Originally Posted by MaxDuo

He was wondering if it was some.... Ford tranny.

Originally Posted by MazdaTruckin website transmission modification article

Solomiata references 3 types of Mazda 5 speeds.

* Type I is the really early style transmission used in the RX-2, RX- 3, and RX-4. These where known to be pretty stout transmissions that the later Type IIIs where modeled after.
* The Type II also known as the Model M trannies is what is used in the B2200/B2000. The model tranny in my 91 B2200 is a M519. These trannies where only used in naturally aspired (non-supercharged) cars. These cars include RWD 626, 79-85 RX-7, 86-91 NA RX-7, B2000/2200 truck, and Miata. The main difference in these transmissions are the gearing, bell housing and tailshaft, making these the key interchange parts. The bell housing is basically an adapter to whatever block you are using. It is stated that input and output shaft lengths may very .5" between some model trannies so be cautious which tranny you select.
* Type III or Model R trannies are used in the turbo vehicles. These transmissions are based off the Type I transmissions and have a better synchronizer design and beefier output shafts. Output shaft diameter was increased from 15/16" up to 1" I have not seen parts from these to know if the synchronizers are interchangable with Type II trannies. These trannies where used in the turbo RX-7's, 929, B2600, and MPV.

Originally Posted by SoloMiata Drivetrain Interchange Guide

Mazda has two 5 speed transmissions. One is used in NA applications (AKA 'type 2' or Model M) and came on such cars as the RWD 626, 79-85 RX-7, 86-91 NA RX-7, B2000/2200 truck, and Miata. The other is a stronger unit that came on all turbo RX-7's, 929, B2600, and MPV.

Within the type2 versions only the bellhousing & tailshaft cases and gear ratio's are really different between models. All the guts of the Type 2's are nearly the same and mostly interchangeable. The major differences came in '81 when the shifter was made remote, in '83 where some bearings and shafts were made larger and in '94 with improved seals and a double cone 2nd gear synchro. Between models the input/output shaft lengths may differ slightly (~ 1/2") so always measure. The 79 through mid-83 tranny guts should be avoided if reliability and torque rating is important.

Everyone asks me about changing the Miata 5th gear with that of the 2nd gen RX-7 so that their highway cruising rpms can be lower. The whole guts can be fairly easily transferred but individual gears, unless you are an experienced transmission repair technician and have all the proper micrometers and pullers (and have an idea what you are doing), is not a job for the average shade tree mechanic. The Miata trans also uses a different number of teeth on the input and counter shafts than the corresponding RX-7 transmissions so swapping to the RX-7 5th gears creates a different ratio than the advertised ones. See 5th Gear Interchange Chart.

The turbo trans (AKA 'type3' or model 'R' ) was derived from the original, and more robust, RX-2 through RX-4 5 speed type1 trans. It also has many internal design similarities to the Type 2. It mainly differs from the Type 2 in the input and output shafts grew from 15/16" to 1", a removable bellhousing and the case having strengthening ribs instead of being smooth. For more turbo trans info go to the links page and click on Mazdatrix and Felix's. A variant of the turbo trans has been used in Ford light duty '88-91 F-150, Bronco and Ranger trucks. It is model M50D-R2 and also known as the "Kogyo"

The 99+ Miata 6-speed is made by Aisin and is not related to the Type II 5-speed (it is listed below for reference ony). Will the 6-speed bolt in a 5-speed Miata? Yes, make sure to get the trans plate and shifter from the 6-speed donor since they are unique to it. You will have to use only two of the three 5-speed starter bolts but that shouldn't be an issue, otherwise it bolts in (same PPF mount, etc). Keep in mind the 6-speed is combined with a 3.909:1 rear in the USA (3.636:1 other markets) since the tranny gearing is much steeper so your '90-93 or 99+ 4.30:1 5-speed rear should also be changed to the 3.909 or at least the more common 4.10:1 otherwise you'll have a nice tree stump puller