hi new here hopeing to get some help

i got a 2003 2500hd 6.0 with the 4l80e sencond gear went out in it so i bought a used transmission out of a totaled 2006 with 85,000 miles on it for $350 got it in all forward gears work great but revears didnt work. after hours of thinking and trouble shooting we un plugged the main grey plug and got reverse. my question is now where do i ook to fix this problem?

it must be an electrical issue but what do i look for or what do i change?

also the new trans mission had 2 sensors on the side and my old one only had 1 so only the front sensor is plugged in is this an issue? as far as i read theback one is a speed sensor with i have plugged in on the tail shaft so i didnt think it would matter.

 

so ive found out it has to be a diffrence in the internal wiring from a local transmission shop but they wouldnt clue me in on how to fix.

has any one ever installed a newer 4l80e in a older truck like this where they had to re wire anything r had this same problem?

do i need to change out selinoids?
wire harnes?
valve body?

i still have my old transmissin that i can take parts off of if need be to make it work.

 

03-06 should be the same. Is your truck 2 or 4wheel drive?

 

its 4 wheel drive local shops are telling me the internal wiring is diffrent.
all i know is when the grey plug is plugged in i have no reverse i un plug it and i have reverse

 

03 and up are the same. 02 uses a different EPC solenoid and internal harness but the case plug is the same and it will work with the newer truck fine. For example, I am running a 03 4l80e with a 02 internal harness as the older style EPC is more reliable with my 04 truck.

 

ok so does anyone have a clue why reverse only works when i unplug that grey plug?

 

Does the rpm flare when you put it reverse (slip)? When yoy unplug the transmission its operating at maxium line pressure. that might be enough to apply the reverse band if its worn. Try driving it down a hill in manual first if there is no engine breaking then its the band. Reverse is a manual function in the valve body. If your old transmission had reverse and the new one doesn't then the trans you installed is broken. The local shop is full of **** the wiring is not different. I rebuild these on a regular basis.

 

no the rpm doesnt change at all when i put it in reverse then only thing i have noticed is the truck will not roll forward at all if in reverse. and yes it does do the engine breaking down hill. i pulled the pan again today just to inspect everything and it all looks good no broke wires and yes the wireing is the same as my old trans the shop is full of ****. so not my auestion is if i disconect the pressure switch or whatever you call it (so i have reverse) could i drive it this way till my other trans is rebuilt or would this hurt somehing? and if so what wire would i disconect on the outside of the trans?

 

Thanks for chiming in Mark.

 

If you try to move the vehicle in reverse does it feel like its in gear or in neutral?