RX7Club.com - Mazda RX7 Forum - Miata gears in 1st gen case

Here is the text from a write up of how to put a Miata tranny gear set into a Mazda truck (or Rx7) tranny. I did not write it. I just put it here to help the conversation. If you want to see the photos, go to the link posted above.

I DO NOT recommend this modification be done by beginners. Unless you are changing the entire transmission by swapping out the bell housing and tail housing this is not your unbolt/bolt in mod. There are many intricate parts and fasteners. Slightly damaging or mis-installing just one of them can grenade your tranny.

It is well known amongst the Miata racing teams that many Mazda 5 speed transmissions can be modified using parts from other Mazda transmissions. This is because all 5 speed transmissions Mazda made before 93 are made the same way, the only differences comes from slight design improvements in the newer model transmissions. Some transmissions after 93 might work as well but I have not examined any to know for sure.
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 tail shaft, 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 interchangeable with Type II trannies. These trannies where used in the turbo RX-7's, 929, B2600, and MPV.

Choosing a Transmission
Mazdatrix Transmission Page
Because of the popularity of the RX-7 in the racing circuits many places make performance transmissions for the RX-7. These differ anywhere from a simple regearing to complete redesign using simpler and much stronger components. One of these transmissions I have found is designated the MK-5. This transmission uses the stock Mazda casings and the internals are all replaced you also have options for gearing each gear. This makes the MK-5 an alternative for any Mazda type II or III transmission. All components to make the conversion cost about $750.

Guru Motorsports
For my first transmission modification I used a salvaged tranny from an 83 RX-7 GSL. Not knowing anything about what I was doing or if it was going to work at the time I picked this tranny because 1st through 4th gears are the same as on the 87-93 B2200 and 5th gear is a lower ratio. Given the only ratio difference was 5th gear I considered this a good starting place for modifying my transmission.
1983 RX-7 GSL 5 speed transmission (there was a photo here)

Mazda didn't start fixing design flaws in their manual transmissions until after 1984, so I had no intentions on using the whole transmission and although most parts are interchangeable, most would be a downgrade for the B2200. All I was interested in though was the 5th gear. The stock 5th gear in the 87-93 B2200 is .858:1 I wanted to lower this ratio to give me more upper end speed in 5th gear and more gas mileage. My research (Gotta love Solomiata) concluded that the 83 RX-7 GSL tranny had a 5th gear ratio of .825:1 and would do the job I wanted, but the exact ratio of the RX-7 5th gear in my B2200 tranny would be unknown until I could count all the teeth on the input and output shafts and recalculate the ratio.

SoloMiata Drivetrain Interchange Guide
Felix's RX-7 Transmission Suitability
83 RX-7 GSL 5th gear
Basic Terms:

•Bell Housing: This is the housing all the way at the front of the tranny as it sits mounted in the truck. It mounts directly to the back of the engine block and encases the flywheel and clutch. It also contains the front input and output bearings for the tranny. The end of the opposite of the side that mounts to the engine mounts to the bearing housing.

•Bearing Housing: Is the small plate in between the bell housing and center housing. This plate is only about an inch (2 cm) thick and holds the input and output bearings for the center of the transmission. The entire gear assembly is mounted to this assembly making it easy to transfer the entire gear assembly into another tranny.

•Center Housing: This housing encases reverse and 5h gears and is cup shaped. Both the Center Housing and the Bearing Housing are interchangeable with almost any tranny.

•Tail housing: This housing contains the shifting rods and feet. It is at the very end of the transmission.

•Turret: The housing the shifter rides in is called the turret. Some of these are directly on the tail housing like on the pickups, on Mazda's sports cars this is what I call remote mount. The shifting rod coming out of the transmission protrudes out of the tail housing and goes to a turret that is mounted above and away from the top of the tail housing. This gets the turret much higher towards the cab and allows a shorter shifter to be used.

