Thread: 99 GT Tranny 4th gear gone

4th gear finally went out in my 99 n/a gt. I'm getting it rebuilt and want the chain ratio changed from 35/35 to 37/33 to get an overall ratio of 2.93. Anyone know how this will affect the economy of the car?

Yes..you will see lower rpm. You will need a pcm reprogram and maybe tweaks to keep it from bogging.

Originally Posted by BillBoost37

Yes..you will see lower rpm. You will need a pcm reprogram and maybe tweaks to keep it from bogging.

What kind of tweaks?

Well.. you are NA, so your motor isn't an all out power monster and your shift speeds are based on 3.29 gearing. This gearing keeps your rpm higher which means you'd have more power. By swapping the gearset you will lower rpm at those same speeds, this causes bogging because the motor wasn't designed to hold 4th gear uphill at 42mph at 1100 rpm. The motor simply doesn't have the power and it'll bog.

You would want to tweak your shift points in order to allow a downshift earlier and or shift into gear at a slightly higher rpm.