Gearbox syncro confusion

[Chris KC]

Did you work out the cause?

Excessive end float basically. In the right combo of circumstances the sleeve can slide far enough to expose the detent balls and springs.

[andrew34ruby]

I've found, over the years that the 4 speed crash box is actually the nicest to use - if you can cope with double de-clutching all the time The 4 speed synchro is very prone to baulking (i.e. the striking dogs meeting head on, preventing engagement) when the synchromesh is working and also prone to the synchromesh wearing out (which cures the baulking problem). The gearchange is also heavy and ponderous in my view. The crash box is a little slow but the change from 1st to 2nd is usually very slick and the whole unit is beautifully (and no doubt, expensively) engineered, with chevron gears, to cancel out the end thrust produced by the helical cut pattern. The crash box is light and easy to use, once you get used to it. 
However, the 2 and 3 synchro boxes were probably cheaper to manufacture, even after paying the royalty to GM for using their patented gear synchronising invention.

Baulking was a feature of all the Austin gearboxes, right through to BMC days, the 803/948cc A30/35, Morris Minor etc. gearboxes all suffered in the same way. Eventually, for the 1098cc and subsequent gearboxes, baulk ring synchromesh was added, which cured the problem by allowing the striking dogs to slip past each other if they met head on. It was possible to replace the baulk rings to restore weak or worn out synchromesh as well - a much improved gearbox.

As Reckless says, 2SYN is Austin shorthand for "synchromesh on second".

Strangely I've enjoyed all the small Austin synchromesh gearboxes over the last sixty years.

First car I drove was an A30 with 803cc and we never found any problem with it's original early 3 synchro 'box.
Next was an early mk 2 A40 with the 948cc and the same type of gearbox. Again the gearbox seemed fine.
Then an A35 with 948 and again that box was fine.
Following on was my brother's  late A35 van with the original 1098cc and presumably the later gearbox. Didn't notice any improvement in the gearbox.
Then I had a later mk 2 A40 with the 1098 engine and gearbox. Again didn't notice any difference in gearbox.
I also borrowed a 1275cc MG Midget quite a lot. The gearbox seemed no better or worse than the others.
Now I've been driving my 1934 A 7 Ruby for nearly 5 years. Gear ratios seem odd but never a problem changing gears. The synchros are worn and it often need double-de-clutching, but that isn't a problem.

I've never been aware of any baulking in any of these gearboxes.

The first car I drove legally on the road was a 747 sidevalve Reliant with a four speed non-synchro gearbox. That was a challenge! Double-de-clutching was soon mastered but it was very difficult to always get it right. It seemed a tough but crude gearbox made by Reliant themselves. I never looked inside but I got the impression that each gearwheel was big, heavy, and very strong.

[Dave Mann]

Chris is correct, after removing the gearbox top a big hammer and bar put it back in neutral with the balls and springs flying everywhere, I then drained the gearbox and collected all the balls and springs and returned the oil to the box. The car park was at the bottom of a steep hill, the only way back, getting up which required balancing the amount of power versus my left hand holding it in gear. It was sometime before I had the box out and fixed it. That was in 1971, Peter Fearn suffered a similar failure going to Woolaton in 1991, and C Kingsford-Curram on the Alpine adventure in 1997.

[Chris KC]

You did well to get it going Dave. In my case the sleeve had effectively "tipped" off the end of the shaft and no amount of levering and bashing would slide it back again. It finally came off when the gearbox end cover was removed.

I don't think this is a reason to spurn 4-speed synchro boxes, but owners would do well to have a look inside now and then & check for excessive play.

[Colin Morgan]

Thanks - useful to know that end float was the problem - since this can be checked.

[Dave Mann]

I have nothing against 2 synchro boxes Chris.

[Terrytuned]

The gearchange can over throw if the 1st gear slot in the swing plate is too long  not stopping the selector fork, and exposing the balls. Once the selector fork has engaged the gear there should be no space behind it. Photo of stop s/soldered to take up space.     Terry.

[Parazine]

andrew34ruby wrote:

I've never been aware of any baulking in any of these gearboxes.
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It's more of a problem if the synchromesh is actually working well. Once it's a bit worn, the cones can slip a bit and let the dogs engage.

My Big 7 has a genuine 23,000 miles on the clock and baulks persistently; the synchromesh is hardly worn. Lots of grip on the cones - teeth meet head on - baulked.  I've had the same problems with lots of low mileage BMC cars since the 1970's. 
The ones with a few miles on the clock are usually better - if you change down slowly or double declutch!

[andrew34ruby]

andrew34ruby wrote:

I've never been aware of any baulking in any of these gearboxes.
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It's more of a problem if the synchromesh is actually working well. Once it's a bit worn, the cones can slip a bit and let the dogs engage.

My Big 7 has a genuine 23,000 miles on the clock and baulks persistently; the synchromesh is hardly worn. Lots of grip on the cones - teeth meet head on - baulked.  I've had the same problems with lots of low mileage BMC cars since the 1970's. 
The ones with a few miles on the clock are usually better - if you change down slowly or double declutch!

That explains it, thanks. I was not driving low mileage cars!  And I do change down slowly, often double de-clutching.

[Chris KC]

The gearchange can over throw if the 1st gear slot in the swing plate is too long  not stopping the selector fork, and exposing the balls. Once the selector fork has engaged the gear there should be no space behind it. Photo of stop s/soldered to take up space. Terry.

I concur Terry. When this happened to me I was way too far from home to do a proper rebuild, the box was simply stripped, cleaned and re-assembled. But I did have Hescho (Bosnian mechanic who was helping) put a blob of weld on the gate to limit how far the selector could travel. In this condition we made it home from Switzerland, albeit with our fingers crossed.