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Mazda Transmission Regearing

Regearing Mazda Transmissions

I DO NOT recomment 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 misinstalling 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 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.
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 redisign 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 coversion 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.

83 RX-7 Transmission (9 KB) 1983 RX-7 GSL 5 speed transmission

Mazda didn't start fixing design flaws in their manual transmissions until after 1984, so I had no intentions on using the hole 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

RX-7 5th gear (28 KB)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 inbetween 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 interchangable 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 comming out of the tranmission 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 pretains 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 interchangable, 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 doner 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 dissassemble 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 doner 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 tailshaft or you might have to use the truck tailshaft. 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.

Center Housing Comparison(33 KB)Left:83 RX-7 GSL Center Housing Right:91 B2200

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.

Tranny Guts(48 KB)Transmission bearing housing and gear assembly.

Ok now for tools, I did this modification a year ago so this may be an incomplete list, but should be most of the essesials. You will need a 10, 12 mm wrenchs, and sockets with long extension, a hammer preferably dead blow, 2 prybars, 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 ziplock 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.

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 appart.

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.

Remote Turret (13 KB)Remove the bolt or pin at the red dot.

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 appart 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.

Tail Housing (22 KB)6 inch bolts and alignment pin.

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 doner 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 pliars, spread the ring appart and slide it off. Clean the bolts bolts and put them in a labeled zip lock bag with the C-ring.

Input Bearing Housing(48 KB)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.