I currently have a 4 speed transmission, and would like to install a 5 spd, since my commute is about an hour, and 4k rpm gets old after awhile.

Which 5spds can I install without having to cut up the interior to get the shifter to fit?

I did try several searches, but couldn't find the right incantation.

 

except for the mount under the body, a 5 spd from an 80 should be a direct bolt in. not sure when if at all in 79 went to 5 spd. anything 81 on will need modification due to shifter position, and it's mount under the body.

 

5spd was optional on the 79. I read that the 79 and 80 shared the same transmission. I was hoping that later, and more available, transmissions would work.

 

For "SA" models (79 / 80) the 4 speed was the standard tranny on S models, while the 5 speed was standard for GS models. The automatic was an optional upgrade that Mazda installed in an unknown percentage of vehicles for customers who that might appeal to. Officially, the automatic was an upgrade to the 5 speed in the GS and cost more. All three trannys were mechanically interchangeable btw S and GS models. The starter was different on the automatic as well as the drive shaft and harness and of course the shift level / shift surround in the cockpit.

81 is when the position of the shift lever changed, making that year and later more complicated to install in SA models. There are several threads here, some where members describe that by changing tail cones around, you can install an FB tranny in a SA without altering the interior. But to just bolt up and drop in, you need to look for an "smoothcase" SA 5 speed.

 

Not sure about the whole 4 vs 5 speed thing, but other than that, nearly any first gen transmission can be swapped in if you keep the tail housing from the original (since the shifter moved in the FB's). The swap is pretty simple if that's something your looking into. Here's a short thread on the topic:

https://www.rx7club.com/1st-generation-specific-1979-1985-18/transmissions-like-lego-what-can-i-build-1131900/

I should clarify that the above is true of the manual transmissions. I'm not sure about the auto's.

 

Yes and that smooth case is a late 80s item, not all 80s were smooth cases. Also to use an FB tranny it has to be 81-82 (or 3?) which you can then swap off the tail section and use the tail section from that smooth case 80s tranny to place the shifter in the right area. There is some moderate modifications need to the shift levers in that tail to make this work I think.

 

Your best bet would be to use a 5spd trans from a 79 or 80. The 5pd SA trans will go in with zero modification and you don't have to mess with speedometer gear conversion and tail shaft swapping and shift rod swapping etc. Its a bolt in deal and you're done. The SA trans is durable and smooth.

 

I have a 85 12a trans with a bad 1st gear synchro u can have it for free if u pay shipping