ZXTuner Transmission Review

I purchased a ZXTuner transmission in June of 2005. After a long wait and many delays, it was delivered in October of 2005. It arrived in a box, well packaged, but with no instructions. Since Iíve done many transmission swaps on my ZX2 and others before, I figured it wasnít a problem.

For the most part, the install went well, however when it came time to bolt the ZX2 front transmission mount bracket to the transmission, I ran into a problem. Since the transmission is made using an Escape transmission case, one of the bolt holes donít line up. Luckily, I had a die grinder and some bits that took care of that problem. When bolting the engine to the transmission, I noticed the transmission had one less place for a bolt than the ZX2 engine does. So, I left that one out. It isnít a problem when driving, but my car failed state inspection because of it. Going by the letter of the state inspection laws, the car technically isnít safe. I ended up find another shop to get it inspected at that overlooked that minor issue of one missing bolt. If it is good enough for an Escape, it is good enough for a ZX2. If that missing bolt really is a problem, you probably can take all the internals of the ZXTuner transmission and swap them over to a ZX2 transmission case and reshim everything.

Here is a picture of the front transmission mount bracket with the hole on the ZXTuner transmission that doesn't line up correctly.

After the transmission was installed, I installed the axles. They took a lot of force to install compared to the stock ZX2 axles. The rings that help keep the axle in the transmission are thicker and stronger than what is on the regular ZX2 axles.

After getting the rest of the car put pack together, I filled the transmission with 75w90 gear oil. Since I planned to change the transmission fluid after the first 500 miles, I didnít use expensive gear oil. It was API GL-4/GL-5 75w90 made by Exxon. After a couple days of driving, I noticed my car was leaving a little puddle of gear oil under the car whenever I parked it somewhere. There was a leak where the passenger side axle goes into the transmission. Iíd check the transmission fluid weekly, but it was a slow leak, basically it would leave a 3" spot on the pavement if I left the car parked somewhere for 8 hours.

After the first 500 miles of taking it easy, not using full throttle and not using high RPM, and trying to vary my driving so that everything that may be new inside the transmission would be properly broken in, I drained the 75w90 and filled the transmission with Redline D4 ATF. From the first time I shifted above 3500 RPM from 1st to 2nd gear, the transmission would grind. It would grind almost every time I shifted from 1st to 2nd above 3500 RPM. So, I tried draining the Redline D4 ATF and refilling it with fresh Redline D4 ATF. That didnít fix the problem. Also, I still had the transmission leak.

I went to the ZX2 message boards for help and was contacted by several other ZXTuner transmission owners that had problems with their transmission. However no one had a solution for either problem. A call to Rob at ZXTuner helped. He said he would send me a new passenger side axle seal and also that I canít use ATF in the ZXTuner transmission even though I can use ATF in the stock ZX2 Transmission. The ZXTuner transmission is built to Ford Escape specs and the tolerances are different. He said he mentioned it on the message boards once before and assumed I knew all about it. I went back and searched, but couldnít find any post by Rob at ZXTuner mentioning that the ZXTuner transmission needed 75w90 gear oil instead of ATF. If there were instructions included with the transmission, I would have never had that problem and I would have saved me the $70 that it costs for the two transmission full ups of Redline D4 ATF.

After draining the Redline D4 ATF out and replacing it with Exxon 75w90 gear oil, the 1st to 2nd gear shift grind went away. After 500 miles of driving with the cheaper 75w90 in the transmission, I drained it and replaced it with Mobil1 synthetic 75w90. Immediately the 1st to 2nd gear shift grind returned at every shift above 3500 RPM. I also replaced the passenger side axle seal at this time. However the leak continued. Around this time, I decided not to return my stock ZX2 axles for the core charge refund because I didnít have any confidence in how long this transmission would last. In the following months, I tried several synthetic and semi synthetic 75w90 GL-4/GL-5 gear oils and every single one of them would cause the transmission to grind if it was shifted from 1st to 2nd gear above 3500 RPM. The only ones that would prevent the grinding were the non synthetic "dino juice" gear oils. This may not be a problem for some people, but my ZX2 is also my daily driver and driving the car on a cold winter morning when its 20 degrees outside with non synthetic transmission fluid makes shifting feel like Iím trying to stir a jar of molasses. The synthetic gear oils donít have that problem.

On the fall of 2005, my Spec Stage 2 clutch exploded while driving down the road. Because the clutch was in several pieces and no longer worked correctly, it took some force to get the transmission out of gear so that I could push the car. When I took the transmission out of gear, it apparently bent the 3rd-4th gear shift fork. Because of this I had to open up the transmission and replace the shift fork. After opening up the transmission case and getting a look inside, I noticed that the shift forks were exactly the same as the ZX2 and escort sedan shift forks. The ZXTuner transmission shift forks even had the same numbers on them as regular ZX2 shift forks. The rumor going around the ZX2 message boards of stronger shift forks in the ZXTuner transmission is false. They are the same parts.

