Automatic To Manual Conversion

John Seegers


Let us get a few things straight right off:

If you want a manual car, well, buy a manual car and skip this. But, heck maybe you just found a showroom perfect car, which just happens to be an automatic.

Note that the automatic car has a different factory wire harness than the manual car does. This is not just at the transmission but also throughout the car. I have read it also has a different ECU, less horsepower (detuned -10), and it does have a different radiator as well.

You will see a few other posts about this type of conversion, which, in my opinion, makes it sound much easier than it actually is. If you had a professional 4-point auto shop lift that provided a standing work position and a real high-end transmission jack this job would be easier Whether you remove the whole engine / trans as an assembly is up to you. Some find it easier. Some don't. (personally I just pull / swap the trans) your choice.

I was actually looking for a project like this. I had surgery that sidelined me for close to a year and I desperately needed a project like this to keep me busy. I “bit off more than I could chew” because I wanted to challenge myself as a mechanic. This is NOT a project for someone with limited mechanical experience. If you think you can do this with a “daily-driver” you are sadly mistaken. I have a VERY flexible schedule and I often have uninterrupted periods of eight hours or more to dedicate to working on the car. I have some money to spend on tools and parts, a good garage, plenty of space, good lighting, a great tool selection, an understanding wife and two spare daily driver cars.

Timewise think of it as a Clutch replacement.... Plus an extra few hours ! It all depends on your wrenching ability. The thing that is (was) time consuming was doing it with NO advice or prior experience. Now that a guide, and much information is around as to what works and what doesn't, it's MUCH easier and quicker!

Tool List

These are a few items in addition to the obvious or what I would consider the norm for a job of this size. You are not going to accomplish this with a 3/8” drive ratchet set from Wal-Mart.

Jack stands: Possibly two sizes, you will want to gradually get the car as high as you can to do the work underneath. From under the car you will work on the exhaust, driveshaft, power plant frame or PPF and all the auto transmission pipes and wires. I was able to get the car up to about 2.5’ before I felt I was pushing my luck.

Creeper: You will need to move about freely under the car. Buy one with the adjustable headrest.

Workbench: Strong enough to hold an engine AND transmission which my guess is about 500+ pounds.

Torque wrenches: In pounds from the teens to 120. You will need one that can measure in inch-pounds as well if you plan to do the engine work.

Loc-Tite: Color blue and quite a bit of it in fact. I use it on everything.

Quality low lift floor jack: Must be able to swivel and release very slowly with control. Buy one with a large lift pad preferably rubber coated. You cannot have a jack that drops when you twist the handle.

Note: The jack handle will also work as a cheater pipe for the crank bolt if you do the front end.

Impact gun (cordless OK): Could be done without it but you will regret it and will actually increase your chances of stripping a bolt.

Impact 6 points: In 17mm and 14mm in deep and shallow. These will be used over and over. No substitutes since 12 point are guaranteed to strip some of the bell housing bolts.

Engine hoist: Cheap, Northern Tool sort of thing. Include the engine tilt/screw thing. I used a Torin Big Red set at ¾ ton.

Parts (not including engine work, mistakes, lost parts, etc.)

PPF: This is the rail that runs from the differential to the transmission along the driveshaft to keep things in line. It is different for the manual transmission.

Clutch pedal assembly: This goes inside the car under the dash at the firewall to the left of the brake pedal assembly. I cleaned mine up with a wire brush, hit it with some black spray paint and gave it a new pedal pad.

Brake pedal assembly: No need to acquire / replace the whole thing... JUST the pedal will work just fine !

Clutch pressure plate bolts: 6 of them. Pricey but required- Source Rosenthal

Flywheel bolts: Just re-use the Flexplate bolts.

Slave cylinder bolts: 2 of them I used “hardware store” bolts that I had around.

Flywheel: Used and resurfaced (lighten at your discretion)

Transmission: Used and you hope for the best
Transmission bell housing: Probably will come attached to transmission

ECU the auto ECU will *kind of * work, but it will throw codes since it won't see the info from the A/T that is now missing! (ECU's are cheap anyway)

SPECIAL NOTE FOR 01 up.. NB2 cars present some additional challenges due to the fact that if you replace the ECU you must also replace the immobilizer and re-synch the keys..

