Having dismantled the box so as to replace the roller bearing with the bronze bush (thank you David) I notice some serious wear on the teeth of the 3/4 synchroniser sleeve and corresponding wear on the mating 1st motion synchoniser gear. The gears have obviously not been mating correctly probably for a significant time. It explains why, following replacement of the main bearings a couple of years ago, the gear stick tended to jump up following the engagement of top gear as the teeth settled back into the worn part of the gear.
I hope that the photos i am going to post (if I can work out how) will show the wear. It leaves me in somewhat of a quandary as I don't want to delay the reassembly of the gearbox and I do not know yet whether a new gear and sleeve can be purchased. I'll be looking at all A7 suppliers.
It has occurred to me that perhaps I could reverse the synchro cone gearwheel and thus obtain a deeper engagement of the synchro sleeve but I have not yet attempted to disassemble the first motion shaft to this extent.
Suggestions would be appreciated.
Your best bet is to salvage good parts from another box, preferably a scrap one; or simply fit a better box. I'm not aware of anyone making these parts new.
The dog gears pretty much fall off after you tap / prise off the bronze synchro cones, which should be done as carefully as possible and using a little heat. Replace with Loctite.
As Chris says you need S/H parts, locktite the dog ring and syncro ring in place,(your syncro ring looks OK) then peen the syncro ring in place with a blunt punch. Fit new balls/springs to your replacement syncro hub and renew selector springs, to get full dog engagement on both 3rd and top dogs you will probably have to put a shim between the rear bearing and m/shaft (usually 1mm thick) then re-adust selector fork until the hub covers both dogs when selected. Also make sure you eliminate all end float from layshaft gear cluster by shiming behind front bush (see diagram and photos) Terry.
I'd be interested to know what causes this kind of wear, which seems to affect some gearboxes badly and others, hardly at all. There was a discussion about this recently at the Bristol Club Spares Shed, factors included:
Gritty oil due to no oil changes
Resting the hand on the gear lever for long periods
High mileage
Poor adjustment
I'm ready to be corrected here, but theoretically the synchro cones match the shaft speeds before the dogs make contact, so they should simply slip into engagement. Things which could go wrong here are (i) synchro not very effective (perhaps due to wear or maladjustment), dogs thus trying to engage against inertia (ii) driver shoving the box into gear and beating the synchro, ditto (iii) the dogs will rarely be perfectly aligned, so there must be a little wear as they are pushed into engagement. I suggest the secret to a long life is treating it as though it were a crash box & double-declutching - allow the synchro to help rather than expecting it to do all the work. Naturally things like forgetting to fill with oil (or using an unsuitable grade) aren't going to help.
Chris the wear on Peter's was caused by poor adjustment of the selector fork and the dog only half engaged, worn synco rings or beating the syncros causes burring on the dogs and hub. Most of the boxes I have done have poor fork adjustment second gear seems to be the least affected usually 3rd or top dogs showing the wear, jumping out of gear cases the hub dogs taper wear. Terry.
I am able to purchase the gear wheel from the South Australia Club but so far I cannot locate a synchro sleeve. Today I removed the synchro cone and the gear with the aim of reversing the gear so as to utilise the opposite gear faces, however the gear has a 42 thou deep shoulder at the front end (see photo) which, if I reverse the gear would upset the relationship between the synchro cone and the synchro sleeve and require the sleeve to engage further in order to obtain full engagement. So it looks like I'm back to square one and will put it all back together and adjust the fork rod to get the best possible engagement until I can get the new or secondhand synchro sleeve. Sigh!
Incidentally Terrytuned was spot on. I went back to the measurements I made of the distance the end of the fork rods protruded from the gearbox casings and the measurement of the 3rd/4th rod indicated that it was about 0.1" too far out compared to the correct adjustment as per Mr Woodrow.
