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From what I can see that doesn't look a bad box; also shows signs of having been worked on relatively recently.
The fundamental issue is that the sleeve has been able to travel far enough along the shaft to uncover the detent balls; if we assume it wasn't designed this way (big leap I know!) you have then to consider what has worn enough to permit this amount of travel - sloppy bearings, worn synchro cones? - not sure without it all on the bench in front of me. It may be a combo of several small things added up. I recall thinking when this happened to me - or at least a day or so later while stuck up an Alp trying to fix it - it had been a bit of a 'perfect storm' of circumstances, a bit of wear, an abrupt gearchange from reverse to first, etc.
For what it's worth - since you obviously have to strip and rebuild:
1. The whole operation is a lot easier if you warm up the case a little before trying to drift anything out of it. Just play a blow torch over it gently for a minute or two. Really makes a difference.
2. Clear some space and lay everything out in order as it comes from the box. Take photos and label things if you need to. Being orderly about it may save a lot of puzzlement later.
Plenty of people here will walk you through it if you get stuck anywhere.
Joined: Jun 2018 Posts: 10 Threads: 2
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Thanks for the thoughts and tips - duly noted and absorbed.
Looking at it in more detail last night, it seems that what happened is that the 2nd gear synchroniser effectively 'hung up' on the 2nd gear syncro cone so that when 1st gear was selected, instead of the 2nd synchroniser moving away from the syncro cone and sliding along the third motion shaft with the first gear wheel, it stayed where it was and the first gear wheel slid along the 2nd synchroniser instead... exposing the balls and springs....
I can't really see any reason why it might have done that and there is no obvious wear, lash or play that I can detect in the box - so the reason for the failure is still a mystery. Nothing else in the oil to suggest any other components are broken etc. The only thing I can think is that the internal ball detent grooves in the first gear wheel (into which the 2nd gear synchroniser balls engage) have worn sufficiently or the balls/springs have worn enough that the gear wheel didn't grip the synchroniser hard enough to pull it along the 3rd motion shaft when I selected first..... but I'm really not sure...
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Larry,
I had the same problem with my Big Seven, and I too striped the box only to find that without the specialist tools
It was ny on impossible to reassemble without seeing little steel balls and springs disappearing all over the place.
So what to do. I put the gear cluster inside a polythene bag, and used a baked bean tin to hold the balls and springs in place whilst
sliding the cluster together, a lot easier said then done! Reassembled and reset the gearbox, and all seemed well, no sign of the balls and springs trying to escape, and all the gears engaged. Refitted gearbox, started engine, selected first gear; BANG!
back to square one! It seems that a gearbox under load behaves differently to one on the bench.
Plan "B" sent the whole lot to Andy Bird, result a perfect trouble free gearbox!
Some times I think its best left to "Those what know"
Just a thought.
J
Joined: Aug 2017 Posts: 2,748 Threads: 31
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If lock up occurred as 1st engaged then the cone may have wedged. But there should not be sufficent travel for the balls to emerge. The hub is not constrained and is free to work its way toward 2nd, so may occur afer a time in 1st. Normally the travel is limited by the cones rubbing but if these are very worn, or the 2nd gear assembly can move away more chance of the balls emerging. Similarly if 1st gear is engaging excessively deep because of selector adj, selector wear, stops filed etc the tottl travel available is increased.
A myriad cunning devices have been devised for assembling synchro balls, which, like ign switches, best done in the middll of a lrge bare room under a sheet!
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I prefer an empty bath with the plug in.
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Car type: Ruby sports trial special .
Just done mine for same thing just strip and replace
syncro hubs and springs not a hard gearbox to do, check
The bearings when in bits not worth skimping on the job
My problem I ask questions that other people don't like?
Like have you got that for an investment or for fun?
Joined: Aug 2017 Posts: 2,748 Threads: 31
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Hi Spannerman
Could you identify a single cause? Larry's photo suggests the cone not too worn.
Whilst 2nd is transmitting power the slight relative movement would seem likely to free the cone. I suppose if changed from 2nd to 1st when stationary, then started with the clutch disengaged throughout the cone might stick. When all the little sipes have gone do the cones stick together? Should the cone stick in other circumstances, the spell in nuetral should free.
If anyone is caught far from home is it possibe to remove the lid and pin punch the balls into place?
On my car I had crack tested the crank and axle ends and did a lot of exploring of back country from locations very far removed from my parents home and any workshop facilities. As my father before me I had complete faith in the car ..... (and no AA membership). I first heard of the wedging trick from a colleague with an A35 who drove 35 miles in 1st!
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30-07-2020, 07:07 PM
(This post was last modified: 30-07-2020, 07:09 PM by larrylamb11.)
I mused over the failure mode for some time and eventually concluded that the most probable cause was wear in the selector (plus normal wear and tear in the gear cluster). The wear in the selector allowed the 1st gear cog to wander beyond it's normal extreme on the 2nd gear synchroniser - either by being forced beyond it's limit by my action on the gear stick or through the torque of accelerating / decelerating in gear whilst I manoeuvred. At the same time the 2nd gear synchroniser reached the limit of it's travel, butting up against the end of the 'box. At this point the machined groove that retains the synchro balls in the first gear cog over-reached and jumped over the balls, allowing them to emerge 'box-side of the 1st gear cog. That caused the balls and springs to force the 2nd gear synchroniser onto the synchro cone and jam the box..... not completely locked solid, but tight enough that further progress is impossible without severe damage.
For me, the 1st gear cog was then jammed where it was as it hung up on one of the protruding springs.
As to whether a bush-side repair would be feasible, with some ingenuity and a fair amount of swearing I think it could be achieved within the car through the aperture left by whipping off the top cover.... It would be a matter of persuading the 2nd gear synchroniser back into the 1st gear cog or levering the 1st gear cog back over the synchroniser.... you'd have to extract any hung up springs etc. before attempting such a bush-fix, but it looks feasible and indeed Dave Mann reports doing almost exactly this some years ago when this failure beset him in Switzerland. A magnet on a stick would be invaluable in the toolkit to fish out balls and springs previously released into the oil and should prevent having to drain the oil from the 'box. You'd wreck the 'box pretty quickly if you found yourself unable to stop immediately or forced to carry on in 1st....
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Glad you managed to get it sorted Larry.
I think the answer to Bob's question is 'cumulative wear' on all components which results in the theoretical possibility of uncovering the detent balls. I suspect it's then a certain kind of gear change which turns the theory into a reality - perhaps a brisk switch from reverse to first?
'Twas I up the alp in Switzerland Larry; though I read Dave's contribution with admiration. I guess if you can manage to fish out all the balls and springs the selector itself should still prevent two gears engaging at once - if you make it the first hundred yards then no reason not to keep going! I must say in my case though the gear was very firmly jammed. I did try to lever it with such tools as were available but it wouldn't budge even a fraction. No choice then but to strip the box. It held us up by three days but we were able to continue the journey under our own steam. The good news is in no case mentioned so far was much damage done, so once you have the box out you should get away with simply stripping and re-assembling.
