4L80E trans twerk???

[Baszboy]

98 K2500, 4L80E, 5.7, Truck shows 291k miles, trans unknown mileage.

Just got this truck on the road last month. Bought it with a blown engine, replaced it and have been driving it since.
Noticed an interesting problem with it.
Truck shifts fine, all shifts are smooth and solid, no slip or funny noises. However when the outside temp is above 90degrees and you put some miles on the truck during this heat. When you make a full stop and are sitting at a light the rear of the truck twerks? Like you have the AC on and the compressor kicks on and bogs the engine, thats the only way to describe it. Feels like something is kicking in or out and you can feel it when it does this. Its intermittent when it does this, once or twice when sitting at a light, sometimes more or not at all till the next light. A few times just after the twerk I have pulled over and checked the fluid level, normal, nothing smells hot. Yesterday it did the twerk at a light so I just raised the RPM's while sitting on the brake pedal, not much maybe 150 rpm and the twerk quit.
Kind of irritating feeling it and have no clue as to whats going on??

Under 90 degrees outside and you can drive it all day and no twerk!
Perplexed on this?

 

[andy396]

My first guess would be the torque converter is locking up. It happens when there is low fluid flow caused by one or several of the valves like the line to lube valve. The reverse boost valve is known to wear as well. If the trans has that many miles on it, probably not a bad idea to go through the whole thing, but you could start with rebuilding the pump and valve body.

Here’s a good explanation:


https://www.sonnax.com/tech_resourc...in-the-pump-pr-converter-cooler-lube-circuits

 

[L29Sub]

Install a trans temp guage (or read the ECM for same) and see how hot it's running. A broken clutch plate will do that. Low pack. Does it do the same in any other gear selection?
Or, it has a kit installed and something is not quite right. Trying to engage.

Sent from my SM-G965U using Tapatalk

 

[Baszboy]

Install a trans temp guage (or read the ECM for same) and see how hot it's running. A broken clutch plate will do that. Low pack. Does it do the same in any other gear selection?
Or, it has a kit installed and something is not quite right. Trying to engage.

Sent from my SM-G965U using Tapatalk

Have not tried it in any other gear other than drive, when our weather gets hot again I will try it in other selections and see what happens.