After driving with the ZXTuner transmission for a while, I noticed a significant drop in highway gas mileage. With the modifications that were on my 2000 ZX2 S/R at the time, I was averaging 37 MPG highway when driving at 65-70 MPH. With the ZXTuner transmission in the car, I was averaging 31 to 33 MPG highway when driving at 65-70 MPH. The ZXTuner is advertise ad having a 0.69 5th gear ratio so that it doesnít hurt your gas mileage much and it acts like a 6 speed without 5th gear since the first 4 gars are for performance and the 5th is like the 6th gear of a 6 speed, geared for good highway mileage. I started to pay attention to my RPM at various speeds in 5th gear. At 70 MPH in 5th gear, the engine was turning 3500 RPM with the ZXTuner transmission and tuned about 3000 RPM with the stock transmission. At 80 MPH, the engine was turning about 4000 RPM with the ZXTuner transmission and tuned about 3500 RPM with the stock transmission. If the ZXTuner transmission had the advertised 0.69 5th gear ratio, it should turn a hair over 3100 RPM at 70 MPH and just under 3600 RPM at 80 MPH. I knew something wasnít right and kept an eye on the RPM at various speeds in 5th gear. I did the math and figured out that my ZXTuner transmission came with a 0.78 5th gear ratio and not the advertised 0.69 5th gear ratio. As a side note, when I had the Escort sedan gear ratios in my car, at 70 MPH, the engine turned about 2700 RPM and at 80 MPH the engine turned about 3100 RPM. At 65 MPH on a relatively level highway, I could get 41 to 44 MPG with that tall overall 5th gear ratio from the escort sedan. However performance suffered a bit. The sedanís 3rd gear overall ratio is about the same as the ZXTuner transmissionís 4th gear overall ratio.

Because of the excessive RPM and poor gas mileage, I started a search for what Mazda or Ford car that uses that transmission came with a 0.69 5th gear. So far, I havenít found a single one sold in the U.S., Canada, Japan, Australia, or Europe that has a 0.69 5th gear ratio. I did find several automatic transmission cars and minivans sold my Mazda that had a 0.69 top gear ratio. However, it doesnít seem like their gears are compatible with the ZX2/Escape transmission. So the best 5th gear ratio I can find is the 0.72(actually 0.717, but I rounded it up) 5th gear ratio. With a 0.72 5th gear ratio in the ZXTuner transmission, the engine should turn about 3250 RPM at 70 MPH and 3700 RPM at 80 MPH.

After figuring out that my Transmission didnít have the right 5th gear, I started paying more attention to the other gears to see if they had the same ratios that were advertised. Rob at ZXTuner said that the ZXTuner transmission has the ZX2 gear ratios for 1st and 2nd gear and the escape ratios for 3rd and 4th gear. I found out that I have the Ford escape gear ratios for 1st and 2nd gear instead of the ZX2 gear ratios. A call to Rob at ZXTuner solved that for me. He said the transmission shop that builds the transmissions uses the Escape parts for 1st and 2nd gear if they donít have any good ZX2 parts.

I did some math to figure out how much this changes things and it correlated with my real world observations about engine RPM and vehicle speed in 1st and 2nd gear. With the ZX2 first gear with the ZXTuner transmission the maximum engine speed for my ZX2 at 7400 RPM should be a little under 35 MPH, however it is actually 31 MPH with my Escape 1st gear. With the ZX2 Second gear with the ZXTuner transmission the maximum engine speed for my ZX2 at 7400 RPM should be a hair less than 63 MPH, however it is actually 55 MPH with my Escape 2nd gear. This seems to hurt me a lot in autocross racing. I have to shift a lot more often than I should between 2nd and 3rd gear.

Not everyone has a ZX2 modified to the extent of mine, so Iíll give some examples for those that obey the stock redline of 6500 RPM. With the ZX2 first gear with the ZXTuner transmission the maximum engine speed of 6500 RPM should be a little less than 32 MPH, however it is actually 27 MPH with my Escape 1st gear. With the ZX2 Second gear with the ZXTuner transmission the maximum speed of 6500 RPM should be a hair 55 MPH, however it is actually 49 MPH with my Escape 2nd gear. For those of you that autocross, this can really hinder your times because you will spend a lot more time shifting. Also, since both the 1st and second gears are lower, it makes the spacing between 2nd and 3rd larger. Instead of the engine turning about 4600 RPM after the shift to third at 6500 RPM, it turns about 4100 RPM. Looking at ZX2 dynos will show you the difference in power and the power lost by that extra 500 RPM drop.

Here is a table comparing the ZXTuner transmission's advertised 5th gear ratio with the stock 5th gear ratios and also the gear ratio that mine was delivered with. Notice how many more RPM mine turns at highway speeds than the advertised 0.69 5th gear ratio(marked in red). Also you can see the difference in RPM when compared to a stock ZX2 transmission for the advertised ratio and the delivered ratio.

After my experiences with it, if I knew then what I knew now, would I have bought a ZXTuner transmission? Probably not. I could have gone to my local salvage yard and got the transmission out of a wrecked escape or tribute and changed the 5th gear and had the driveshaft shop make me a set of custom axles for it. I would have ended up with the same thing for hundreds of dollars less. For what I spent on the ZXTuner transmission and axles, I could have brought a spare ZX2 transmission and a escape/tribute transmission purchased at a salvage yard to a local transmission shop and had them build a transmission with the ZX2 1st and 2nd gear ratios, the Escape 4th and 5th gear ratios and a 0.72:1 5th gear ratio. Then had the driveshaft shop make me a set of custom axles for it. Another thing I could have done was to buy a Quaife LSD for a Mazda version of our transmission and install it in the ZX2 transmission and then have axles made for it. It may have ended up costing a few hundred dollars more, but I wouldnít have poor gas mileage, mismatched gear ratios, and I would have something I could trust to work properly and not leak fluids all over. In the end, I just feel like I wasted $1700.