Project G37S Transmission Upgrade part 2

Since we didn’t have an expert level of automatic transmission building, we opted to have Level 10 assemble a complete bulletproof transmission for our car. For $4,998 plus a core charge of $800 they will rebuild a transmission as listed previously with new clutches, their upgraded valve body and an upgraded torque converter. Trusting a pro shop in the business of doing this sort of work for 47 years with all the specialty tools seemed like a much better option than using an unknown shop to take the parts and perform the work on a complicated 7-speed automatic transmission. 

With the driveshaft and exhaust out of the way Howard gets ready to get the old transmission out.

Once the order was placed it was a surprisingly quick one week turn around for Level 10 to get the trans built and sent out to us.  Their team was great answering all our questions regarding build time, the install and what needed to be done to get the car tuned properly. When I asked about the tune for the new transmission the folks at Level 10 asked who’s tune we currently had on our car and we replied Omar from UpRev.  “Oh, Omar he’s the best, you’re in good hands,” they said.

Howard removes the transmission mount from our stock transmission to swap over to the bulletproof Level 10 unit.

Removing the transmission was surprisingly short work.  Howard loosened the rear mufflers and removed the X-pipe section of the exhaust. Then the driveshaft came out, the transmission bolts were loosened and a jack was placed under the transmission and it was removed from the car.  Howard swapped over the transmission mount and we re-installed the new transmission. 

Despite some knowledge passed around on the internet, it is possible to both fill an empty transmission like our rebuilt unit or replace the fluid in your 7 speed AT without a Nissan Consult scan tool. The filling process took about 10.5 quarts of Nissan S-Matic transmission fluid. We followed Level 10’s instructions of filling, waiting till fluid dripped out of the fill hole, starting the car letting it run, adding more fluid, starting running the car in gear, filling again and finishing.

Martin establishes a couple of baseline runs on the car. Then Omar from UpRev remotes into our laptop with the UpRev software and begins tuning our car.

The lockup on the torque converter and the line pressure is controlled by the ECU so our transmission break-in process actually took place on the MotoIQ dyno. Omar from UpRev remoted into our laptop at the MotoIQ Garage and we strapped the G37 down to our shop’s Superflow dyno and awaited for our GO from Omar. After a couple of shakedown runs to ensure the transmission was working normally we got a baseline run on the car’s power. Martin joked around with me that the Superflow dyno at the MotoIQ Garahe is a heartbreaker, because the power numbers read low compared to a Dynojet. When we last left off at UpRev on their dynojet, with tuning we ended up with a Max HP reading of 311.99 and Torque of 256.45.  On the Superflow Max HP was 252.9 and 202 Torque. So heartbreaking it was, but it was expected and we had our new baseline.

Resetting the baseline is extremely important when using different dynos. Without the proper points of reference the comparison data is useless. Remember, it’s not about the peak numbers, it’s about the delta.

On the bottom right you can see our communication with Omar. He goes through the fueling and timing tables to add more power and finishes off working on the driveability and highway cruising.

Watching all the numbers fly by during the runs, it’s clear Omar knows a ton about these cars by the messages he was sending over.  “Your fuel pump may be weak. How much gas do you have in the car? Your oil temps are running hot, you should look into adding an aftermarket oil cooler.”  When we were back in Texas Omar made a similar comment about the fueling so we’ll have to address that in the future, as well as adding that oil cooler. With oil temps reaching up to 239 degrees we’d only get a few runs in on the dyno before we’d have to shut it down for 30 minutes and try again.


  1. Surprised there is no love for this. I totaled my G37S at a track day and it still bums me out. But the transmission was a very weak link. I imagine this upgrade would really wake it up. How is the transmission for daily driving?

  2. Daily driving is almost like stock. There’s definitely a difference when the transmission is cold versus warm; best described as a small stumble that happens between gear changes. Once warm though this completely goes away. When decelerating and the car downshifts the engine braking is definitely more pronounced. Not to repeat what was already put in the article but gear changes now really shove the car forward where before shifts really felt soggy. None of this takes away from the car it only adds to the grins and this upgrade appears to be a must for forced induction.

    I’m sorry to read about your car. Hopefully your replacement is just as fun or you took it as an opportunity to try something different. There are a lot of cool cars out there I’d like to try. If I had to do it over again maybe I’d try a Golf R or a Q50 Redsport or a 335. Price was the deterrent to all those cars 4 years ago when I bought the G37S so bang for the buck it’s hard to beat the Z or G37 as a GT car. I don’t need to daily drive the car anymore so something a little more extreme like a used Camaro ZL1 or a Corvette come to mind as does a Cayman or Boxter or BMW M car but the price-point is obviously higher and so are the repair costs which is why I’m still very into what I have.

    1. Hi Aaron, I have a g37s sedan that I have turned into a time attack track car. I definetly feel the transmission is the weak link. I really love the paddle shifters over a manual. Would you recommend this upgrade for the track? Does it make the car faster or just feel faster?

      1. @Tom,

        Sorry I don’t have timed verification for you on the quicker shifting. I didn’t take the car to the track before to see how the car performed to then have a measurement after. My main concern was removing the weak link in the powertrain when we add more power. I would definitely recommend this transmission for the track with the note that you should add both an oil cooler and a transmission cooler. Stay tuned and you might see an article on that soon ;). The 370Z and the G37 both seem to do a pretty good job of running the fluids hot.

        I really do wish you could experience the Level10 transmission yourself beforehand to see how much better it is.

  3. Ah man, I wonder how the good Dr. is doing. I loved watching the progress of his SE-R build with the transmission and turbo kit.

  4. @Khiem, well I feel the same way about your S2k. This one has been fun as it has gone from daily driver to weekend toy. Hopefully, like you we’ll get to add a lot more power.

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