BA gearbox not selecting 3rd very well

[Graeme.crawley]

I have assembled my BA box, now converted to Sq4 mounting and new bearings except the sleeve bearings and the timing side ball race as these were ok.
I find that the gear change works perfectly 1st through to 4th but coming back 3rd is not found most of the time, just false neutral or worse, nearly false neutral accompanied by clcking noises presumably as the dogs try to engage. Sometimes I think it skips third and lands directly on second! This is the second BA box that has done this to me. The first one I still have not solved.
If I remove the Positive stop mechanism and turn the selector cog by hand all gears select with a nice click and work just fine so it is something to do with the positive stop. BUT,
Possibly related somehow; how much end play should the selector shaft have? I imagine if this shaft can move the dogs on the gears can come apart under pressure but could it make selection not work properly which is not obvious when selecting the gears by turning the selector gear by hand?
This one has .3mm about 12 thou - maybe a bit excessive? The selector cog looks to be low and indeed the quadrant gear is only 85% engaged. If excessive which end do i need to pack by .3 mm maybe with a hardened washer? Given the selector cog is lowish, presumably the clutch end of the selector shaft needs spacing but that will pull the selector away from the final gear, might allow the gears to jump out? I did replace the iron bush there but it is exactly the same flange thickness as the one removed.
Another possibility is that the change-box springs are decayed maybe? Perhaps the pawl is not flicking down fast enough? That seemed to be the problem with the other box, I mean the Change-box moved before the pawl had engaged just with friction on the gear lever Shaft where it goes through the change box. I re-bushed the change box but it did not help.
I think if the return springs are getting a bit weak this might happen? Seems odd that I have two with this problem but maybe....
I notice there is wear on the alloy cheeks of the change-box - more correctly on one of them. These are what prevent excessive travel of this box allowing for just one gear selection at a time so I figure if worn, the box travels a bit far and allows the selection to pass through third gear but it feels more like we never are getting as far as 3rd rather than going past it as I have yet to have a BA box with a false neutral between 3rd and second. Thanks for any thoughts, Graeme

[murray.mckenzie]

Hi Graeme,

I had a similar problem with my BA box on my 1937 VB. I had it to bits 4 times before I sorted it. During those strip downs I followed all the excellent suggestions on this forum. I replaced top gear, the sleeve gear and third gear, replaced bearings and made new bushes, checked clearances and end float and still it jumped out.
What I ended up doing I made a position indicator out of a bit of sheet metal as per attached photo. I got the exact position of each gear by moving the gear selector lever slowly by hand and carefully rocking the back wheel to make sure it was properly engaged. Once made and assembled I found when doing a test ride sometimes everything would select correctly but more often than not it was over-selecting as you suspect with yours so it had moved out of the detent on the selector shaft in the box to an unstable position. Mine would misbehave going from 4th to 3rd and the indicator showed it up immediately. Occasionally it would also mis-select 3rd to 2nd. You can make it mis-select with the bike on the stand and hand selecting. Try it moving it fast and also slowly. You will probably notice a difference and for sure you will see it fail to select correctly. It is as you suspect the wear on the spring box. It was a bit hard to work out how much it was worn and I had a couple of attempts at building it up before I got it correct. The good thing is you can do it in the bike.
Since my last repair it has been perfect. I left the indicator in place as it's sometimes handy to glance down to see where you are and to just check all is well.

Hope this helps
Murray

[GuyWalton]

Had this problem when I built my square four box up . The neutral used when you install the foot change assembly isnt the neutral between 1st and second its the false neutral between 2nd and third . The dots need to align when the gearbox is in this false neutral . Dont know if thats how you did it but it wont work if you dont .

[simon.holyfield]

I've seen a few issues relating to the spring box:

1. Cracks in the casting - they do not appear to be very strong, and crack around the hole for the operating peg
2. Loose - rotation or rocking operating peg
3. Collapsed springs
4. The little plates the springs bear on - I have seen them stick in their slots due to burrs

I've also seen the three rivets in the quadrant assembly loose:

[MGriffin]

A selection/jump out of 3rd gear i found was largely caused by the quadrant rack being sloppy on the pivot.
M

[Graeme.crawley]

thenks for the feedback everyone, when I get back to the gearbox I will look into these suggestions. Cheers, Graeme

[Graeme.crawley]

BTW Murray, the selector indicator looks great - Worth keeping on the box even. I meant to ask what you built up, I assume the Alloy of the selector box? This looks like what we call Muck-metal, can it be built up? Graeme