RX8Club.com - AT to MT swap

This is not your average conversion thread asking how much it would cost or how to do it, so please keep flames and bullshit out of my thread.

This is the first thread and I am probably the first person (that I am aware of) to post that they have DONE IT.

This is intended for future use of other enthusiasts who may wish to do the swap. I'm not going to give a step by step, but rather a general idea of what is necessary and how to go about it. I will give a few hints and tricks I learned along the way to save money and time for others.

My car was an early build 04 AT with 117,800 on the original engine and a reman trans. I bought it dirt cheap with the intention to convert and mod it at some point. I drove it for over a year as an AT to learn how the car responds and drives, while gathering parts and information for the swap.

I bought almost all the necessary parts for the swap from one single parts car to simplify matters. I had to source a few parts via eBay, other parts sources, and new from Mazda when they were not available used.

Here is the list:

-complete 6 port engine with all external parts, manifolds, injectors, flywheel, and wiring harness (including the wiring that goes from the battery terminal, to fusebox, to starter). Of course I rebuilt the engine before use since I can do so for just a few hundred dollars in parts cost and a few hours of labor.

-6sp trans, I chose to have mine gone through before install to replace the questionable/troublesome 2nd gear synchro

-MT starter (if possible the upgraded/high torque starter is greatly preferred)

-clutch parts (I used stock stuff but you could always buy a new clutch kit instead)

-6sp carbon driveshaft if available, however YOU CAN USE THE AUTO DRIVESHAFT WHICH IS STEEL BUT DIMENSIONALLY IDENTICAL. IT should not have a major impact on driveability or acceleration, if any at all, but it is heavier than the carbon MT shaft.

-clutch slave cylinder, master cylinder, hard line and soft line (I bought a SS braided line for a little over $20 instead of using the stock rubber line)

-shifter assembly, knob, boot, inner trim ring (goes inside the silver trim ring on your console, which will get reused from your automatic)

-clutch and brake pedal assemblies (be sure the clutch pedal comes with the rod that actuates the master cylinder, some people remove them). The pedals I found had the pretty aluminum pads, so I also bought the matching accelerator pedal and dead pedal that also did, but this is completely optional/cosmetic and doesnt have anything to do with the swap itself. From what I could tell the accelerator pedal was identical. Also hope that they leave the switches on the clutch pedal for the starter interlock and cruise switch.

-dual oil cooler assemblies with plumbing. You need both coolers, with mounting brackets, and mounting hardware. Be sure to get the ducts that go between the coolers and bumper. There is a long hard line that goes between the coolers, and the shorter hose between the front of the engine and the passenger cooler is also different and must be obtained. The driver side cooler, and it's plumbing, are technically identical to your stock AT's driver-side-only cooler.

-MT steering wheel (to get rid of the paddles which will be useless)

-MT gauge cluster (for the higher rpm tach, to eliminate the AT warning light, gear indicator, etc.)

-MT PCM. Here is where it gets tricky, read more below about this.

-MT ABS pump from the same car the PCM came from.

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Here are some hints and tricks I learned along the way.

PCM/KEY/CAR COMPATIBILITY:

I got the PCM from the MT car but then it wouldn't work with the keys in my AT car, because of the transponder chip in the key. The PCM is programmed to look for a specific key chip, and so the MT PCM was still looking for the keys from the car it came out of. As a result, I was initially unable to start and run the engine using this PCM.

I was able to plug my AT PCM into the MT engine harness and fire it right up using my stock keys. One plug from the MT harness will not fit into the AT PCM, this plug operates the auxiliary ports etc. and are not necessary to start and drive the car so it can be left unplugged temporarily.

The AT and MT cars use different injectors, and as a result I would not take the MT engine (with MT injectors) above about 4000rpm due to the fuel flow differences, or risk engine damage as a result. I was breaking in a fresh engine so this was fine by me regardless.

