Diagnosing a gearbox

[K70]

Bmc factory exchange goldseal gearbox in classified parts
If not sold ASAP recycling awaits.
Please private message me.

[1000wannabe]

Thanks for your reply, but you obviously didn't read the reason for my thread. Not only is your gearbox not suitable as an 803 smooth case, it's in the UK and I'm not.

[Peted7202]

As you say stripdown will be required. There is a company here in the UK who supply second hand parts www.mirabelleclassiccars.co.uk. They also export them. The guys name is Andrew Bywater. Here's a document he produced some years ago. https://mirabelleclassiccars.co.uk/gearbox.pdf
Here's a parts listing for various boxes.

Hope this is of some use.

Thanks for all the comments.
The shifter I believe to be correct it also came with the box.
If it was incorrect, I would expect it to cause problems in all gears, not just top.

I spoke to someone with 50 years experience in A series engines and all derivatives of the gearboxes today.
I mentioned the usual suspects (detent springs, balls and shift forks) and he dismissed all of them almost immediately.
Apparently the most common cause of this particular problem is wear in the 3/4 synchronizer and it's dog teeth. Specifically where they mate into the input shaft. The more times it is allowed to jump out of gear, the greater taper they wear. It is the fact that it happens on acceleration and not deceleration that the common causes are ruled out.
The necessary parts are painfully expensive here, also made worse if it is in fact, an early or mid Minor specific rib case and not the last box made or a sprite box as the Minor parts aren't available.

I have no option but to remove the box and disassemble, establish what it is, then most likely search for good used parts.

The most annoying part of all of this is when I bought the car it had a 1098 in it with a smooth case box. We discovered fairly soon after that the 1098 needed a rebuild and I had the choice to either do the 1098 or a spare 950 I had. I was persuaded to do the 1098.. If I had gone with my gut, I wouldn't have had the 1098 done and fail, then redone and then have to go down the gearbox upgrade/ change rabbit hole...
At least I've learnt a lot, even if I have one of the most expensive series 2 minors around now...

[1000wannabe]

It is, thanks. I have seen that pdf overview before, but didn't know about the spares.
My only real problem is that I don't know what car the box actually came from so hopefully stripping it down will help ID it.
The input shaft stamp is pretty much worn off so no help.

[Peted7202]

If you can select the gears mark the input and output shafts and rotate by hand and record the ratio in each gear. should be able to identify the box from these ratios.

[1000wannabe]

Yes, that's easy. Apart from jumping out of 4th it was a nice changing/quiet box.
All I need is a list of the ratios to work out what it is, if it's not a Minor box..

[Peted7202]

Does this help?

[1000wannabe]

Yes, thanks

[1000wannabe]

Well thanks to bad weather I stayed in the shed today and pulled the box apart.
And I didn't find anything horrendous..
The lay gear is no worse than any others I've seen and the end play was 2.5 thou. The layshaft was also good.
I feel there is a bit too much play between the input shaft and main shaft where the pilot bearing is but hopefully a new bearing will help.
The main wear I've found is on the selector shaft and associated plunger.
The box has the ratios of a MM not a miget, but I found that the part number for the selector shaft has a B at the end and no searching on the net explains why. (22A472B)
Of course the shaft seems to be the one thing you can't buy..
There is also some wear on the 3/4 synchronizer outer ring.
Somebody has definitely been in here before as the input shaft locking tab is butchered and the bearings seem pretty good/new ish.
So it looks like the selector shaft will be my biggest issue if anyone has any suggestions..?
NB the input shaft was never stamped properly at the factory and is almost illegible I think it says something G4

[Peted7202]

https://www.ebay.co.uk/itm/382893223610 ... Sw241YhQDT

[Peted7202]

The parts list only show 22A472. it's available. See my previous post.

Well thanks to bad weather I stayed in the shed today and pulled the box apart.
And I didn't find anything horrendous..
The lay gear is no worse than any others I've seen and the end play was 2.5 thou. The layshaft was also good.
I feel there is a bit too much play between the input shaft and main shaft where the pilot bearing is but hopefully a new bearing will help.
The main wear I've found is on the selector shaft and associated plunger.
The box has the ratios of a MM not a miget, but I found that the part number for the selector shaft has a B at the end and no searching on the net explains why. (22A472B)
Of course the shaft seems to be the one thing you can't buy..
There is also some wear on the 3/4 synchronizer outer ring.
Somebody has definitely been in here before as the input shaft locking tab is butchered and the bearings seem pretty good/new ish.
So it looks like the selector shaft will be my biggest issue if anyone has any suggestions..?
NB the input shaft was never stamped properly at the factory and is almost illegible I think it says something G4

[1000wannabe]

I'll see what Mirabelle come up with. I can't believe BMC got bored and just added a letter for no reason..

[Peted7202]

See this post. viewtopic.php?t=59754

[geoberni]

I'll see what Mirabelle come up with. I can't believe BMC got bored and just added a letter for no reason..

It depends on how they were made and what part numbering system lies behind it.
The fact that the original number listed in the Parts List is 22A 472, and you have 22A 472B, implies there was most likely a 22A 472A somewhere along the line.
Did Morris/BMC manufacture all their own internal parts for gearboxes, or did they have them from subcontractors?

A suffix letter could simply indicate a change of supplier; I don't believe I've ever seen a suffix letter listed in any BMC Parts list.

I've encountered such coding practices in my past engineering career.

[1000wannabe]

Well that last thread linked above was just a headache. Imagine working in their spares at the time..

Ultimately, all I care is that the right part goes in and works.
I had been told previously that there were three different sets of internals used in the rib case box and they are not all interchangeable or all available.

So far the consensus is that the box is in good condition overall and it's the 3rd/4th synchronizer, shift rod and associated detent that were the problem. The relevant shift fork also needs replacing due to previous user mistreatment and there's typical wear on the lay gear.
The lay gear wasn't causing any noise or issues in the brief drive I got so may be left as is.