Syncro hub assembly

[wild_willy]

I am in the process of rebuilding a 4 speed 3 syncro gearbox and as a part of that rebuild I will replace the syncro springs and balls. I notice that where the balls sit on the hub splines when engaged in 4th gear there are slight indents worn over time. Is there any reason why the hubs cant be assembled in a different position so that the balls sit on different unworn splines? Can this also be done for 2nd gear syncro hub as well?

Also what are the reasons for loosing balls from the 2nd syncro/first gear hub? I only retrieved 2 of the 6 from mine with 1 other in the bottom of the box. I'm guessing that too much play in the gearset would cause this but what is acceptable and how much is too much?

[Bob Culver]

Hi WW

The second question was addressed at length recently. Seems not uncommon and often the part escaped balls wedge the synchro cone tightly so the car effectively in two gears and unmoveable. Not convenient far from, or close, to home. On Sevens there is nothing to cause the hub to stay on the markings; it is free to drift away until the cones contact. (Some other makes have the bright spots indented so the hub is captured, but very many are as the Seven) Very worn cones contribute and 1st gear selectors and adj of should not allow 1st to proceed too far rearward. It is imperative you ensure will not happen.
A myriad methods have been devised for assembling hubs, but best done in a plastic bag or under the bedsheets!

[Chris KC]

On your first question, I can't profess to have built enough boxes to know all the answers - but I do remember considering precisely this point on a box I re-built some years ago. I elected to assemble it on an unworn section. The result was extremely 'notchy' at first and didn't feel great at all. After a little time it "bedded itself in".

I'm not sure exactly what your situation is - did you strip the box because the balls have popped out? In that case you will want to look very carefully at end play, perhaps synchro cone wear and give it all a good clean up. And hereafter change gear a bit more gingerly... This happened to me after a fairly abrupt shift from reverse to first. Oh yes, and use the correct oil (engine oil).

Finally I'd be deeply worried if I couldn't find all the ball bearings. Are you sure they are not stuck down in their respective holes?

[Bob Culver]

Hi WW

All covered late July with ref to a Big Seven box. There was no single definitive answer; some have noted that a too thin bearing circlip moves the mainshaft forward slightly which would accentuate the problem.
A moderately worn synchro cone retains fine circumferential grooves.

[wild_willy]

Thanks for the replies Chris and Bob. The gearbox in question was last used by me in the late 60's and seemed to work Ok without any memorable nasty issues. I have replaced the layshaft bushes which were badly worn and re-staked the syncro cone on 4th gear which had come loose. I will replace both the mainshaft bearings  as well because they were badly worn.

The 2nd/3rd syncro hub had a full complement of balls and springs but the second gear syncro was missing 4 balls and some springs.
I will replace these and try a new alignment of the balls on unworn splines which should then be as there were when first manufactured. I take note that Chris has issues when he did this with 1st gear being notchy/baulky to engage. Worth a try I think.

I will also take note of the mainshaft position and reduce any free movement between the selector and syncro hub as Bob suggests. I can see that any excessive movement here will allow the syncro hub to move too far and risk the balls being released into the bowels of the box.

Happy to hear of any other recommendations from people with similar experience and fixes.

Many thanks to all
Bruce