Hi guys! So, I have G35 2007 AWD with Biturbo GTM kit installed. Currently, my config is 450 wheels HP and 500 N-M (370 ft-lb). Transmission is the really weak part of the car - I don't if the car was tuned bad or it just can't handle current torque but it slips very often when I press full acceleration, then wait for a moment, then gear 'could' be changed and it will ride normally. In manual mode the situation is bad too - there are sometimes kicks (or slip, I'm not sure) from AT. I have an additional cooler installed and constantly checking AT temp using Launch and it never went over 110°C (230°F). Several days ago when I ride in 'half-pedal acceleration' mode my tranny slipped again and then I got a check engine. I read errors and they were: P1574 (ASCD Vehicle Speed Sensor), C1130(Engine Signal 1), C1143(Steering Angle Sensor Circuit), U1002 and the last but not the least P0735 5th. Gear Malfunction. And from that moment I don't have 5th gear at all. I tried to clear all DTC (I have Launch CReader which can do it for the engine, AT, ABS, SRS) and tried to drive very calmly shifting manually from 1 to 5th gear. So I 'can' switch to 5th gear (I can see number 5 on the dashboard) BUT there is no 'connection' between engine and transmission. I mean that engine RPM grows but the car doesn't respond on acceleration. (I hope that I described it clear).
Now my car is parked and I think about what to do next. This is 4th repair of transmission on this car and even some details were ordered from Level10 service (I don't know what exactly but know that TransGo shift kit is installed in valve body). The 'fun' part that I did the full repair 800km ago (all frictions and broken hard parts were replaced, torque converter also was refurbished) and drive pretty carefully this period.
So, now I'm stuck what to do... The problem is that I live in Ukraine and there is even no such thing as change/update firmware in transmission even at official dealers (trust me, I called a lot of guys already). I found the guy from another city who suggested that I swap my transmission to QX56 because it has 528 N-M in stock and transmission can handle this torque, but I'm not sure if it is possible. I even found transmission gear ratios in service manuals for G35 and QX56 AT and they look pretty same:

G35 gear ratio

QX56 gear ratio

So any advices would be appreciated! Maybe ECU tuning is killing my transmission all the time? Is it possible?

P.S. There is also option to swap to MT from 350Z but I don't want to lose AWD and I consider this as the lastest option.

 

It's hard to say whats going on without data logging the transmission while tuning pulls. The ecu has to be tuned just right or the trans will not shift correctly and burn things up. One question, do you have a shop tuning the car that has experience with the 5AT? To make a Titan / Armada / QX series transmission work you will need a shop to custom build it. The input shaft spacing and bell house swap will require cutting and machine work and driveshafts will need modifying too, in other words it's not a bolt up deal.

 

Unfortunately, I didn't find any service at this moment who will do this custom work. I know only that service who suggested this swap, but they are located far away from me. The serviceman told me that we will use the bell house from current transmission. But what most important, he said that QX56 has different planetary hardware and more 'thicker' friction disks. Is that true?

> The ecu has to be tuned just right or the trans will not shift correctly and burn things up.
The ECU is tuned terribly IMHO:
* engine idle RPM changes all the time even when the car is warmed up
* I have Innovate MTX-L air/fuel ratio gauge installed and measurement could be a maximum value (22.4) when I just roll after acceleration
And I don't even know what was used for tuning because I bought this car when it was tuned already. I will try to get more information about how it was tuned but the question is still relevant - is it worth swap to QX56? Does it really have more strong hardware than G35?

 

Sounds like the car just hasn't been tuned correctly. If it has already been acting like that and driven under boost for awhile it's probably toast and needs a rebuild. The QX56/Armada/Titan 4x4 transmission is a lot tougher. Has steel baskets and more area for clutch packs, billet steel 5 gear planetary instead of aluminum and 4 planetary and the internals weigh over 10lbs more. The big problem is that the input shaft / input drum is different than our car uses and cannot be swapped between. If you use the QX56 torque converter you will have to modify the VQ bell house to fit the large torque converter, modify trans mount and lengthen / shorten your driveshafts. That's just to make the front side of the transmission work, the output shaft will need to be changed to work with AWD instead of 4X4 transfer case too. It's a lot of work to get a 4x4 transmission to work in a awd but it is better.

 

Thanks, I also think I need to retune it after transmission rebuild. And what about RE5R05A from Nissan Pathfinder 4.0L (VQ40D) engine? I've been told that it is also stronger than G35 transmission. Is it true? They (G35 and Pathfinder) have the same gear ratio and stall torque ratio. Maybe swap to Pathfinder AT if it is 'stronger'?

 

If I remember correctly there are only 2 different internal ratios. I haven't got into the 4.0l trans but would guess they are built the same as the other 4x4 transmissions. I'm pretty sure they used beefed up internals on any vehicle that was capable of 4x4 and towing.

 

We are actually getting started on a turbo 08' G35x right now and will be pushing the stock RE5 AWD trans with just a shift kit so I'll try to pop in here and let you know our findings. After the stock burns up we are going to rebuild it and fix the weak spots and repeat.....

 

Wow, great news! I would be very appreciated if you share your experience! I will try to find this RE5R05A from Pathfinder and examine it. Hope it would not cost a lot here in Ukraine...
P.S. As I understand the reason why transmission 'slips' after turbo kit is that TCM expects some predefined torque but gets greater values and doesn't know what to do... So in theory, if we can rebuild hardware AND modify AT firmware based on power/torque of the engine then it solves all problems. Maybe I write obvious things or maybe I wrong at all .

 

Here are my measurements from dyno stand, just in case (I don't know if they are relevant at this moment, but this is all I have from the previous owner). My boost is 1.15 Bar (16.67 PSI).

 

If you are using Uprev it would be interesting to go over the tune file. When you change to larger injectors is where the tranny load tables get screwed up and need a lot of work to shift correctly. Manual trans cars are a lot easier to tune.