Hello everyone. I have a 2000 GMC Jimmy 4.3l V6 with the 4L60E transmission. I bought it with the sun shell splines stripped, and attempted to rebuild the transmission myself.

I used the upgraded sonnax smart shell and put everything back together with new clutches, steels and gaskets.
I have a weird issue after rebuilding it.
Drive, 321 and neutral all move the vehicle forwards.
Reverse doesn't move it anywhere and it wouldn't rev past 2k in "reverse".

I am not really sure what the issue could be and would really like some help on determining some possible issues that would cause these symptoms? Could it be something simple or do I definitely have to take it apart again? I can and probably will have to pull the transmission back out to fix the issue, im just worried I won't find anything obviously wrong and want to know where to start.
Maybe I can work down a list of simpler things before I commit to another rebuild? Thank you and any information is appreciated.

 

Same issue. Truck sat for about 6 months. I had a horrible time replacing a transmission line that rotted out. Finally got it fixed no leaks and now no reverse. In neutral it moves forward but eventually it will not move unless put in drive. Drive 1 moves really slow. Thinking of draining the transmission fluid, flushing it, and refilling. My understanding is it’s a stuck spring or clutch plate where in reverse they cancel out and it won’t move. Not sure if there are any easy fixes.

 

I'd also remove the transmission oil pan and have a thorough look for corrosion on the solenoids.
At that time also replace the oil filter if the transmission looks o.k.

 

I can help --- mebbee --- but you're there and I'm not and unless I can put my hands on it --- well ---> this IS the internet - right?

It's prolly take it out again time --- but I'll try to give you list of the usual suspects --- not in order, but as they occur to me .... .

Something's happened to the Reverse Clutch and I'm sure you've played the solenoid game already.

Since that's been done <right?> - it may be an internal leak in the Reverse Apply Circuit or a busted sunshell snapring or a cross-cut axial seal.

Did you use the scarf-cut Teflon or the one-piece versions? Either can be damaged, but the scarf-cuts tend to stick up and get their noses cut off when you slide the stator into place. --- and that caught me in my younger days --- it looked so "natural" yet I did this a few times until I broke down and bought the installer and swaging tools by OTC.

Did you replace the boost valve or get it dirty?

Dirt is the biggest killer of transmission repairs --- well, that and lack of experience or not wanting to go all the way and fix it completely the first time.

DIY builders can fail to keep the job and workspace surgically clean --- it's that bad.