1996 C1500, Trans seems to shift late when hot, AC on

[jasons]

My sons truck, 1996 C1500, 5.0 seems like it shifts late or maybe it's not locking the TC, when hot. Monitoring coolant temps with my OBD reader, we're seeing around 185 degrees it seems to shift normal. When it starts to get over 200, we see this shifting issue. I think it's most obvious when leaving a stoplight so I'm not sure if it's isolated to a 1-2 shift. My son thinks it's all shifts. Typically the AC is on too which I don't know how that's a factor other than obviously adding heat to the system. Also we put in a new VSS with no change. I've looked through the items in this thread and I'm not sure I see anything that leaps out.

4L60E Messed up? Help Within

Written by Dok Erik Von Broski This will be of some help: 1. Slow, slipping or no reverse: low/reverse clutches are worn out, fluid leak in the reverse apply circuit, or broken sun shell. It is possible to remedy a fluid problem by removing the check ball from its cage in the case in...

www.gmt400.com

Also, checked the fluid level and it's spot on.

 

[NickTransmissions]

My sons truck, 1996 C1500, 5.0 seems like it shifts late or maybe it's not locking the TC, when hot. Monitoring coolant temps with my OBD reader, we're seeing around 185 degrees it seems to shift normal. When it starts to get over 200, we see this shifting issue. I think it's most obvious when leaving a stoplight so I'm not sure if it's isolated to a 1-2 shift. My son thinks it's all shifts. Typically the AC is on too which I don't know how that's a factor other than obviously adding heat to the system. Also we put in a new VSS with no change. I've looked through the items in this thread and I'm not sure I see anything that leaps out.

4L60E Messed up? Help Within

Written by Dok Erik Von Broski This will be of some help: 1. Slow, slipping or no reverse: low/reverse clutches are worn out, fluid leak in the reverse apply circuit, or broken sun shell. It is possible to remedy a fluid problem by removing the check ball from its cage in the case in...

www.gmt400.com

Also, checked the fluid level and it's spot on.

More than likely you have excessive wear in the valve body, pump (boost and/or pressure regulator valve) and/or applied elements so higher than normal line pressure rise is required to fully stroke valves and/or deliver sufficient clamping force to fully apply the clutch and/or band.

I'd do a line pressure test at idle and stall once the trans warms up to 200+ or so and let us know the readings. Harsh 1-2 shift can be one or more things, including worn TCC regulator/isolator valve in the VB (known issue with the 95+ units), worn/poorly sealing 1-2 acc piston, worn rear stator bushing in the pump, torque converter, excessive band clearance, broken 1-2 accumulator spring, etc.

How many miles on the transmission?

 

[jasons]

More than likely you have excessive wear in the valve body, pump (boost and/or pressure regulator valve) and/or applied elements so higher than normal line pressure rise is required to fully stroke valves and/or deliver sufficient clamping force to fully apply the clutch and/or band.

I'd do a line pressure test at idle and stall once the trans warms up to 200+ or so and let us know the readings. Harsh 1-2 shift can be one or more things, including worn TCC regulator/isolator valve in the VB (known issue with the 95+ units), worn/poorly sealing 1-2 acc piston, worn rear stator bushing in the pump, torque converter, excessive band clearance, broken 1-2 accumulator spring, etc.

How many miles on the transmission?

I've never done a line pressure test. Any good "how to" resources for that?

Truck has like 160k on it, I have no reason to believe the trans has less than that.

 

[NickTransmissions]

I've never done a line pressure test. Any good "how to" resources for that?

Truck has like 160k on it, I have no reason to believe the trans has less than that.

Here you go (it also covers 700R4 TV cable adjustment which is not applicable so you can ignore...The line pressure test info is on page 6.

At 160k it's in the twilight years/miles so I'd start planning for a rebuild sooner rather than later.