Quote:
Originally Posted by BINZ
Looked through the threads and could not find a link.
Anyone here have an issue with the AT trans heating up and changing RPM shifting ?
Thanks  |
I don't think reasonable trans temps affect the D-mode shift points in normal operation, no. Those should be determined basically by engine speed, vehicle speed, current gear, throttle position, and engine torque. I believe higher engine coolant temps will pull some timing on the engine and reduce available torque, so you could see some change to shift points in that case, maybe.
The best heat test I've done so far is 4x ~80-90 second SCCA solo laps spaced a few minutes apart, in 101F heat outside. Those were done in M-mode staying in 2nd gear all the way through, mostly at 4K+ RPM the whole time and pretty much constantly either accelerating or engine braking. I didn't have a trans cooler at the time, and nothing unusual happened to indicate any kind of trans malfunction.
In any case though, D-mode always makes poor decisions. If you care about which RPM you change gears at, use M-mode.
The 7AT does have a failure mode if the trans temp goes above the preset safety limit. I've never seen it happen in practice, but this is the description from the service manual:
To summarize above, basically if your TCM exceeds 145C for 2 minutes straight, or 150C even momentarily, the TCM will tell the ECU to limit your throttle position pretty dramatically, and it will go back to normal once the fluid gets back down to 140C *and* the car comes down to a 3mph roll or slower.
Note - this is the temp of the TCM (electronics control module on the side of the transmission housing). It would be affected by fluid temp, but it's not exactly the same as the fluid temp.