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MG MGB Technical - Synchro rings

I am rebuilding my gearbox and have noticed the synchro rings are a bit worn.
The query I have though is that all the books and websites list a single part number for synchro rings 12H1028
The MBG manual says that there are two types for 1/2 and 3/4 and they are no interchangeable
In my gearbox I have the two types mentioned. What is the story, can they be renewed by the one part or are the un shouldered 3/4 gear 1/2 type required to make it work properly, as per the manual?
Neckieman

I realise this may not be as clear as it was meant. The two #'s were 88G397 and 12H1028
All that seems to be available is 12H1028 for all rings and they are listed as interchangeable.
The original manual says they are not interchangeable and the parts look physically different, is this correct?
Neckieman

What gearbox type do you have - 3 syncro or 4 syncro? How did you determine they were a bit worn?
Mike
Mike Ellsmore

Some interesting comments on syncros from the MGAGURU
http://mgaguru.com/mgtech/gearbox/gt110a.htm
Mike
Mike Ellsmore

Compared to pics of new ones they look worn, they still seem to be working but since I have th gearbox apart to replace noisy bearings I thought I may as well do i properly.
It is a 4 synchro box
Neckieman

Any thoughts at all? The manual definitely says 1/2 and 3/4 gear synchro rings are not interchangeable on 4 synchro boxes
Neckieman

While being well aware of the differences between the two types and having conscientiously fitted them in the right place wherever possible, I have never been able to work out the functional difference between the two and why they can't be interchanged. Perhaps a small difference in the cone angle is all I could think of. Or maybe there is something more obvious and I can't see it because I am having a "boy look" as Brownyn calls it!

Where new ones have had to be fitted 22H1028 as noted above is all that's available that's what has been used, with no apparent ill effects. But then the ill effects may not show up for 000s of miles.
Paul Walbran

They do actually look slightly different, the 1/2 ear version has a shoulder not on the 3/4 version.
Neckieman

Yes, that difference is obvious and shown in the manual in the contect of identification, but I can't see that would affect how they work. What I was referring to was the apparent lack of any other differences that would affect how they operate.
I'm very curious to know what it is, presumably the emphasis on this in the manual is for a reason.
Paul Walbran

I ended up replacing all four with the currently available part, as this seems to be normal practcie now.
Time will tell if there is any real difference between the two parts and why the manual says both sets are not interchangeable
Neckieman

This thread was discussed between 28/05/2016 and 14/06/2016

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