Has anyone got a clue as to what gearbox casting number 22A1266 is please?

Is it 22A1288 by any chance?

Google says

22A1288 3 Synchro B-type, Magic Wand 22G231 3.76 Rubber Joint Mini 850
22A1288 3 Synchro B-type, Remote 22G232 3.76 Rubber Joint Cooper 998 (Alternative 3.44 final drive ratio)

But I have a photo of one that is stamped with 12FA which is a 1275cc.
I think they used them Between the 22G333 and the 22G1128.
Does it have a serial number or any numbers on the gearset?

The one I have is identical to this, but no stampings on the raised section where your 12FA is, - it also has steel unis, but no idea what the final drive is!

A search on Ausmini has a few hits, Looks like deluxe and 1100S had them as well.

search.php?keywords=22a1288&terms=all&author=&sc=1&sf=all&sk=t&sd=d&sr=posts&st=0&ch=300&t=0&submit=Search

late MK1 S and 1100S - the standardised 1275 3 synchro casing

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For the final drive you can count the teeth on the pinion and crownwheel. The crownwheel also has a part number stamped on it (as well as the teeth count) if you are able to make it out?

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What type of gear change does it have? remote like a mini or sandwich mount remote like a morris 1100?

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The bitterness of poor quality (or Crappy Workmanship) remains LONG AFTER the Sweet Taste of Low Price is forgotten.

OK, I have it, - It's a 22A1288 casting with the 18 tooth 3.444:1 diff running hardy spicer unis', so it's the "commonised" 1275 gearbox casting for the late Mk1S or 1100S engines used at the end of 1968?
It has the Mini remote, not the rubber sandwich.
Thanks everyone, this forum is tops!

Is it possible this is being confused with the 22A1522 case which appeared to fit between the 333 and the 1288 cases and was for 1275 engines, I believe, and was possibly the final box for 3 syncro B series gears with remote change? It could be fitted with Hardy Spicer or rubber cross apparently
Might pay to ensure the 1288 has enough room to swing a 1275 crank if that is what is being fitted
Cheers

since yours doesn't have the stamping on the flat bit at the right hand side, it's likely to be an 1100S casing and someone might have put a mini diff housing on it. 1100S didn't have the 3.44 or hardie spicers - they had a 4.1 (?) and rubber unis

As gto69 said, check the stampings on the laygear and the crownwheel

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did I tell you that I won a trophy?

Yes, I have two "mysteries" on this car, everything else is perfect for a 1966 September build Cooper S, & please don't ask what all the ID numbers are, but the front panel has the narrow style number plate brackets & the gearbox casting is incorrect, as it ought to be 22G333. I'm just wondering if the gearbox casing was changed when I had it rebuilt in 1995, or whether it was done earlier. Unfortunately I can only trace the car back to 1974 & that is to the bloke that I bought it from 28 years back, (& he can't recall), though he did crash it once, so it may have happened during the repair.
No matter, true to my previous form, I will find a 22G333 case & swap the internals over. - I've already got the correct wide number plate bracket & mountings so the panel beater can fit them up...
Once these two jobs are done, the bucket list will be complete.

"I will find a 22G333 case & swap the internals over."

There was one very recently on ebay, I believe that it didn't get a bid.

_________________
The bitterness of poor quality (or Crappy Workmanship) remains LONG AFTER the Sweet Taste of Low Price is forgotten.