Hello to all, I am new here, my name is Brian and I am in need of some help if possible. My dad is a transmission mechanic, and he recently had a customer bring him a 2000 pontiac Grand Prix GTP , supercharged 3.8. It needed a new transmission,but they wanted a used one put it in, instead of having him rebuild it, so that's what he did,got a used one from the salvage and put in it. Come to find out,it is out of a NON GTP,so it has a 3.29 ratio, where as the stock GTP trans had a 2.93 ratio.
The trans works,but the shifts are weird,it kinda just "pecks" on the shift,but has every gear and doesn't slip or anything,but the timing seems off a little also, but after my research and finding they are different ratio, the PCM probably needs a reflash it seems. The only change they did was put the HD differential off the old trans, onto the trans they put in it. As far as I've researched,it seems the GTP has a 3.29 differential, combined with a 37 drive and 33 driven chain gear set,which would make it a 2.93 final drive, (37÷33=1.121 ratio) (3.29÷1.121= 2.93-1 final drive). He put the HD 3.29 differential onto the trans we put in it, but the trans we put in it is not and HD, so it will have a 35 drive and 35 driven gear and chain set,which would be a 3.29 ratio. (35÷35=1:1) (3.29 differential÷1 = 3.29-1 final drive).
We are sure this is the reason for the weird shifts,because the PCM in the GTP is programmed for the stock 2.93 final drive shift points, instead of the now 3.29 final drive. Can someone here reflash the computer for us to work for the 3.29 ratio?
We could take the whole transmission back out and change out the gears and chain to the ones out of the trans that came out of it,but that would be alot of work! A computer reflash would be much easier for us. Can someone here do that for us if we took the computer out and send it to ya? Nothing else in the stock tune needs to be changed,just the final drive ratio from the stock 2.93 to work with the "now" 3.29. Can somebody help please?
Thanks in advance, Brian
