shaft does have the needle roller bearing rather than the simple bush.

All credit to Brain White for this modifed box. I think he has done great job.

All the selector components springs etc are bog standard and work fine.
I change the spring that pushs the ball in the notches ever year and thats it. Get the frying pan on

Mike,

Thanks for that, I was thinking that the fault lies within the selector mechanism rather than the gear cluster, however, finally got the bike into the workshop, very late last night, and was in the process of removing the shift linkage,and thought ,I will just try the gears one more time, and heyho the gearbox had magically cured itself! so I am not sure if I have a heat related problem. So the plan is to nip round to Steve Fs Saturday to compare gearboxes and frying pans! will keep you posted on both.

Mike R

Hi Mike,
My guess is the pivot pin for the flag has come loose, the flag is flopping around hence you shift the engine about and then it suddenly starts to change gear.. I had same happen some while back when doing a bit of engine testing.
The pivot is likely to be hanging on the last thread if it has the Miller modification, or the pin that holds the pivot spring is dislodged if it has the standard style pivot.
You will soon see!
Cheers,
Alan

Well there's a couple or 3 answers there for you Mike. My guess wasn't you cluster but your changing mechanism - perhaps i didn't explain it well - wear in the hole where the ball bearing and spring sit. When the ball and hole(and the spring weak) get worn the ball doesn't go down but jams in a 'V' normally 2nd. Its a shame you have un-jammed it before you took it apart?
Steve have you the Brian Mk 2 with square dogs(road) on the layshft sliding gear the one that normally has round dogs ?? Brian and Tom are excellent at converting road boxes into race ones...
Mike

Hi Mike Yes that is right the sliding gears are road gears with the square dogs. It does mean the whole gearbox is offset within the casing by 5mm but that created no problem.

Absolutley spot on Mr Powell, stripped the gearbox and found the ball bearing firmly stuck in the hole, I also suspect the spring is weak, the slot is worn(compared with a servicable spare) I shall replace with new and give it a run out to prove. Thanks for your input, also Alan and Steve F. Sadly the frying pans never saw the light of day so am still unable to confirm if mine is better than Steve's!

Mike R