I went to one dealer tech and he said he could not make the MT PCM work in my car, and was afraid to touch it. HE recommended that I try to obtain the original key(s) and ignition cylinder that matches the MT PCM I got, from the same car. HE said if I did this, I could install it on my car and the PCM would be happy and start up.

I was able to find a dealer tech "with a brain" as some others told me I would need to find at a different dealership. He was able to set up the MT PCM to work in my car, with my existing keys and such. Everything in the car then worked except for TCS and ABS. Even my cruise works, and in fact I don't have a clutch pedal switch for the cruise control installed.

Apparently the MT PCM would not communicate with my AT's original ABS unit, so I tracked down the ABS unit that came from the same car as the MT PCM, hooked it up and it regained ABS/TCS functionality. There is probably a way around this, perhaps my dealer tech didn't know how to program the original ABS unit in my car to communicate with the new PCM for some reason. For me this was the easiest method, but I am sure there are other ways to resolve this issue.

WIRING/CLUTCH PEDAL SWITCHES:

I am still using the AT dash wiring harness and engine-bay wiring harness. The only differences in the dash wiring SHOULD be related to the clutch pedal switches. I found this easy enough to get around...the cruise already works, so no need for wiring up the cruise clutch switch.

For the starter circuit I ran a wire from the ignition switch, to the clutch interlock switch, to the starter trigger terminal. On the end of the ignition switch, find the white wire with blue stripe (at least it was on my car), in a group of about 6 or 7. Probe this terminal with a DMM (grounded elsewhere) to be sure there is 0vdc+ when the key is off, or in the ON position, and then 12vdc+ when the key is turned to START.

Once you have verified this wire is the start trigger, splice onto it with a T-tap or similar and run your new wire down to the clutch interlock switch on the clutch pedal bracket, it will be the switch closest to the firewall and the pedal pushes the switch finger down when the pedal is pushed. This will be the switch on the back of the pedal near the firewall. Polarity does not matter, just that one wire goes in and one more comes out. I used a spare fuel injector plug/pigtail since my AT dash harness lacked this connector, one from an older nippondenso square style fuel injector, it went right into place like it was made for it. My ignition start wire goes to one wire on this plug, and the other wire on the plug then gets run through the firewall down to the starter. I found that it was really easy to follow the hood release latch to the firewall, cut a slit in it's grommet, slide my starter wire through into the engine bay, and pull it as needed.

Instead of running the new wire down to the starter solenoid small terminal, you can go for a cleaner install and reuse the stock starter wiring. Instead you can run the new starter wire into the engine bay fusebox. Remove the lid on the fusebox and locate the 4 plastic tabs that hold the center section into the outer body of the box, and release them so you can lift up the fuse/relay panel out of the box to get to the wiring underneath. Locate the starter relay "labeled ST" and look underneath it for the light green/red wire. Your new starter wire is going to splice into this wire. Drill a small hole in your fusebox near the bottom and run your starter wire in through it, and splice onto the wire. Reinstall the panel in the box. Now your starter circuit is complete, and requires the clutch pedal to be depressed for the engine to start, just like stock. IF you get a no-crank, use your fingers to fully depress the clutch switch manually, and check using the key turned to start.

IF it operates then, that means your clutch pedal is not fully pushing the switch, and you must either adjust or shim the arm on the switch. I had to do this to mine. I checked the extra distance needed to fully depress the switch, which was about the width of my fingertip. I removed the little green plastic stopper from the clutch pedal that pushes against the switch, and taped on a spare nut (from a bolt) onto it, in order to push the switch further, then it worked perfectly.

OTHER MISC INFORMATION:

The steering wheel is a direct bolt on/plug in, you reuse your original airbag. I didn't even need a puller for my wheel, I just removed the big nut and pushed hard side to side on the wheel and it released from the splineshaft/column. BE sure to have your old wheel centered before removing it, so you can re-center your new wheel and not have it sideways while driving down the highway.

The powerplant frame is identical between auto and manual. No need to change.

The exhaust is identical between auto and manual.