Ok regearing your tranny isn't as easy as swapping gears. Here is some general knowledge you will need to know, all information contained here pertains to pre-93 Type II 5 speeds. All 5th gears should interchange by itself (keyword should!!). 4th gear is always a 1:1 ratio. The two center housings are all built generally the same and are interchangeable, there may be minor differences pertaining to strength. 1st through 4th gears and reverse must all be changed as one unit. You must have the bell housing for your truck. In most cases you should have the option of using your truck tail housing or the one from the donor transmission.
So here are the general processes to regearing your tranny. If you want to keep your stock B2200 tranny but change 5th gear, you simply disassemble both transmissions down to 5th gear and swap the gears. If you want a stock Miata, 626, MX6, etc.. tranny you take the bell housing and tail housing off the donor tranny and put the truck housings on, now it should bolt right in. To get 1st through 4th gears from a RWD 626 and 5th from an RX-7 you swap the 626 bell housing for the one on your truck, then you would strip the 626 housing down to 5th gear and put the RX-7 gear set in. After that you might be able to use the 626 tails haft or you might have to use the truck tails haft. Currently I am working on putting a full Series 5 tranny in my truck, the tranny is in great shape so all I have to do is bolt the B2200 bell housing on, adapt the rear tranny mount and move my shifter back 2 inches and its all set. 2nd gen. RX-7 TII trannies have a better synchronizer design and beefier output shaft, it would require your truck bell housing and a custom made driveshaft using the TII yoke. The shifter location would also have to be moved in your truck because the truck tail housing would not fit with the output shaft being larger.

Left:83 RX-7 GSL Center Housing Right:91 B2200 (there was a photo here)

Shown below is the assembly that is required to change 1st through 4th gears and reverse, basically to make any 5 speed transmission bolt into your truck you just put the truck housings on this assembly. The two center housings are universal, the bell housing is required to mate the tranny up to the F2 block and what tail housing you use is somewhat optional. (there was a photo here)

Transmission bearing housing and gear assembly. (there was a photo here)
Ok now for tools, I did this modification a year ago so this may be an incomplete list, but should be most of the essentials. You will need a 10, 12 mm wrenches, and sockets with long extension, a hammer preferably dead blow, 2 pry bars, or really huge flat head screwdrivers, a pair of needle nose plies, a set of small punches, a bearing puller, bolt puller set, 2 3/8" 2ft long threaded rods, c-ring pliers, snap ring pliers (2 types), a small wooden block, a box of zip lock bags, a sharpie or permanent marker and some breath mints. You will also need a dremel tool or some sort of grinding devise with a small tip. I'm sure a picture would help but at the moment I don't have one. (another photo here)

It makes things a lot easier if you degrease both transmissions before working on them, make sure to degrease the inside of the bell housing as well. Also make sure you drain the tranny fluid out of both trannies before taking them apart.
Pop in a breath mint (no really take a breath mint), transmission fluid fumes leave a real bad taste in your mouth. Stand the transmission up so that it is standing on the bell housing. It is best and easiest to disassemble the transmission starting from the tail housing and moving towards the bell housing, standing it up on end allows the remaining transmission fluid to run inside the tranny instead of on the floor. If the transmission has a remote shifting turret you will have to free up the shifting cup inside the turret. Remove the service plate on the side of the turret and then remove the bolt or pin holding it in place.

Remove the bolt or pin at the red dot. (there was a photo here)
At this point the little square piece that the shifter end sits in should be free to slide around.

If the tranny you are taking apart doesn't have a remote shifting turret like on the B2200 you will be picking up here. Next you will remove the 8 bolts that hold ALL of the tranny housings together. These bolts are 12 mm and are about 6 inches long. They start at the tail housing, go through the center and bearing housing and then thread into the bell housing.

