What exactly does the torque converter lockup switch do?

[diesel_dave]

I've been messing with the position of this switch such that it always reads continuity and also such that it always reads open regardless of pedal position. I have noticed no difference in the behavior of the truck whatsoever. Let off the throttle and RPMs drop down to idle while rolling. Should it stay locked up? Been awhile since I drove a non-electric car and I don't remember normal behavior.

What does this thing actually do?

 

[simp5782]

When a torque converter locks up, it inherently lowers rpm's because the slippage that happens in the converter is minimized, hence "locked".

 

[diesel_dave]

When a torque converter locks up, it inherently lowers rpm's because the slippage that happens in the converter is minimized, hence "locked".

Yes I'm tracking that aspect of it. I just don't understand what this switch does? Pressing the brake unlocks the converter but it seems to unlock any time I let off the throttle or the engine RPM wouldn't be at idle when rolling 50 mph. What is it supposed to be doing? I imagine holding rpm until some speed where it unlocks so the engine doesn't stall.

 

[simp5782]

Yes I'm tracking that aspect of it. I just don't understand what this switch does? Pressing the brake unlocks the converter but it seems to unlock any time I let off the throttle or the engine RPM wouldn't be at idle when rolling 50 mph. What is it supposed to be doing? I imagine holding rpm until some speed where it unlocks so the engine doesn't stall.

Shouldn't lock until 45mph or more.

You can get a controller and lock it whenever you want.

At what speed does the torque converter lock in a 4l80e trans

I just got my humvee with a 6.5 turbo and a 4L80e trans--Shifts 2-4 are smooth but I cannot feel the torque converter lock up--Around what speed does it lock--Thanks George

www.steelsoldiers.com

 

[diesel_dave]

Shouldn't lock until 45mph or more.

You can get a controller and lock it whenever you want.

At what speed does the torque converter lock in a 4l80e trans

I just got my humvee with a 6.5 turbo and a 4L80e trans--Shifts 2-4 are smooth but I cannot feel the torque converter lock up--Around what speed does it lock--Thanks George

www.steelsoldiers.com

I took it up to 70 for the first time last night. As soon as I let off the throttle, RPMs drop to idle. Is that normal or should it hold and provide some engine braking?

 

[simp5782]

Bad solenoid will unlock itself while cruising and coasting and then relock when throttle is applied. I think there are 2? I'm assuming this is a 4L80. You could drop the pan and make sure the harness isn't rubbing.

I took it up to 70 for the first time last night. As soon as I let off the throttle, RPMs drop to idle. Is that normal or should it hold and provide some engine braking?

 

[diesel_dave]

I guess my follow up question is why do we need to unlock the torque converter when pressing the brake if it's going to unlock when it gets back down to slow speeds anyway? Essentially, my question is, is it a big deal if my torque converter switch doesn't do anything for whatever reason?

 

[MattNC]

If the TCC was locked and didn’t unlock with you hitting the brakes you’d fight the engine until you got below the speed where it unlocks or if it downshifts.

 

[Mogman]

Matt is correct, the switch is to insure the TC UNLOCKS when you hit the brakes

 

[diesel_dave]

I'm pretty sure it's unlocking as soon as I let off the throttle or it wouldn't be going to idle. Unless I'm missing something obvious?

 

[Mogman]

I did use the word insure as in backup.

 

[TOBASH]

Would you use a switch like that when towing a heavy load?

 

[Hummermark]

I posted this same question as my m1113 (new m1113 stright from the production line,not restored not built from parts privately)does this was told is normal.

 

[Retiredwarhorses]

To test your TCC lockup, drive the truck down the road at 50mph, with your left foot, tap the brake pedal while keeping your right foot on the accelerator, upon tapping the brake, the rpm’s should spike u…

 

[diesel_dave]

To test your TCC lockup, drive the truck down the road at 50mph, with your left foot, tap the brake pedal while keeping your right foot on the accelerator, upon tapping the brake, the rpm’s should spike u…

Is it bad if it doesn't do this? My TCC does lock up fine but doesn't unlock when I press the brake because the switch isn't working for whatever reason. It does unlock when I let off the throttle though so I'm not sure what purpose the brake switch serves since I won't be braking and pressing the throttle at the same time.

 

[Retiredwarhorses]

Is it bad if it doesn't do this? My TCC does lock up fine but doesn't unlock when I press the brake because the switch isn't working for whatever reason. It does unlock when I let off the throttle though so I'm not sure what purpose the brake switch serves since I won't be braking and pressing the throttle at the same time.

The switch can be bad, out of adjustment, but your TCC does not unlock just because you take your foot off the throttle.
Also, your TCM will generate a DTC if it’s either stuck locked, or stuck unlocked…pull codes from the TCM.
you missed the point of my post, I pointed out the proper method to “test” your TCC while driving…

 

[diesel_dave]

The switch can be bad, out of adjustment, but your TCC does not unlock just because you take your foot off the throttle.
Also, your TCM will generate a DTC if it’s either stuck locked, or stuck unlocked…pull codes from the TCM.
you missed the point of my post, I pointed out the proper method to “test” your TCC while driving…

When I let off the throttle and RPMs drop to idle while driving 60 mph, is that the torque converter unlocking? I don't see how it would be possible to do that with the torque converter locked. My trans light is not illuminated if that matters. My TCC absolutely is locking but I am trying to figure out the negative effect of a broken switch because so far I haven't been able to figure that out.

 

[Retiredwarhorses]

When I let off the throttle and RPMs drop to idle while driving 60 mph, is that the torque converter unlocking? I don't see how it would be possible to do that with the torque converter locked. My trans light is not illuminated if that matters. My TCC absolutely is locking but I am trying to figure out the negative effect of a broken switch because so far I haven't been able to figure that out.

That’s all normal behavior, your RPM’s won’t rise, you need to understand that the TCM gets input from TPS, CPS, TISS, TOSS…that’s why you keep your foot on the gas pedal and hit the brake pedal.
The TCM knows by the fact you removed your foot off the gas via the TPS.
You don’t have an illuminated trans lamp for the DTC

 

[Retiredwarhorses]

FYI, every automatic trans works the same way…so a google search on TCC will result in hundreds of responses.

 

[diesel_dave]

That’s all normal behavior, your RPM’s won’t rise, you need to understand that the TCM gets input from TPS, CPS, TISS, TOSS…that’s why you keep your foot on the gas pedal and hit the brake pedal.
The TCM knows by the fact you removed your foot off the gas via the TPS.
You don’t have an illuminated trans lamp for the DTC

What real world situation is pressing the brake and the throttle at highway speeds simulating though? Why would I need to disengage the TCC while pressing the throttle while also simultaneously pressing the brake? Sorry, I'm not trying to be difficult, just trying to understand what possible purpose this test serves. Right now it does not do this but there seems to be no adverse effects that I can discern.