quick question about a transmission [Archive] - GrandAmGT.com Forum

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icecats87
02-21-2011, 08:21 PM
I have a 2001 grand am gt with a 4t45e tranny it has the 3.29 gear ratio i got a free transmission from a member on here its a 4t45e but a 3.15 gear ratio, will this cause any problems at all besides a little lack of performance, will it hook up perfectly and will the car run? thanks for for help

AaronGTR
02-21-2011, 08:34 PM
It will hook up to the car fine, and it should run, but your shifting might act funny.

icecats87
02-21-2011, 08:45 PM
It will hook up to the car fine, and it should run, but your shifting might act funny.

How funny do you think? my professor was doing calculations and was saying something like a 3% **** rate difference or something he said it wouldnt really be noticeable just wanted to ask if anyone else had a thought because i almost have it out of the car and didnt want it to not work after all the time it took to drop it

AleroB888
02-21-2011, 09:18 PM
I thought you were going to swap out the diff :)

There are other parameters in the PCM that are different, that might prevent it from running well. I tried a GAGT PCM in my '99 Alero, and after putting about 10 miles on it, the shifting became harder and it just did not act right. The PCMs can be reflashed, possibly a dealership could do that and retain your VIN# and OS for the vehicle.

Now I do have a 2001 GrandAm V6 PCM that you can try if you want. Only way to test it is install it, do the relearn, and see if it works.

icecats87
02-21-2011, 09:30 PM
I thought you were going to swap out the diff :)

There are other parameters in the PCM that are different, that might prevent it from running well. I tried a GAGT PCM in my '99 Alero, and after putting about 10 miles on it, the shifting became harder and it just did not act right. The PCMs can be reflashed, possibly a dealership could do that and retain your VIN# and OS for the vehicle.

Now I do have a 2001 GrandAm V6 PCM that you can try if you want. Only way to test it is install it, do the relearn, and see if it works.

Was going to do the diff swap but my teacher said it wasn't worth tearing a completely good tranny apart, then said the 3.15 ratio wouldnt make that much of a difference so i guess ill tell my teacher that and ill probably swap the diff out

XtremeGaGt00
02-21-2011, 09:32 PM
like aaron said, it may shift weird, because the pcm has a set gear ratio its programmed for..and your changing that..may even set a code for incorrect gear ratio..so the worst that happens is you swap it, and get a reprogram for that transmission code.

edit..if you swap diffs. have fun with alllllll them parts x|

icecats87
02-21-2011, 09:35 PM
alright i have the PCM from mpracing so would i be able to just send it back to get re programmed for 3.15 ratio?

XtremeGaGt00
02-21-2011, 09:38 PM
alright i have the PCM from mpracing so would i be able to just send it back to get re programmed for 3.15 ratio?

i dont see why he couldnt do that

icecats87
02-21-2011, 09:43 PM
i dont see why he couldnt do that

And then it wouldn't "shift funny" with it programmed to 3.15 correct?

XtremeGaGt00
02-21-2011, 09:45 PM
i wouldnt think so

AaronGTR
02-22-2011, 04:40 PM
Yeah, your teacher is probably thinking that it won't make a noticeable difference in acceleration... it will, but not a huge difference. The thing is, he probably has NO IDEA how the computers in these cars work. It is a completely electronically controlled transmission. Sometimes it shifts based on MPH and throttle position, sometimes based on engine rpm, depending on how hard you are driving. Messing with the gearing when it is programmed for a 3.29 FDR is why I said it might shift funny. Either use the correct diff, or get the PCM reprogrammed to properly work with the new one.