About a year ago my truck suddenly decided to idle rough when warm, but goes away as soon as I hit the throttle, so I figured it was no big deal. Then about a month and a half ago the tranny (4L80E) decided to go out without any warning (drove 10 miles sat for 2 hours then no reverse or 4th gear or lock up). Got a reman from autozone since the company they deal with dyno tests them before they are shipped. $1600 later I am noticing that trans temps are much higher, 180° empty compared to 140° with my last trans, and it only has a prominent shift at WOT otherwise at mid throttle it slips about 2 seconds before it catches the next gear. Also cant slow down by down shifting and TCC unlocks as soon as I lut off the accelerator.
Maby the issues are linked?
I have replaced the brake light switch(before trans went out) and the temp sensor on the crossover yesterday.
Any in put? maby accelerator position sensor?

 

4l80e's dont have engine braking so the downshifting thing is normal. TCC is also supposed to unlock at zero throttle input. It sounds to me like your cooler is restricted. I work at a trans shop, you seriously have to flush those things after trans failures they will hold air pressure with the other line off. If it is shifting too soft drop the pan and take a torx bit to the back of the pressure control solenoid and turn it clockwise a 1/8 - 1/4 turn.

 

Also make sure your cooler runs through the radiator first and through the aux cooler 2nd. I've seen a trans shop flip them and caused higher heat.

Trying to compression brake on a 4l80 will decrease its life quickly.

 

I will flush the lines again, already double checked the flow direction through the coolers. I'm going to pick up a filter kit and fluid even though the trans only has about 200miles on it I'd rather be safe, which solenoid do I need to tighten up? Is it the one on the front of the valve body?

 

to be fair i kept a eye on my trans temp today and i got 180 too after a day of driving, as long as its not over engine temp there is no reason to panic. yea the pcs solenoid is not the pair on the rear, it should be towards the front of the trans. I believe its a t-25.

 

If its slipping shifts might be a good idea to go a 1/2 turn, but you need to be cautious. could turn into a monster real quick.

 

I'm putting it back together now, went just shy of 1/4 turn just to be safe. All I have left is flushing the coolers. Thanks for the input.

 

Good luck, let us know.

Mine ran 180 with the factory cooler and if you are driving in town alot you won't get enough air flow to really utilize the aux cooler.

 

First test drive went great, shifted alot quicker and harder. The temp got up to 165 but very slowly, I'll know exactly how good it does going to work tomorrow. The new trans came with a new aftermarket cooler which I mounted below the radiator with its own fan after the temp situation started so if the Arizona heat is too much for the fan I may move it back.
Thanks a ton for the info and quick responses.

 

good luck