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MG MGB Technical - Gearbox (again) weird one!

So I am rebuilding the 4 sync box, with overdrive, and have a spurious part extra!!

There is a 5/16in ball bearing which I cannot figure out where it came from.

I have been through the parts lists and cannot see any 5/16 ball anywhere!

Help!

Colin
Colin Parkinson

Colin
Where the rear mainshaft bearing carrier fits into the housing, some boxes have a ball in a cutout to stop the carrier spinning in the housing
It's not on some parts diaghrams
William Revit

The rear carrier "lock" is a cylindrical bar.

It sounds like one of the synchro hub balls - there should be three in each hub.

Ball bearings are also sometimes used in the selector rod detent assemblies at the front of the box.
Chris at Octarine Services

5/16" ball bearing translates to BLS110, and although that's only listed for the 3-synch gearbox in my parts catalogue it's also shown as the detent on the reverse gear switch plunger on 4-synch - item 31 on page C44.
paulh4

Chris, synchro balls are smaller, and the selector detents are cylindical.

Paul I think you have got it. It is not showing in any of my parts catalogues, but it makes sense.

Colin
Colin Parkinson

Paul, I have found it on an old parts microfiche.

Thanks for your help. (Again!)

Colin
Colin Parkinson

My pleasure.
paulh4

Now then guys, on assembling said gearbox, I have found out where the 5/16 balls came from!! Thanks Chris!

They are under the plungers on the selector rail detents.
The rubber bumper box uses a plunger and a 5/16 ball, the earlier ones use a solid plunger.

So, any thoughts on why the change and which might be better?

And now I need to find the other balls that went missing!

Picture below

Colin
Colin Parkinson

Lol - I have found both, I suspect that it was cheaper to produce a silver steel rod and use a standard ball than to make a pin with a domed end and harden it.

I doubt there is much to choose between them - I have never seen the domed pin wear but the ball usually makes a small dent in the end of the pin - not enough to radically alter its performance though.

The balls usually drop into the case when the rods are pulled out but they can get stuck in their tubes.
Chris at Octarine Services

A picture!



Colin Parkinson

Do you think it might be that the ball type might let the selector move more freely by spinning as the shaft moves past where the solid type might balk up sometimes --maybe
William Revit

Quite possibly Willy, but it took Leyland how long to make the change??

I am going with the balls.
Colin Parkinson

You could always rely on BL for a load of balls!
Nigel Atkins

This thread was discussed between 13/01/2020 and 22/01/2020

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