Diagnosing no reverse 4l80e
Diagnosing no reverse 4l80e Just picked up an 02 GMC with a **** ton of miles and trans issues. Tranny has no reverse and seems to have little power or not in 1st gear when put in drive.
I’m automatic-retarded so reaseach says it could be VSS giving a reading the truck is moving when it’s not. Which won’t let reverse engage and throw it into another gear besides 1st when put into drive.
Could be reverse servo pin possibly? Or more internally?
Is unplugging the front VSS good enough to rule it out as bad or should I swap the front and rear sensors and try? What else should I check after that? Line pressure?
I’m automatic-retarded so reaseach says it could be VSS giving a reading the truck is moving when it’s not. Which won’t let reverse engage and throw it into another gear besides 1st when put into drive.
Could be reverse servo pin possibly? Or more internally?
Is unplugging the front VSS good enough to rule it out as bad or should I swap the front and rear sensors and try? What else should I check after that? Line pressure?
Thought I’d try a fluid and filter change but I’ve got a feeling I’ll just be pissing in the wind. Hell I might try it anyways. I’ve always kinda wanted to try an automatic rebuild and it looks like I might get my chance.
TECH Fanatic
Joined: Jan 2015
Posts: 1,114
Likes: 33
From: Fort Worth, Texas
Reverse is purely hydraulic, No electronic failure will cause you to lose reverse. Fitzall makes a rear band apply pin extension that may fix your no reverse issue temporarily (If the rear band is worn)......Common cause with the loss of reverse but you still have 3rd gear.
It could also be a broken band servo piston. Common on '97 & up 4L80E's.
Weak Forward apply could be from smoked Forward Frictions, Common on high mileage 4L80E's from the Input Shaft getting into the Forward Drum sealing ring lands.
It could also be a broken band servo piston. Common on '97 & up 4L80E's.
Weak Forward apply could be from smoked Forward Frictions, Common on high mileage 4L80E's from the Input Shaft getting into the Forward Drum sealing ring lands.
Thanks cline, the truck has 341k miles on it and no telling if the trans is original now. Any good trans shops in Ft worth? Id like to tear into it but if it has that many miles it may be a complete waste.
