4L80E concerns

[AceRock]

I have a 2004 Chevy Silverado 2500 LD (similar to a 1500 HD) with the 6.0 liter motor and 4L80E trans. Truck has 40K miles. Does anyone know if this transmission has a locking torque converter? If so then wouldnt the RPM stay constant at highway crusing? I am slightly concerned because lately I notice that the engine speed is higher at 70mph then it used to be. This is not by much however(about 250rpm). Just wondering what this might be all about.

[mmmikkke]

You should be able to notice the lock-up at about 50 mph (as long as you're lightly accelerating using maybe 1/8 throttle). Above that speed, you should be able to go from cruising throttle to light acceleration and back without changing the engine rpm. Try both below 40 (unlocked), and above 50 (locked), and you should see a difference.

[Trouttrooper]

Find a stretch of highway and do a constant light-moderate acceleration. You should be able to feel the converter lock up (kinda like a "5th" gear shift). Watch the tach as well and you should see it drop a little.

 

Another way to test is once your crusing at around 60mph don't move your gas pedal, manually shift the truck from D to 3. Give it a couple seconds then shift back into D. It should immediatly go back into overdrive and about 2 seconds later it should lock up the converter (watch the tach and listen to the engine).

[Bish]

Another way to check for lockup is to drive down the highway at constant speed. Tap the brake lightly and the converter should unlock and then lock again and you SHOULD be able to feel it and see it in the tach.

[gave20]

At 60mph with a 3:73 rear you should have 2000rpm's cruising and around 2500rpm's at 70.

[AceRock]

Thanks for all the advice on how to check for converter lock-up. I checked it this morning on my way to work and it was locking up Thank goodness too since it is just out of warranty! I used to pull a fairly heavy preasure washing trailer with this truck when it was brand new and now use it to tow my boat and jet ski and dont want this thing giving me problems out in the desert. I do have 3:73s and have 2500 rpms at 75 mph so I guess I shouldnt be complaining if you have that engine speed at 70 gave.