TR4/4A Transmission Rebuild

I have a TR4 transmission that I would like to put in my '61 TR3A but it has a broken reverse gear. I received this transmission along with a lot of other parts from a PO. When I removed the top cover noticed the reverse gear was broken. After looking at the Moss catalog for the TR4 transmission I noticed the reverse gear was installed in the opposite direction (shift lever groove facing rearward instead of forward) from what's shown in the catalog. I suspect this is what caused the broken teeth on the reverse gear since it doesn't appear it would be allowed to fully engage reverse as it should. I have the shop manual for the TR3 which fully covers the '3 transmission rebuild. Is there anywhere I can get similar instructions for the '4 transmission. I have checked past threads and did not find anything. Any help would be greatly appreciated. My plan would be to rebuild this transmission over the summer and install it after the good driving weather is over. Also, other than replacing the reverse gear are there any other tips/conditions I should look for?

Shop manual https://drive.google.com/open?id=0B2H2NJt34OffN2FkZjI2NjktNWJiMy00YWExLWIyNjctOTYzNmI3OTg2ODM0
Good articles (the TR4 is basically identical to the TR250 and TR6, tho there are a few minor variations in later ones)
https://www.buckeyetriumphs.org/technical/Gearbox/GearboxDisassembly/gearboxdisassembly.htm
https://vintagetriumphregister.org/maintain/TransRebuild/TRTrans01.pdf

I do suggest being sure to check the forces, both at the shift hubs and the shift rails. Also be sure to check out the countershaft and its bearings, as they are a known weak spot. I found that the new seals being sold for the shift rails did not fit tightly in the cavity (which will cause them to leak), so I found some Teflon "backer rings" to fill up the gap. (Sorry, I don't recall the size offhand, so this is just for illustration https://www.mcmaster.com/?m=true#9560k39/=1250gwc ) You could also make your own if you want; one suggestion I've heard is to start with the brass washer from a toilet tank water feed line and file down the outside to fit in the cavity.

Oh yeah, last time I replaced the bushings on the main shaft (including the troublesome "top hat" bushing), many of the new replacements were not the right size. I bought several extras thinking I could sort through them, but still wound up reusing one of the originals as it was a better fit. One of the new ones had to be opened up to be a good fit on the shaft and not bind.
Also a good idea to pick up several spares for the big circlip on the mainshaft. It really should be replaced every time you remove it (especially if you don't have the recommended Churchill tool) and it's easy to find that the mainshaft has to come back apart. Last time I reused one (because I'd used up my supply with stupid mistakes), it came out of its slot within a year.

Thanks Randall. After reviewing the workshop manual the reverse gear was definitely installed backward. I'm sure that's what caused the failure. Also, after looking at the manual I realize I have at least one other TR4 part that I didn't know I had. Unfortunately the parts are stored about 300 miles away. I was there last weekend picking up the transmission. That's when I noticed I have a '4 exhaust manifold. I looked at it because it was different than the '3 exhaust. I could have a complete engine that could be a '4 engine and didn't realize it. Guess I'll have to look closer the next time I go. With all the parts I received with my purchase years ago there wasn't any mention of a TR4. Oh well, the transmission should work out great once installed. Thanks again.

I'm assuming you mean TR4A exhaust, since AFAIK the TR4 exhaust manifold was identical to the TR3A.

Must be a TR4A exhaust manifold. Shaped like a header with cylinders 1 & 4 exhausting to one position and 2 & 3 to another. I also have the intake manifold depicted by Moss as the later manifold for the 4A. I suspect the engine may be a 4A engine also. Will have to check the next time I'm at the storage location. I'll have to pay closer attention.