Newbie Question: Torque Converter Lock up

[Barra]

I was reading back posts the other day and came across "Bad fuel economy ??? " which has a discussion of torque converter locking. My question is do all the torque converters in these trucks lock, or only some?

Cheers!
Barra

[moondoggie]

Good Day!

My 84 Sub (not listed below, long since gone) had a 700R4. I think the only AT's used behind 6.2's & 6.5's are 700R4 & 4L80-E, & both have locking torque converters. (More informed members will correct this info if it's wrong, I'm sure.)

Blessings!

Brian Johnson, #5044

[HowieE]

Yes they all lock.
Once you are traveling above 50+, depending on your truck, the convertor should be lock. You can tell by watching the tack as you approach 50. You should see about a 200 RPM drop as the convertor locks. At speeds abouve 55 you should be able to step down lightly on the throttle and NOT see a junp in RPMs. The RPM should go up as road speed goes up but should not lead the road speed. If you step on it all the way at a spped above 55 you should see the tack jump 4-500 RPMs as the convertor unlocks and drop back once the computer calls for lockup.

[Phil Holmen]

HowieE has stated correctly about the torque converter lockup but I have always found it easier to test when driving at about 60 mph tap the brake with your left foot while holding the accelertor steady. You should see the tach jump about 200 rpm. If so, your torque convertor is working.

[ssybert]

I have noticed this... When I'm getting on it picking up speed, The RPM's and speed will both be climbing then, all of a sudden, the speed will continue to climb, but the RPM's will drop a couple hundred, then start climbing again. It's a different fealing than a gear shift and I never knew what it was doing.

What does this "lccking" mean/do? I'm sure it's something it's supposed to do, but why does it do it?

[markrinker]

A locking torque converter has the ability to go 1:1 (no slip) at a predetermined fluid line pressure supplied by the transmission, thus 'locking' itself between engine output at the flywheel and transmission input shaft.

Below that line pressure, there is slip at the converter, where some engine torque is dissipated as heat into the transmission fluid, rather than twist into the transmission input shaft.

Think of it as what you do manually, when slowly releasing the clutch to allow your engine to take on the load gradually without stalling.