6 inch bolts and alignment pin. (there was a photo here)
Above is the 91 B2200 Tail housing, you can see the shifting turret on the top at the very end. In earlier model transmissions I have seen this turret in the middle of the housing. The yoke shown there is a spare one I have. I use it when removing the transmission to keep fluid from leaking out the back. Mazda makes a similar plug to use. The location of the 6 inch long bolts are shown in blue. The short black line is an alignment pin there are 2 of these. Once you remove these 8 bolts the entire casing of the transmission can be taken appart with some persuasion.

The tail housing should slide right off now, if not give it a little tap on the side with the dead blow hammer, if you don't have one of these use a block of wood in between the housing and the hammer to prevent cracking the housing.
If you are only modifying 5th gear then click "Fifth Gear >>" below.
Fifth Gear >>

The last thing you have to remove is the bell housing, once this is done you can put the truck bell housing on the donor tranny. Start by removing the bolts off the input bearing housing and remove the housing. Next you will have to remove the C-ring around the input bearing. Take your C-ring pliers, spread the ring appart and slide it off. Clean the bolts and put them in a labeled zip lock bag with the C-ring. (there was a photo here)

Remove these 6 bolts.
Take the tranny stand it back up on end and place the wooden block under the input shaft. This will rise the bell housing above the working surface and allow it to slide off without having someone hold the tranny in the air. Take the dead blow hammer and gently tap on opposite sides of the bell housing, it may come off easily or it may take some persuasion. If it won't come off easily try tapping it harder, if using a regular hammer always make sure to use a block of wood as a damper. If you still can't get it to come off take the two pry bars and pry down on either side, be careful not to damage the gasket surface.

You should now have the whole gear assembly which is ready to have the truck bell housing bolted on to as well as the truck tail housing if you choose to use it. Make sure to add sealant to all the mating surfaces. The gear assembly must line up perfectly with the bell housing to get it back in, not only do the bearings have to slide in place but the shifter rods as well.

On the B2200 tranny the whole shifting lever mechanism is contained in the tail housing. Here is where things slowly start getting harder. The next housing you have to remove is the center housing to get this off, first you have to remove the shifting feet. These are the 3 nuckled pieces. They are held in place by a clotter pin. To take off the shifting feet you need to take an appropriate size punch and slowly punch the pins out with a hammer. Get a good image of how the feet interlock before removing them. Be careful some of these knuckles have springs and bearing keepers so if you are not careful parts may fly apart or get lost easily. Put the knuckles and the parts that go with in a zip lock bags and label them.

You may want to remove the gland nut at this time too, although you can remove it after taking the center housing off. This will be a pain in the ass. There is a groove in the shaft that it threads into and the flange of the nut is crimped into this groove. You will have to either grind out the crimp with the dremel tool or straighten it out with a punch and hammer or something. It is a 32 mm nut, you can either find a 32 mm socket or you can take a chisel and tap the nut around.

This is where the hammer and pry bars come in handy (percusive maintenance hehe). Take the hammer and gently tap up on either side of the center housing. You must alternate sides otherwise it will not come off, If it doesn't tap off easily you will have to take the pry bars and wedge them in the crack. You have to be careful not to screw up the sealing surface on the housings here, gently pry up on both sides at the same time. The first time doing this is the hardest, just work with it until you come up with a pretty decent method to getting it off, you will use the same procedure to get off the bell housing if you need to.
If you have not already done so, remove the speedometer gear in the middle of the output shaft. It should come off with a series of snap rings and washers. Pay careful attention to how these are arranged and how you take them off. Putting them back on later is a challenge as well as all the other fasteners for the internals.

