mwpayne

My 79 transmission has zero 3rd or 4th gears (bought used a couple of years ago and just installed it).
Will local shops fix these old beasts, are parts available, or should I locate a good replacement?

j_tso

iTrader: (2)

If a shop can do a Miata transmission they should be able to do ours.
There are bearing & synchro kits out there, but for things like shift forks you'd need to look up the part numbers on foxed.ca and check for availability.

PoulsboRX7

Rather than finding a shop to rebuild your 79 trans I'd suggest swapping in a later FB or FC smooth case trans. While most bearings, synchros, and seals are available, shift forks for the 79 are scarce or NLA. Shift forks, synchros and all bearings are available for later RX7s. To do the swap you'll need the tail and three shift rod dogs from a B2200 trans. It's a direct install with shift and rear trans mount in the exact location as the SA. The 79 shift rod dogs won't work because the 79 uses 10mm bolts for the dogs. 80 and later use split roll pins.

Benjamin4456

Didn't know that 79 used bolts instead of pins for the selectors, I'm sure that knowledge will come in handy eventually. If it's easier you can also hunt down a full 1980 transmission and use the selectors and tail housing from it, or I suppose just use the whole transmission. The former would be a good option if you managed to find a bunk 1980 transmission and a good S2+ box.

Frogman

I see shift forks for sale for the 79's ... Plenty of them too

peejay

I have a complete SA trans that can be used for parts. The tail housing is broken and IIRC the bearings are roached.

I'll never do anything with it but I can't bear to scrap it.

PoulsboRX7

The only shift fork listed as available for the 79 is the 5th/R (3648-17-406) and is the least likely to need replacement. The 3rd/4th (1650-17-404) has been NLA for more than a decade. The 1st/2nd (0290-17-402) became NLA several years ago. Recently, the internal main drive gear bearing (0603-17-210, 0249-17-210B) is also now NLA. The 5th gear bearing (8540-17-613) which is not included in any bearing kit has also been NLA for years.
Your easiest, best option for 79-80 is to swap in a 85 or later RX7 transmission. You can also do 81 to 84 but keep in mind that it uses the same internal main drive gear bearing as the SA which is NLA. The good news about the B2200 is that they're still in the junkyards and for a reasonable price. Interestingly, the B2200 has the same exact 1st to 4th gear ratio as the S3 FB. However, it's not a direct drop in swap because the input drive is the same length as the Miata. So, to install in an RX7 the input drive would need to be shorten. You can find input drive modification instructions on the Mazdatrix website. If you decide to use a B2200 gear set you'll also want to swap in an 81 or later RX7 5th gear set. The B2200 has a very short 5th gear.

Frogman

3rd and 4th gear shift fork is available .. They have em at atkins rotary.

PoulsboRX7

Unfortunately, that listing is mislabeled and is only for 1980 Canadian RX7s. You'll notice that the Atkins listing is for Canadian imported RX7s and not US. For US RX7 imports, the 79 and 80 shift forks are NOT interchangeable. 79 and earlier Mazda manual transmissions used 10mm retainer bolts for shift forks, shift rod ends and shift selector. Beginning in 1980, Mazda switched to using split roll pins to retain shift forks and shift rod ends. The 1980 parts catalog lists four different part numbers for the 3rd-4th shift fork. To find the correct shift fork for a 1980 you would most likely need the original VIN.

Frogman

Odd. This is why I'm going to keep my auto trans. It has a stage two kit and shifts great still. The more i read the more i feel It's gonna be a head ache

peejay

FWIW, I had no problem replacing all of the bearings in a pre 85 transmission. I know it's pre 85 because it had a non synchronized Reverse. From the looks of it and the lack of external switches it was an '81-82 trans.

I forget where I bought the bearing set from, but it was from a drivetrain rebuilder supply company. All of the bearings were Japanese and many of them were actually sealed bearings, which is nice because it means that they won't get contaminated with all the flecks of metal that always end up in transmission fluid.

https://grassrootsmotorsports.com/fo...136340/page40/

Benjamin4456

Not to derail the thread, but there is one quick thing I've always wondered about rebuilding these transmissions. So far every single one I've taken apart has had an output shaft bearing with an outer race that spins free of the transmission casing. Is this normal? Certainly seems like it shouldn't be, but I could be completely wrong. Maybe the answer would help mwpayne decide whether his is salvageable or not as well if it's a common issue.

peejay

The bearings are generally a slip fit in the case, and a press fit on the shafts.

Given how much the aluminum case has to be able to expand and contract relative to the steel shafting, only one pair of bearings can be used to locate the shafts in the trans, the other bearings have to be able to float back and forth.

Benjamin4456

Ah of course, that makes sense, thank you. That explains why they never look worn but are exactly like you said, a slip fit. And this was specifically referring to the rear bearings, aka the ones visible with the tail housing removed (since that's all I'm usually swapping around). Given your description I assume that the front bearings are the ones that locate everything axially.

peejay

Click the link above, I disassemble and re-bearing a smoothcase.

The bearings in the center plate are what locate the shafts, they have the retainer plate that loves to back its bolts out and cause all sorts of issues.