A-series gearbox problem

I'd say it's near certain you have damage to the first gear teeth on the layshaft which the reverse idler engages with. This could have been caused by rough treatment of the 'crash' first gear, or wear on the layshaft bearings causing the gears to drop out of mesh slightly. Either way, you're into a major gearbox overhaul. As a minimum, I'd replace the layshaft and bearings, first gear, and reverse idler. Oh - and the synchro baulk rings while you're at it, and of course check all the other bearings

- especially the first motion shaft one.

Not cheap, I'm afraid, so a secondhand one might be the best option assuming you can strip and check it first. Removing the side cover is enough to *carefully* examine the gears.

Beware of cheap 're-cons' using secondhand parts. These are usually well less than satisfactory.

I used to autotest a tuned-up Sprite many years ago, so I had plenty of=20 experience with over-stressed gearboxes. (With practice, less than two=20 hours from driving into the garage to gearbox free!) I found that they'd=20 run with one or more teeth missing from first or reverse (as long as=20 they weren't adjacent) but I never found that to cause jumping out of=20 gear - just a *very* loud whine. More likely to be something in the=20 selector mechanism at a guess, but I can't help you there. I tried repairing them on several occasions, but the result was always=20 noisy so I gave up. I think once the teeth have settled into a wear=20 pattern, once it's disturbed it's very difficult to get the preloads=20 right. Much easier to get another from a scrappy then; now I don't know=20 . . .

Dave

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I've known selector forks to come loose on the selector rods in these boxes. That could give you the symptons you describe. Whatever it is, I don't think you can do much with the box still in the car. If it's of any interest I have 2 A series g/boxes. Both from Morris Minors. May not be the right type, but they did come out of running cars. I wouldn't like to say how good they are, only that AFAIK they are both working boxes. Mike.

The message from "Mike G" contains these words:

They are different. Back in the 70s I bought a crap D reg Midget and shortly thereafter lost 2 gears. (2nd and 3rd IIRC). On dismantling the box I found the internals didn't correspond exactly to the diagram in the Haynes Manual (so what's new?). Turned out that the Minor 1000 box fitted had a brass or bronze locating washer for the gear cluster while the real thing had a more robust arrangement. I rebuilt that box but replaced it with a proper one from a scrapyard shortly thereafter.

Roger

A D reg Midget should have had the baulk ring box which 1100cc Minor

Yes. Which is why cheap re-cons are always noisy - they only replace the broken parts. IMHO, for a satisfactory job virtually all the internals have to be renewed.

The Midget/Sprite ratios are different from the Minor, otherwise the boxes are similar. I have costed out replacing all the bits that wear and it's about £100 - except the laygear of course which is megabucks if you can get one at all. I agree, there's really no alternative here to a proper rebuild.