New to G/A's, Trans swap question [Archive] - Forum


View Full Version : New to G/A's, Trans swap question

06-24-2009, 08:54 PM
Hi everyone, I just bought an 01 SE with a 3.4l and 4t45e. It has relatively low miles (85k). The trans has a shudder on the 1-2 shift on hard accel. It seems to be getting worse so I am going to order a rebuilt unit from a very good tranny shop that dynos everything they sell.

My question is this. Is the 3:29 gears in only the GT cars or the V6 se's as well? If not I would like to put in the lower geared trans for better take off. In theory in should be a plug and play as I cant see how the lower final drive would affect anything else. Of course I am not sure and I need your guys help! Thanks

06-24-2009, 10:11 PM
I believe the SE's had a 3:09 gearing. Not sure if the gearing change would affect the current PCM settings or not.

06-25-2009, 06:39 AM
SE is 3.05, gt is 3.29, everthing bolts up, but youre speedo will be off.

06-25-2009, 11:22 AM
The trans will swap directly in, but you have to have your pcm reprogrammed with the file for a GT or it won't work properly. It's more than just the speedometer and odometer too. When you aren't at full throttle the pcm uses mph and throttle position to determine shift points for up and down shifting instead of using rpm. If the gearing is changed the mph changes relative to rpm and the computer will be shifting at different times than it thinks it is. Basically it will shift all funny.

06-25-2009, 09:35 PM
the speedo gets its signal from the final drive so I cant see how a lower gear ratio would affect it. At least that's what I recall from the last time I swapped one of these trannys.

06-26-2009, 09:57 PM
*welcome* man

WTF is Ft. McMurray?

06-27-2009, 06:30 PM

Its far northern Alberta, Canada. Biggest oil sands reserves in the world up here! Keeps me busy lol

06-28-2009, 04:59 PM
Ah. Cool.. err... Cold.. I guess. lol

Good money though, right.

06-28-2009, 07:55 PM
Yeah in winter in gets bad, but summer is great! 80 degrees from June to September and long days! Sun comes up at 5 am and stays up until 11 pm!

Winter goes from November to march and varies from 14 degrees to -30!!!

Money is probably about as good as you can find in Canada, I make 45 and hour as an automotive mechanic!

07-01-2009, 12:15 PM
the speedo gets its signal from the final drive so I cant see how a lower gear ratio would affect it. At least that's what I recall from the last time I swapped one of these trannys.

Had to wait until I got home from a trip so I could do some research in my manual and make sure this was right, so here it is.

Yes, the vehicle speed sensor gets it's signal off a reluctor ring pressed onto the differential. The thing is, there are two different drive ratios for the differential itself. Both the V6 GT and V6 SE use a 4T45E transmission with the code MN5, but the GT uses a model code MXJ and the SE uses a WXJ. I couldn't find anything in my manual as to whether they use the same reluctor ring or if they use ones with a different number of teeth... but it doesn't matter. They still use a different sun gear for a different final drive ratio, which combined with a specific drive sprocket and chain configuration, makes the effective final drive ratio.

The pcm is programmed for a specific output range from the VSS to correspond to a given mph based on a set number of pulses per mile that is calculated based on the effective final drive and tire size. The faster the pulses, the faster the mph. Change the final drive or the tire size and the speedometer and odometer will be off, because the IPC gets it's data directly from the pcm, and the number of pulses no longer matches how far or fast you are actually going. If you have a tuner like me, you can change the pulses per mile to account for tire size or gearing changes.

If you change the final drive without reprogramming, at the worst you may gets a SVS light because the pcm will set a DTC if it does not see the expected signal range from the VSS versus the input shaft speed sensor (ISS) and/or wheel speed sensors. At the least you will get some funny feeling shifting and transmission operation. The WXJ and MXJ transmissions use different programming in the pcm and shift at different mph vs throttle percentages (another thing you can tweak with a tuner). The pcm also uses both the ISS and VSS signals to control shift points and patterns, torque converter lock apply and release, TCC slip calculation, and shift line pressures.

Bottom line is, you cannot just swap out a trans from an SE or GT into the opposite car without reprogramming the pcm and expect it to work right.