The hole and mounting points for the shifter assemblies are identical.

I did not install the VFAD on my car, I simply capped the vacuum nipple on the intake manifold that operates it.

Again, you could technically use the automatic driveshaft (steel, fat, heavier) with the MT conversion, but I used the manual driveshaft (carbon/plastic, skinny, lighter) since I had it. They are dimensionally identical as far as the mounting points and length, including the front yoke/splines.

The hole is already cut in the firewall for the clutch master cylinder, there is a plastic filler plate there that simply pops out. The master cylinder can then slide into place, and the clutch pedal slides onto the MC studs inside the car, and then you use 2 nuts to bolt it together on the firewall. I did have to unplug and remove the trans control module (TCM) for the AT, which is bolted in place of the clutch pedal.

The clutch master gets it's fluid supply from the brake MC, and there is a hose that goes from the clutch MC to the brake MC reservoir. The res. has a casting for the nipple, but it is not present. I took my res. off of my BMC (it disconnects via a locking pin underneath the res.) and drilled a hole into it, then inserted a brass fitting that I could connect the clutch MC hose to. This needs to be done with care, you do not want to develop a leak here which could cost you your brakes and clutch while driving. Alternately you could probably order the MT version of the brake MC reservoir with the nipple already cast in.

The firewall of my AT already had the clips that hold the clutch hard line so it went into place like factory. The mounting studs for the bracket that holds the hard line and soft line to the firewall, near the oil filter, are also present on my car so it was also a bolt up affair like stock. THen it is simply a matter of bleeding and adjusting the clutch pedal via the rod and locknut inside under the dash.

The rearend gearing and LSD appear to be identical, as are the halfshafts.

GAUGE CLUSTER CONCERNS:

The MT gauge cluster plugs directly into the stock AT dash wiring and everything seems to work normally. IT did take a few minutes for my gas gauge to come up to the proper level, it seems to have a buffer that slows it's movement a lot. I did have the presence of mind not to install this before going into the dealer for the PCM programming...because the mileage information on the odometer is stored IN THE CLUSTER. As a result, the MT cluster shows lower mileage than my AT car has on it. Dealers always document mileage during any service, so if I had plugged in the MT cluster before taking it in for service, CARFAX would have picked up a mileage rollback discrepancy which would follow the car for life. To avoid this, I waited until the dealer was done to install it.

I did inquire about programming the mileage of my car into the MT gauge cluster, and was told it would probably not be possible to do. Apparently when a cluster must be replaced, a new one is ordered, and the cluster manufacturer (apparently subcontracted by mazda) asks the mileage that the dealer wants put into it before shipping it out. They will apparently not service used units due to possible legal issues.

BRAKE PEDAL SWITCH:

The automatic uses a long cable that runs from the ignition switch, to the brake pedal switch, to the shifter. I had to remove this cable so I could swap pedals, and so that the ignition cylinder would be unlocked without the auto shifter going back into park. For the time being, I removed the cable from the brake pedal switch/housing, since I was not sure how the switch came off of the pedal bracket because I couldn't see it very well.

Once I got the pedal out and compared it to the MT brake pedal, I discovered that this switch would not install onto my MT pedal. Then after studying it for a while longer, I learned that the AT switch actually comes apart in 2 halves, and the upper half (the electrical part) WILL install onto the MT pedal. So then it was all good, I installed the switch with a simple twist, and it plugged right back into my dash harness like stock. I imagine that the MT car uses the same switch, just without the lower half/housing that the AT adds on. The purpose of this lower housing is to accomodate the cable that runs from the ignition to the shifter, though I admit to having no clue why it needs to run through the brake switch.

Once the switch was plugged in, I did have to adjust pedal height to get it to work properly. This switch controls when your brake lights come on as you touch the pedal, and my lights were stuck ON all the time.

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That is all I can think of right now. Hopefully this puts to rest some of the bullshit spewed on this forum routinely about AT to MT conversions.