Moss Miata
Automatic to 5 speed swap - Easier than you might think

by Scott Chamberlain -

Last year, my wife and I found the car of our dreams- a mint condition yellow. Well, almost the car of our dreams- it was an automatic. With 2 other Miatas, we initially thought we'd just leave it an automatic, but we kept thinking how much fun the car would be with a 5 speed. And the automatic seriously decreased the car's value. Time to do the swap.

First, understand that Mazda changes more than the trans when installing an automatic. The auto has a different wiring harness, computer, power frame, and engine. Engine changes consist of retarded timing, retarded exhaust cam, and a .4 reduction in compression ratio.Mazda claims about 10 less horsepower for the auto engine. Still, the swap is fairly simple, not that much harder than a clutch swap.

The Parts

To do this swap, you'll need a few parts:

  1. Transmission
  2. clutch disk
  3. flywheel
  4. pressure plate
  5. pilot bearing
  6. throwout bearing
  7. shifter
  8. inner/outer boots
  9. clutch cylinder
  10. clutch lines
  11. slave cylinder
  12. power train frame
  13. speedo cable

There are other parts that are different, but that can be re-used. The auto has a heavier radiator and a higher torque starter. The transmissions are different lengths, but close enough to use the same driveshaft. The automatic computer will work fine in the stick.


Removal of the automatic parts is pretty much a matter of following the shop manual. Get the car on STURDY supports. GET SOME HELP! This is NOT a one man job, without mechanical assistance. A lot of driveline parts have really big fasteners, highly torqued. A 1/2 inch socket set is a minimum. Soak exhaust hardware at least 24 hours in advance, every few hours, especially the studs on the cat.


Again, largely a bolt in affair, with a few tips. Install the slave cylinder AFTER the transmission is in the car. Use new bolts on the flywheel. Remember to bleed the hydraulic system. The wiring harness is dedicated: you will have to splice to connect the reverse switch, and the neutral safety switch. Whether it is the late model trans, or the automatic car, the car will now only start in neutral. I am still trying to figure out the speedo, which will have to be recalibrated.Other than the above, a straight bolt in, including the pedal assembly.

That's about it; you do have a choice in parts- early or late. The late (94& up) trans will fit and does have some better features; better 1-2 synchros, late oil seals, bigger clutch. Since the early parts are no cheaper, I chose a "95 box with 20k on it. The differences are small, though, so don't pass up a good deal on early parts. Whichever you use, you must use the clutch and transmission for the respective transmission. I paid 1000$ delivered for everything I needed, including delivery. I used Mazmart in Atlanta.You can save some money by scavenging; I have seen an early trans for as little as 200$.

Having made the I wonder why I didn't do it years ago. The car just feels a lot more fun with the stick. I can't feel the horsepower difference. The car can now be hopped up without fear of the fragile automatic. And since automatics are so undesirable from a resale standpoint, the car is now worth more. From everything I have learned, this is a swap that couldn't be easier!

Automatic to Manual, Manual to Automatic (’90 ­ ’93)

by Jason Soza -
Juneau Chapter Representative, Alaska Miata Club

Have an automatic Miata and want to turn it into a 5-speed?

If so, you have some options. You can either trade in your Miata for a manual Miata, cobble together all the pieces to convert your Miata to a manual transmission, or buy a manual Miata and swap all the pieces between them, then reselling the Miata you bought as an automatic.

The benefits? Well, in the end, if all goes well, you will have a manual Miata, you will have learned a lot, and you will have spent nothing (assuming you sell the automatic Miata for as much as you bought it!). That said, this is not a weekend project. There is a lot of grunt work involved and as long as you know that going in, you’ll be fine.

First off, it’s important to understand there are some fundamental engine and component differences between a manual transmission-equipped Miata and an automatic.

There are some other differences you’ll encounter here and there, little bits under the dash that need to be swapped (A/T Control Unit, Kickdown Switch, PPF, brake pedal, etc) but for the most part, turning an automatic into a manual and manual into an automatic is a fairly straightforward affair, assuming you’re going to leave the engines and internals alone. The most important tools you’ll need? Attention and patience. Oh, and an air compressor and impact wrench would be handy, too.

One other big tip ­ convert the manual to automatic FIRST. Otherwise, you’ll be driving your newly-converted manual Miata all the time and will have no motivation to finish the other car. Believe me, it happens. I converted my automatic to manual in about 4 full weekends, then drove it all summer and could not motivate myself to finish the other car. After an entire year, I finally did. So seriously, convert the car you DON’T want to drive FIRST.


In the best case, you’ll have both an automatic and manual Miata on hand. This is good because then you can see how both are put together and where things should bolt when you are rebuilding. In any case, here is a more detailed list of parts unique to each car that should be swapped during your project. You might get away swapping some parts and not others and there may be other parts that I simply missed:

- Electrical wiring (comes out in two large sections ­ interior and exterior);
- Factory cruise control, if equipped on the A/T car;
- Power Plant Frame (PPF);
- Transmission;
- Flywheel/drive plate;
- Clutch slave cylinder assembly;
- Radiators (OEM A/T radiators are larger and have a built-in ATF cooler);
- Throttle body;
- Ignition coils;

- ECUs;
- Control stalks, if cruise control was equipped;
- Cruise control on/off switch;
- A/T Control Unit;
- Power supply on back of instrument cluster (blue plastic sheet);
- Tachometer gauge face (O/D Off is present only on A/T);
- Gear shifter/selector;
- Kickdown switch (on bracket over accelerator in A/T car);
- Cruise Control Cancel switch (on bracket over brake pedal in cruise control equipped A/T cars);
- Accelerator pedal/cruise control lever (on cruise control equipped A/T cars);
- Brake pedal (A/T pedal is about twice as wide);
- Clutch pedal.

