i recently replaced the tranny on my best friends 97 gp supercharged car. after talking to a respected tranny shop, they told us the non supercharged tranny would work fine, but the gear ratios are different, so we got one. after putting it in, and note this for anyone who reads this....the passanger side half shafts are different from the supercharged tranny to the non supercharged ones. easily fixed by getting a half shaft from a non supercharged one.(the splines are bigger in the supercharged models)

nonetheless. it shifts hard and downshifts too quickly. its throwing a code P0742A, tranny control circuit stuck on. keep in mind also on the tranny change, the torque converter on the non supercharged tranny did not match up with the flex plate mounting holes, so we had to use the torque converter on the old tranny.

any ideas about the code? should i change the modules over from the old tranny to the new one? is the pcm noticing the different control modules on the non supercharged tranny and giving a fault code. im familiar with cars, obviously or i wwould never attempt a tranny change on this car, but im not too familiar with the comp systems controling everything. obviously the guy at the tranny shop left out some important details.

just to give important info on tranny change for this vehicle again, please note..

1- halfshaft on pass side will have to be replaced if going from a tranny from a supercharged model to a non supercharged model.

2- torque converter does not match, either need to use the supercharged one in the non supercharged one, or replace the flex plate to the appropriate one.

3- undetermined shifting problem and trouble codes as stated above.

any insight would be greatly appreciated, because i do not want to spend another 6 hours swapping out something...thanks

i recently replaced the tranny on my best friends 97 gp supercharged car. after talking to a respected tranny shop, they told us the non supercharged tranny would work fine, but the gear ratios are different, so we got one. after putting it in, and note this for anyone who reads this....the passanger side half shafts are different from the supercharged tranny to the non supercharged ones. easily fixed by getting a half shaft from a non supercharged one.(the splines are bigger in the supercharged models)

nonetheless. it shifts hard and downshifts too quickly. its throwing a code P0742A, tranny control circuit stuck on. keep in mind also on the tranny change, the torque converter on the non supercharged tranny did not match up with the flex plate mounting holes, so we had to use the torque converter on the old tranny.

any ideas about the code? should i change the modules over from the old tranny to the new one? is the pcm noticing the different control modules on the non supercharged tranny and giving a fault code. im familiar with cars, obviously or i wwould never attempt a tranny change on this car, but im not too familiar with the comp systems controling everything. obviously the guy at the tranny shop left out some important details.

just to give important info on tranny change for this vehicle again, please note..

1- halfshaft on pass side will have to be replaced if going from a tranny from a supercharged model to a non supercharged model.

2- torque converter does not match, either need to use the supercharged one in the non supercharged one, or replace the flex plate to the appropriate one.

3- undetermined shifting problem and trouble codes as stated above.

any insight would be greatly appreciated, because i do not want to spend another 6 hours swapping out something...thanks

The guy at the tranny shop left out a lot of details. DTC error code P0742 meaning the torque convertor is stuck in the on position would explain the hard shifting.

To the best of my knowledge you should have gone with a 4T65E-HD tranny from a GTP or similar GM model. The shift points are programmed differently via the ECU/PCM. The HD tranny has a different pressure control solenoid (PCS) valve and control circuit. The HD tranny runs higher line pressure to compensate for the additional hp and torque, etc.

I believe you have a conflict in programming between your GTP ECU/PCM and the regular 4T65E tranny.


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Thrasher CAI, DHP v1.0 ECU,
3.25 SC pulley, CAIT GMAF, Hi-Flow CAT,
u-bend delete, 160 TS, TB spacer,
MSD 8.5mm wires, Autolite 104 Spark Plugs,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials

bnaylor3400 is absolutely right. The guy at the tranny shop gave you some bad information and cost you a lot of extra effort. The transmission you put in the car will probably not hold up very long and you will be replacing it again in the near future. The best practice it to replace the transmission with one of an identical model to the one you removed as it will eliminate both computer problems, durability issues and performance problems.

Years ago when the transmissions were not controlled by the computer you could swap just about any transmission that would bolt to the engine into a car and not have too many issues. Today that is just not the case. I hope the transmission holds up but at least you have experience in changing transmissions.

Well thats just news i didnt want to hear. its bad enough, we got bad information about the tranny. he called another tranny guy yesterday and they told him the ecm is going through a learning process due to the different tranny, but im not buying that. hes got a 1 year warranty on the tranny, i told him im not replacing it unless his wife drops it. thats one job i didnt enjoy doing, and i love wrenching. first of all, dropping a sub frame is never fun, and its even worse getting it back up.....lol also i had the new tranny in the car with the sub frame back in, and i noticed the torque converter did not line up with the flywheel. thats when i started pounding the beers. i wish he still had his 85 f150, it was much easier dropping a motor and tranny in that...lol anyway thanks for the help!