Triumph Repair: TR-6 transmission serial #s and overdrive, overdrive switch, electrical circuitry

Question
hello howard . i am the owner of 2 TR-6s ..a 76 and most recent purchase a 74 . The 76 i have had since the early 80's and i have fitted an A type overdrive way back and has a trans serial # of CT or is it CF 57280 ...looks like a CT printed and that is what i am wondering about . The 74 i just recieved has transmission problems in the top 2 gears and the previous owner decided to sell at a reduced price ...great for me.  The car was originally an overdrive model from the factory commission # CF 28609UO ...however somewhere in its history it looks like the original trans was swapped out with a standard trans from what i could see on a hoist . the rear mounts for a jtype are there and were previously used but not with this trans.  The transmission # in the car now is CTor CF once again looks like a CT or even GT ..65195 . i am planning  in the spring to pull the trans and rebuild it with a jtype overdrive i picked up ser# 27119037 -01335 ..my main question is what year is the standard tranmission they swapped out into the car ? and is it CT /CF or even GT prefix ....i thought they were either CC or CF on the tr-6 . As well any info on matching the overdrive to this box with an adaptor plate and od mainshaft would be appreciated . the car still has the overdrive switch on the wheel but i am assuming no other electrical circuitry on the top cover as it is a standard unit . ...enlighten me where and however you can ..otherwise  the car is in excellent overall condition


Answer
Hi Don,
Lots of luck unscrambling that monkey puzzle. As far as the prefixes I only show three, CD, CC and CF. However, there were "CD" prefixes on straight four speed boxes and on "A" OD boxes up to the end of 72. "CF" started in 73 with the "J" box. And Triumph said that "CC" started in 74.

Another factor is in place because you can change most of the internal shafts and gears (and the OD along with it's mainshaft) in several of the boxes.

So playing with the prefixes and numbers may get you what ever you are trying to achieve but don't count on it.

You should contact Moss Motors in CA as they have a lot of number data. They have a web site and phone number on the web site.

Howard