Also, there’s a 3-piece mechanical switch built into the ignition on the A/T car. This switch is activated by a cable that goes behind the dash that extends when the gear selector is shifted into Park. The basic purpose of this mechanism is to keep the key from starting or turning off the car when not in Park. I first thought I was going to need a locksmith to swap lock cylinders between my manual ignition switch and automatic, but it turns out that it’s a pretty easy task to just move over the three pieces that make up the switch. Looking at the ignition switch from the top, there’s a silver panel held in place by one screw. On the automatic ignition, this panel covers a brass slider, a spring, and a silver ‘wedge.’ Once the panel is removed from both ignition switches, these pieces can be transferred in about five minutes.

Don't be tempted to swap the entire instrument cluster, as I was. I kept forgetting that the odometer goes along with the cluster, so I would suspect that swapping would be considered odometer tampering. Not cool!


When you get to starting the project, it’s good to have some resources on hand in case you run into a tricky spot. For my entire project, I relied on the Miata Enthusiast’s Manual ­ the only problem with this book is that the teardown/rebuild only covers a manual transmission Miata. For all automatic transmission concerns, they simply reproduce charts from the ‘official’ service manual and paraphrase the instructions.

Speaking of the service manual, this would also be a good book to have handy. In addition, there are a couple of websites that can aid in the process:

Miata Parts Diagrams

Miata Wiring Diagrams

If you are subscribed to the Miata mailing list, the other list members can prove to be invaluable in times of need. I can’t even count the number of times I was in a bind and thought I was stuck, only to receive encouragement, ideas, and tips from the list members until I finally solved the problem.

However, if you can change a clutch, you can do this swap. Be aware though: an automatic transmission weighs at least 50% more than a manual transmission. I was able to simply lift the manual transmission into place when reinstalling, but I required help when fitting the automatic.


As stated before, this is a pretty straightforward affair. If you have both cars on hand, it’s as simple as removing a piece from one car and installing it in the other.

Besides the transmissions themselves, the most difficult part of this project is swapping the wiring. Depending on what accessories each car has, it may be necessary to add in your own wiring (in my case, one car had power windows, the other didn’t). If you’re a wiring whiz, you might get by without doing this swap, which will save time since it involves removing the entire dash assembly and heater unit and pulling 3” diameter bundles of wire through the firewall.

What’s different between the two wiring systems? Lots. The automatic wiring has unique harnesses for the A/T Control Unit, the Kickdown Switch, the Cruise Control Cancel switch, the throttle position sensor, the gear selector, and six unique harnesses for the automatic transmission alone (kickdown solenoid, lockup solenoid, etc). In addition, there are some unique connections travelling to the ECU.

Other than that, everything else is pretty easy. Here are some things to watch out for:

- As mentioned, the automatic transmission is HEAVY. Be careful when removing/installing it ­ a transmission jack is nice, a friend to help out is even nicer;
- Jackstands are a MUST. You need the car at least high enough to be able to slide the transmission out towards the rear of the car, about 2 feet;
- The four 14mm nuts holding the drive plate to the torque converter in an automatic Miata were extremely difficult for me to remove. Access to these nuts is through a 3” x 4” hole in the bottom of the bellhousing. Since the drive plate sits in the middle of this access, you essentially are down to a 2” x 4” access, meaning a regular socket/ratchet will not fit. I ended up using a box wrench and fitting it over the nut, I got out from under the car and used my feet to break the initial grip. After that, there’s about 15 degrees of rotation before you have to reposition the wrench, so it can take some time to remove all four nuts;
- On automatic Miatas, there is a bracket positioned under the alternator and held on with one bolt ­ this bracket holds the ATF cooler lines and is not present on a manual Miata. It's very easy to forget to remove this bracket when you have the automatic car up on the stands. Access to it is much easier from underneath, so don't forget it;
- With an automatic transmission, the top passenger’s side bolt can be a real pain to torque properly. From under the car, the bolt is blocked by the ATF cooling lines and wiring. From the top, you have very little clearance. I don’t really have a suggestion on what to do here. I worked with the limited clearance from the top, but you may find other options;
- If you are pulling the wiring, working inside the car is much easier with the seats removed. There are only four bolts per seat, so it’s a quick task that pays off greatly in the comfort it affords;
- When you're pulling the transmissions, I know some people like to remove the exhaust at the cat, rather than at the exhaust manifold. In my case, the cat bolts were frozen solid, where the downpipe bolts broke loose relatively easily. Reinstalling the entire exhaust was not so difficult - simply hang the rear first, then you can manipulate the downpipe into position;
- Related to the wiring - the hood release pull does NOT separate from the hood release cable. The hood release cable DOES separate from the hood latch itself. Remove the five bolts holding the hood release/mount to the car and you'll see how the cable is released. The hood release pull and cable will be pulled with the wiring;
- Additionally, when gaining access to the internal wiring be careful when removing the dash. There are three cables related to the HVAC system that control heat and vents. I neglected to separate one of these cables from the heater unit before trying to remove the dash and pulled off the pressed-on loop that held it in place. Woops.

All in all though, it's a very straightforward process. Just pay attention to what you remove and how you reinstall it, that's the best advice I can offer. I went into this with very little mechanical experience - I had changed my soft top, replaced my brake rotors and pads, and changed my oil - that was about all I'd ever done with a car to this point. I now have two Miatas, one starting as a manual, the other as an automatic, now fully swapped and functional. If I can do it, anyone can.

If you're considering a similar project (or are in the middle of one) and have questions, feel free to drop me a line!

Back to the Garage

14 February, 2008

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