4L60E transmission reverse issue?

[68laydout]

05 Avalanche starting to have an issue with reverse. Doesn't do it 100% of th time and seems to do it mostly after the truck is warm. It will start to reverse and then it feels like a transbrake is holding it.

Anyone had this issue before? Thanks, Cory

[clinebarger]

Next time you have this problem shift it in to neutral...If moves forward the forward clutches are staying applied Most likely from a internal crossleak feeding the forward clutches.

[68laydout]

Thanks for the response and I will do that next time it happens. I've read these transmissions have a manual reverse valve body. Could it be something stuck or cross leaking in the valve body? Also read the reverse and low are on the same clutch pack.

I appreciate your response! Cory

[clinebarger]

Originally Posted by 68laydout

Thanks for the response and I will do that next time it happens. I've read these transmissions have a manual reverse valve body. Could it be something stuck or cross leaking in the valve body? Also read the reverse and low are on the same clutch pack.

I appreciate your response! Cory

It has a Manual Valve in the Valve Body, Not your problem. If the forwards are applying in reverse I would suspect a hair-line crack in the Input shaft/drum assembly.
Yes, The low/reverse clutches are applied in Park, Reverse & Manual Low.
Some more info on what happens in reverse.

Reverse
When the gear selector lever is moved to the Reverse (R) position (from the Park position), the following changes occur to the transmissions hydraulic and electrical systems:

Manual Valve
The manual valve moves to the Reverse position and line pressure enters the reverse fluid circuit. As in Park, line pressure also fills the PR (Park/Reverse) fluid circuit. All other fluid circuits are blocked by the manual valve.

Lo and Reverse Clutch
As in Park, PR fluid pressure acts on the outer area of the lo and reverse clutch piston to apply the lo and reverse clutch. Also, Lo/reverse fluid from the lo overrun valve acts on the inner area of the piston to increase the holding capacity of the clutch.

Reverse Input Checkball (#3)
Reverse fluid pressure seats the #3 checkball, flows through orifice #17 and fills the reverse input fluid circuit. This orifice helps control the reverse input clutch apply rate when engine speed is at idle.

Reverse Abuse Valve
Reverse fluid pressure acts on the end of the valve opposite of spring force. At engine speeds above idle, reverse fluid pressure, which is fed by line pressure, increases and moves the valve against spring force (as shown). Reverse fluid can then fill the reverse input fluid circuit through the reverse abuse valve. This bypasses the control of orifice #17 and provides a faster clutch apply.

Boost Valve
Reverse input fluid pressure moves the boost valve against the pressure regulator valve spring. The spring acts on the pressure regulator valve to increase the operating range of line pressure in Reverse. Reverse input fluid also flows through the valve and to the reverse input clutch piston. Remember that torque signal fluid pressure continually acts on the boost valve to control line pressure in response to vehicle operating conditions.

Reverse Input Clutch Piston
Reverse input fluid pressure moves the piston to apply the reverse input clutch plates and obtain Reverse.

Reverse Input Air Bleed Checkball
This ball and capsule is located in the reverse input fluid circuit in the oil pump to provide an air escape when the fluid pressure increases. It also allows air into the circuit to displace the fluid when the clutch releases.

Transmission Fluid Pressure (TFP) Manual Valve Position Switch Assembly
Reverse input fluid pressure closes the normally open reverse switch in the TFP manual valve position switch This signals the PCM that the manual valve is in the Reverse (R) position.

Shift Solenoid Valves (1-2 and 2-3)
Both shift solenoid valves are energized as in the Park range. Signal A and signal B fluids are blocked from exhausting through the shift solenoid valves to maintain fluid pressure in these circuits at the end of the shift valves.

Shift Valves (1-2, 2-3 and 3-4)
Signal A fluid pressure holds the 1-2 shift valve in the downshifted position and the 3-4 shift valve in the upshifted (First and Fourth gear) position. Signal B fluid pressure from the 2-3 shift solenoid valve holds the 2-3 shift valve train in the downshifted position.

[68laydout]

Thanks man. I appreciate you taking the time to do this and I have a much better understanding now. Now I just have to decide if I want to tear it down or let someone else. It's my daily driver so I need to get it right the first time. I've rebuilt t350's and t56's, so I might give it a go. Thanks again! Cory

[68laydout]

Originally Posted by clinebarger

Next time you have this problem shift it in to neutral...If moves forward the forward clutches are staying applied Most likely from a internal crossleak feeding the forward clutches.

It does move forward after shifting to neutral. I'm thinking about buying a rebuilt and just swapping it out. Do you know of a good place to buy a rebuilt here in the DFW?

Thanks, Cory