You should have something like this now.
This is what the B2200 tranny should look like (Big Ass Picture).
Sorry if the large picture is grainy, I had to compress the hell out of it to make it 56k compatible. In the B2200 tranny you may notice a few things that you do not see in other transmissions and some of them to the untrained eye may like wear on the gears or other internals. Mazda made all kinds of little modifications to these trannies. One of the big ones is the upside down U shaped bracket going over the reverse pin gear which is shown in the picture above. Another is the grooves in the teeth of the gears, these where added to help with lubrication. The edges of the teeth where also chamfered. Mazda also started using sealed bearings in their transmissions. The most puzzling thing is that Mazda removed every 11 tooth on the synchronizers; I have not found this in any other Mazda tranny. Some think this is to make shifting easier but looking at the clutch hubs and the synchronizers the only way to get them to shift better would be to completely redesign them. All the other teeth interlock the same, there for 3 missing ones will make no difference. If anyone knows why Mazda did this email me at Kyrasis6@hotmail.com

Here is where the neat stuff begins, being since fasteners are different from tranny to tranny use the appropriate snap ring pliers and C-ring pliers to remove the rings holding both the bearings on. There are usually washers underneath the rings and sometimes there might be keepers holding some stuff in. I've only seen the keepers on the Dynamic Dampener of the series 5 trannies though. This is where the experience comes in handy, you must be prepared for whatever surprises you may run into.

Once you get all the fasteners off you are ready for the bearing and bolt puller. Purely for the sake of clarity I will start with the counter bearing on the shorter of the two shafts. Loosen the side nuts on the bearing puller until you can get the cup to fit around the bearing, then hand tight the nuts so the bearing puller fits around the bearing. Now take the bolt puller (the bracket with the large pointed bolt in the center) and hold it on top of the counter shaft. Then take the right length bolts out of the set to thread down into the bearing puller. Make sure the bolts are tightened so that the bolt puller sits evenly, or perpendicular to the shaft. If it is crooked the bearing won't come off or may damage the parts. Take a wrench, ratchet and socket, or impact driver to tighten the center nut, this will pull the bearing right off. You basically do the same thing for the bearing on the output shaft except you use the long 3/8" threaded rods to go down the length of the output shaft and into the bearing puller, use two nuts on the threaded rods to level out the bolt puller tighten the center bolt and your done with the bearings. You will have to crank quite a bit to get them off so I recommend an impact gun if you have one. (there was a photo here)

This is the bearing puller.
Bolt & Bearing puller with 3/8" threaded rods.
Now the input and counter gears that make up 5th gear should slide right off, if you already have both transmission torn down to this point you just slide the gears on the transmission you are going to use. It may take a couple of tries to get them to line up just right.

5th Gear before and after (there was a photo here)
This may be a good time to count the teeth on the new 5th gears, you will need to know this as well as the number of teeth on 4th gear (main) to calculate the new 5th ratio. You can also get the gear counts Here. (there was a photo here)

Now press fit the bearings back on, make sure the bearings are sitting perfectly straight. Put something over each bearing to protect it from scouring like a piece of cardboard with a hole cut in the center then take the pipe and gently tap the bearings back in place. Put all the retainers, c-clips, snap rings, etc... back on. This will be the hardest part of the modification. You may get half the transmission back together in a couple minutes and then suddenly spend an hour putting one ring back on, it is a pain in the ass. Now that you got all the gear internals back together put some gasket sealant on the mating surface of the center housing slide it on and tap it in place. Take the shifter feet parts out of the bag and assemble them back on the shifter rods, screw the gland nut back on and tighten it. Don’t forget to crimp the lip back into the recess on the shaft with a punch. Install the retainers that go beneath the speedometer gear, put the speedometer gear on, don't forget the ball and then put the retainers on top.

All you have to do now is put sealant on the sealing surface of the tail housing and get it and the shifting rod back on. I don't remember exactly how I did this but you MUST make sure the end of the shifting rod is in the shifting feet. You can probably let the rod slide out a little bit as your putting on the tail housing to position it and once it is in place slide the tail housing the rest of the way down. Put the long 12mm bolts back through the tranmission housings and lightly tighten them for now. Place your shifter in the turret and run it through the gears to make sure everything is ok. If not take the tail housing back off and inspect the shifter feet and shifting rod. Once your sure you have everything back together right tighten down the 8 bolts and your all set to go. Email questions, details, or suggestions to Kyrasis6@hotmail.com.