Dunno how can tell cones loose from photos. The cluster seems to have 31 teeth cf 32 normally. Would expect less but different pitch can be used for replacements.
(I have encountered loose cones, one with the splines all sheared off! Dunno what the symptoms are in car but could be curious. What mystifies me is that with most cars with similar synchro there is nothing to prevent the hub migrating after engagement so the other cone rubs. Maybe it often does. Maybe why made of bronze. Maybe why RNs often relatively fast. The Austin box is robust, well made and long lasting; the cones and ridging of the input gear bore probably the main weakness to reasonable mileage. No fragile inter gear thrust washers as plagued many other makes.)
Thanks to all for taking the time to share your experience.
Ian - I will remove the misplaced synchro cone and examine the toothed bore. Although not in the right position it is firmly fixed so hopefully another couple of mm of engagement will help. What temperature should I heat it to? The lay shaft looks the most worn component I have examined so it is re-assuring you don't think it is too bad, despite the grooving it turns smoothly in its bearings and has very little slack. If the lay shaft cluster has been modified perhaps what I thought was an original Nippy gearbox has had a close ratio conversion - this would explain why I have the same problem on both gearboxes.
If removing cone note position. Can be difficult to reseat, esp if the leading edge deliberately expanded. If all cleaned up may be scope for Loctite? Have others used?
There was discussion about new cones a year or so ago but I would not trust anyone to acheive the remarkable spline accuracy required.
I have recut the fine grooves using the edge of a fine tap; not ideal but less tedious then many cuts. Does not extend cone life!
For those who have run out of useable cones I wonder how a simple ring tight pressed on then finished would perform.
I would get it up somewhere around 150c at which temperature there its a reasonable expansion of the bronze but not enough to affect the temper of the gears. When re-fitting the gear should be cold and the ring will drop straight on without any real force, it will immediately cool, shrink and be a tight fit so work quickly. They are a very close fit and it is easy to damage the internal spline of the ring.
Terry appears to be respected in some circles with some experience with gearboxes, so if he is able to stake successfully you may be well advised to simply press the ring back home and stake heavily with a blunt centre punch. I am not promising it will work but you could make the situation worse if you remove and replace the same ring than simply attempting to stake it back in place. I have had several gearboxes come to me where the previous builders staking has not worked, but that is not to say it will always fail.
I would suggest that the Lay gear at least is not the original Nippy item, quite why it has been replaced I would not like to say perhaps some damage occurred in the past?
I took a while but I now have a quiet gearbox, I gave up trying to do it myself and took it to Andrew Bird the A7 gearbox specialist to sort out. It seems although it was an original nippy gearbox with the correct first motion shaft gears the layshaft gears had been replaced with an aftermarket one for some reason. The gear meshing pattern was good but it was a bit tight so Andrew fitted the gears in a scrap casing and ran it on a lathe with grinding paste for three hours - problem solved.
I know that the other gearbox I have has aftermarket gears so I suspect it has the same problem. Congratulations and thanks to Ian Williams who in reply 17 thought this was the problem but was confused by the fact that I thought it was a completely original Nippy box.
