Transmission Hops when hot

[The Salmon]

My 1999 Yukon runs great after an engine rebuild. I have a long drive to work each day and they are hard miles. Seems as I come to the end of my journey and it is hot, the tranny bangs a little hard between first and second. Is there a tranny thermostat on my 5.7 vortec 4WD? I know I'm due for a fluid and filter change, but I think it is more than that. Any help???

 

[Marky Dissod]

Automatic Transmission Fluid Protectant - Lubegard

www.lubegard.com

PLATINUM ATF Protectant - Lubegard

www.lubegard.com

COMPLETE Full Synthetic ATF - Lubegard

www.lubegard.com

Before you get any of those, might want to consider a used ATF analysis,
might give a better answer than we can.

That said, there are some hard parts that wear out, loosening clearances.
When they do, stuff like that can start to happen.

Do you have an external ATF cooler? Not part of the radiator?
If not, would only help to have one.

 

[Joseph Garcia]

@NickTransmissions

 

[NickTransmissions]

My 1999 Yukon runs great after an engine rebuild. I have a long drive to work each day and they are hard miles. Seems as I come to the end of my journey and it is hot, the tranny bangs a little hard between first and second. Is there a tranny thermostat on my 5.7 vortec 4WD? I know I'm due for a fluid and filter change, but I think it is more than that. Any help???

It's likely that your torque converter clutch regulator/isolator valve(s) and their respective bore in the valve body is worn. Your pump's main pressure regulator valve may also be wearing, requiring higher circuit pressure to stroke those respective valves to complete the gear transition.

The only real way to diagnose is to drop the transmission, take the valve body and stator support to a Sonnax or similar vacuum tester and have both tested for wear.

Any DTCs such as P1870?

 

[Eman85]

Have it scanned for codes, common for the problem Nick mentioned. I have done a fix with the Fitzall kit that changes TCC from pulse width modulated to just on/off TCC. I've also had one that had been fixed with the Sonnax kit but it needed a new torque converter. The Lubegard might buy some time but time will run out.