3rd gear problems with BA gearbox

[ian.scott]

For the last couple of years I have had problems with my 35 VH dropping out of 3rd gear under light load. I have changed the mainshaft gears once with no improvement ,then decided to rebuild the box with guidance from Geoff Brown the Club gearbox man.
I fitted another sleeve gear and bearing with better engagement teeth, new 3rd /4th sliding gear, fitted a 3rd gear with the best engagement teeth, checked for play in the gearchange forks, fitted new gearchange pins,checked the gearchange pawl and spring and although no wear visible fitted the best ones, fitted new mainshaft bearing. I dimensionally checked all the gears that I had before looking at the tooth wear. After all this the gearbox was still identical when I tried it.
There is nothing to adjust in the gearchange and I am now at a loss to know what to try, does anyone have any ideas ?
I know there are always boxes on Ebay but very expensive and no guarantee that they are as good as what I have.

Ian

[simon.holyfield]

What about the grooves in the camshaft? I know you said you had replaced the pins, but are the grooves they run in worn at all?

I guess you have looked at the forks many times, but are they straight?

[ian.scott]

No signs of wear on any of the 3 camshafts I have , forks are all straight and a good fit in the grooves of the gears.

Ian

[Vincent.vanGinneke]

Did you fit new springs in the gear selector?
My BA used to jump out of 2nd when changing down, new springs cured that.

[ian.scott]

I haven't yet although it always selects the gear correctly and slips out later, but I'll give it a try . I have also now checked that the gearchange camshaft doesn't have excessive play in the box. I have had this box apart so many times that I am thoroughly fed up with it and will try anything.

Ian

[paul.jameson]

I would concentrate on the spring box area. If you have soft springs or flats on the two pivots, you can get exactly the problem you describe.

[nevhunter]

I always carefully check the "DOGS" where the gear engages for tapered wear and how much they engage by. If the gear is sloppy on the bush it doesn't help either. 3rd is the one looking at you when you open the gear section of the box. Some have bushes and others are steel/steel The bushed one may be stopping the (dumbell") double gear engaging far enough. I reckon if the gear is bushed , the sliding one has to be counterbored BOTH ends. Sometimes it's only done on the large gear, end. You should be able to machine it out with a carbide tip or ceramic, if you take it carefully. Only needs 2mm to be removed. Nev

[john.whiting]

Nev s on the right track there,check the marks on the gears for engagement.A lot of these boxes have only marginal engagement which soon wears taper and jumps out.I increase the engagement by reducing the distance between the gear faces,and also face off the slider and gear dogs to partially remove tapered teeth.I read somewhere that these boxes had poor dimension controll of the main bearing bore depth and casing joint facing.Some people dismiss this as a bodge,which it is,but without new parts its the best you can do.I have a NOS BA Burman meant for an AJS V twin,but will use it in my last Panther.Regards John.

[ian.scott]

Hi John,
I have picked all the gears for best tooth shape and the sliding gear is a new one from the Club.
If I have to machine anything,I will cut down one side of the change fork and build up the other side with silver solder to move the gear position more into engagement, although that will inevitably move the 4th gear further out of engagement.
One of the difficulties is that you cant see/measure the gear positions as they are not set until you bolt the intermediate cover on.

Ian

[ian.scott]

I always carefully check the "DOGS" where the gear engages for tapered wear and how much they engage by. If the gear is sloppy on the bush it doesn't help either. 3rd is the one looking at you when you open the gear section of the box. Some have bushes and others are steel/steel The bushed one may be stopping the (dumbell") double gear engaging far enough. I reckon if the gear is bushed , the sliding one has to be counterbored BOTH ends. Sometimes it's only done on the large gear, end. You should be able to machine it out with a carbide tip or ceramic, if you take it carefully. Only needs 2mm to be removed. Nev

On my BA the only gears that are bushed are on the layshaft ( at least on one layshaft) and the sleeve gear.

Ian