Gear lever: Used or new. If used it will probably require a rebuild kit available for about $35 bucks. Be sure to read and follow the instructions on how to rebuild a gear selection lever. It has eight parts that must go in very specific order for everything to work smoothly. SEE OTHER WIKI ARTICLE ON REBUILD

Gear lever boots (top and bottom): Pricey but required. These are the rubber boots not the leather trim boot.

Clutch line (pipe): Runs from the clutch master cylinder to the hose at the slave cylinder

Clutch hose: Runs from the end of the clutch line (pipe) to the slave cylinder

Clutch master cylinder: Mates at clutch pedal at the firewall in engine bay.

Clutch slave cylinder: Mounts on transmission at clutch fork

Clutch assembly: Cover, friction plate, pilot bearing, throw-out-bearing and pilot tool I chose an ACT kit or package.

Misc. electrical connectors: To make pop-off connectors for reverse and neutral switching at transmission

Transmission oil: Redline MT90

Turret oil: GL4

The Job In No Particular Order

  • Mark everything you can and take plenty of pictures
  • Have at least 25 quart and gallon Ziplocs and a marker handy
  • Tag every bag in groups specific to parts
  • Pictures, drawings, tracings, and notes will help.
  • I kept a few poster boards on the wall to make reminders
  • I did NOT try to salvage parts to the automatic as I went. Just more trouble than it could ever be worth.
  • You will read and hear plenty of, “Those things sell for ___$ but when you actually go to sell it you get nothing. On top of that these parts are heavy and shipping them would cost a fortune.
  • DRAIN THE automatic transmission!
  • From under the car disconnect all the crap that is attached to the auto transmission. Trust me there is a lot of it.
  • Keep the wire harness safe from harm but all the rest will become garbage. So the carpet popper tool works well for prying most of it off.
  • You will have hard transmission lines running to the radiator from the automatic transmission which can be cut out in sections and then removed. After cutting them back at the radiator you can just unscrew them at the radiator fittings.
  • Pull the exhaust downtube.

  • Watch the O2 sensors! They will be tight, hard to get free but you want to save them since they are over $130 a piece.
  • Pull the PPF which has some odd bolts – to free up the “foot-longs” loosen first then smack them up with a hand sledge to pop the serrated lock nuts above the frame. You cannot just pull the bolts and expect the frame to come free. You will get the idea once you have done one.
  • Pull the driveshaft (you won't re-use the AUTO shaft)
  • Pull driver’s seat out
  • Pull the center console out
  • Unbolt, unplug, undo everything at the auto gear selector then you can pop it free from up top and pull it out linkage and all.
  • When mounting the clutch pedal you will want to cut away some of the firewall insulation and matting.
  • The Miata slave cylinder is known to be a weak link so consider the “racing” upgrade from 5X or 949 Racing. Which includes a braided stainless hose from the pipe to the cylinder. The hose is also supposed to make the bleeding process easier.
  • Pull the front O2 sensor and wire (1 piece) and set it aside. Do not leave it woven through the back of the engine.
  • The clutch pedal you get may or may not have switch on it, if it does simply remove it. You will just override it at the transmission anyway.
  • Pilot bearing is pressed or tapped in to place. You can use the freeze-heat method or just go for it.
  • You can mount the slave cylinder to the transmission before putting the engine back in.
  • You will never have access to the rear heater core hose like you do when the engine is out (if you pulled it ) so at least do that one.
  • The 1.8 does not have a water plug.
  • DO NOT fill the manual transmission with oil unless you have a way of sealing the driveshaft output.
  • Be sure you have enough wire left on the reverse switch and neutral switch to reach your connectors at the harness.
  • Blue Loc-Tite is a sealant recommended for all clutch fittings – use it or be sorry.
  • We hooked up the starter when the engine was about 70% in.
  • I hooked up and bled the clutch line when the engine was about 70% in.
  • The hardest job here may be getting the front O2 sensor back in place. I ended up running it with the wire loose installing it through the wheel well area and then running it up above along the speedometer cable.
  • I believe that pushing the engine hoist to ¼ ton would be a mistake so you will need to find a way to protect your front bumper from getting gouged up.
  • You can pre-install the new PPF mounting it to the differential and letting it hang or supporting it with a long wire tie through the turret opening in the car. I chose to clean and paint my PPF and used wire ties in tandem with the rather worn plastic clips.
  • The PPF mounting is a fussy bit of work so take your time and bring your patience.

Vacuum Hose

You will need to trace the single vacuum hose from the automatic transmission to the rear of the engine just behind the air intake manifold. Snip it and plug it. If you yank it and forget about it your idle will be all over the place.

Here is an image of the vacuum port without the hose on it.



The automatic transmission has an entire wire harness at the transmission that will be unused except for four wires. You can carefully cut the covering back, isolate the four you need, trim the excess wiring back in stages and rewrap in electrical tape.

The four wires you will be looking for will be:
These control the reverse light.
The reverse light switch is the one on the driver’s side of the transmission.
Once found, isolate them, clean them and add the female ends of your butt connectors. These will plug in to the male ends that you run from the reverse switch. Polarity does not matter.
These control the neutral switch
The neutral switch is the one on top.
These are the two thickest wires in the connector
Once found, isolate them, clean them and add the female ends of your butt connectors. These will plug in to the male ends from the neutral switch. Polarity does not matter.
Four wires isolated and wire harness rewrapped
You can make out the end of the PPF in the image

The automatic transmission has an entire wire harness inside the car at the gear selection lever that will be unused except for one wire.
Note: If you plan to keep speakers, console lights etc. then you will need to keep the harness and figure out what does what.
That wire (shown) goes to the E-Brake.

The automatic transmission has an entire wire harness inside the car at the firewall near the pedal assemblies that requires attention. I have some pictures but little else to go on here. The entire assembly will drop off when you pull the clutch master cylinder hole cover plate at the firewall. I chose to trim as much of the bracket away as I could, stuff them up out of the way and silicone the crap out of them so they did not drop or rattle. We could really use some help here on figuring out what all these parts and pieces do.

You need to jump a couple wires here to get Speedo working (later )

To get SPEEDO working make the following connections

AT TRANSMISSION : Connect the Speed sensor to ORANGE and YELLOW wires (small).

UNDER DASH : (at old A/T controller plug:
Disconnect A/T computer (toss)

connect the Black/White to ORANGE

I just Clip, Strip and twist them. you may fashion a jumper to put in the plug, use vampire taps to jump the 2 or whatever makes you feel good. Just connect them together !

and then, Connect the YELLOW wire to GND.

That's it ! your speedo should now work.

CRUISE CONTROL (if you have one )

All you have to do to get the cruise working is to CUT the PURPLE wire at the cruise control computer (on the kick panel / driver's side )

  • If you pull the engine / trans as a unit
Once the engine and transmission are pulled from the car you will need to set the entire package on a bench. Then remove the 11 bolts that hold the engine and transmission together. Free the transmission from the engine and toss it away. You will be left with the torque converter, which is held in place with nuts. You can access them through the starter hole and with the impact gun get them all free. Next with the impact gun break the six bolts at the crank which pass through the starter gear ring. This can all be tossed since none of it is reused.

The metal gasket or spacer that sits between the engine and transmission will be reused.

Mounting the manual transmission and clutch assembly is pretty straightforward. If you have done a clutch before you can figure it all out.

Extra Images


Wire harness under dash at steering column.
It is not quite as bad as it looks!
The harness will want to fall towards its place and from what I could tell there are no connectors that are exactly alike.


As you can see the pedal assemblies are a very tight fit.


The white box is the neutral switch you can toss.


This part was unplugged on my car so I chose to remove it from the bracket. So far - -So good...


Thought I was kidding about a lot of pipes on the automatic transmission?