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What do they do exactly and why do people install them?
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The torque converter in front of your 4R100 automagic tranny has a computer-controlled clutch to lock or unlock the torque converter to the tranny. When the torque converter is locked, then the engine crankshaft is tied almost directly to the driveshaft that drives the rear wheels. But with the torque converter unlocked, the only thing that ties the engine to the rear end is a bucketfull of ATF inside the torque converter, so the pickup can almost free-wheel down the mountain as that ATF sloshes around inside the torque converter.
The PCM in most '99-up PSDs will lock the torque converter at about 37 MPH when accelerating, and unlock it at about 37 MPH when slowing down. But it will also unlock the torque converter any time you apply the brakes. Some PCM codes will relock the PCM after you get off the brakes if you are still going more than 37 MPH. Others won't relock the torque converter unless you mash on the go pedal while going at least 37 MPH.
For towing, you want that torque converter locked any time you are coming down the mountain with a heavy trailer pushing on you. Even if you apply the brakes to slow down a bit, you want that torque converter to stay locked. The locked torque converter combined with the coast clutch in the tranny will give you at least some engine braking. And if you have an exhaust brake, then the locked torque converter can add a lot of engine braking.
So the main purpose of a torque converter lockup switch is to assist with braking by increasing engine braking when being pushed down the mountain by a heavy trailer. The only caveat is you must remember to unlock it every time before your speed drops below about 20 MPH. Else it would be like coming to a stop in a stick shifter without mashing the clutch. Not a good. /ubbthreads/images/graemlins/crazy.gif
With my PCM code and a really-good coast clutch in my tranny, I don't need an exhaust brake or a torque converter lockup switch to tow my 8,000-pound 5er all over the USA - including the so-called mountains back east and the real mountains out west. But with a heavier trailer I would. Or with a different PCM code, or with a less-than-perfect 4R100 tranny, I might.
probablecause,
Smokey is right, my trans program will lock the converter at a rather slow speed, but will unlock between 3 and 4 up shift or down shift and you get RPM rise and power loss. I built my own (not difficult) I have 3 LEDs one for Lock Up from the PCM another showing I locked it and the last when the 18K is on. Smokey is right about forgetting to turn off.... /ubbthreads/images/graemlins/biggrin.gif it will kill the engine if you come to a stop with it locked. /ubbthreads/images/graemlins/phoney.gif
My converter doesn't unlock in overdrive when I let of the pedal or touch the brakes. It will coast with the converter locked until a bit under 40mph, and then unlock and downshift to 3rd at the same time. It will also stayed locked in 3rd (until around 30mph) if you have the OD off button enabled. This is VDH2 ecm code. The manual lockup switch would be useful if your computer unlocks your converter anytime you hit the brakes. That would get annoying quick.
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37 MPH when accelerating, and unlock it at about 37 MPH when slowing down
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Not true
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Okay, so what is true?
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Some PCM codes will relock the PCM after you get off the brakes if you are still going more than 37 MPH
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Oh? Which pcm codes would that be?
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I don't know about other PCM codes but my original NVK3 and my current MRT3 will both relock after I brake going down the mountain at over 60 MPH. I know some don't by reading this website for the last 7+ years.
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The locked torque converter combined with the coast clutch in the tranny will give you at least some engine braking
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Might wanna make it clear that you have to have the OD button locked out for this to happen as well.
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Could be. I never tow down the mountain without the OD button locked out. /ubbthreads/images/graemlins/cool.gif I can't imagine anyone being that bad of a driver.
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37 MPH when accelerating, and unlock it at about 37 MPH when slowing down
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Not true
Sure nuf. Well, not totaly. Under acceleration, lockup mph can vary. With my code, UNK1, durring WOT my TC will lock before the 1/2 shift, which is ussually under 37 mph..
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Some PCM codes will relock the PCM after you get off the brakes if you are still going more than 37 MPH
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Oh? Which pcm codes would that be?
Well, UNK1 for starters. Mine does it all the time. As long I am above 37 mph, tap the brakes it unlocks, let er coast and it will re-lock.
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The locked torque converter combined with the coast clutch in the tranny will give you at least some engine braking
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Might wanna make it clear that you have to have the OD button locked out for this to happen as well.
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My converter doesn't unlock in overdrive when I let of the pedal or touch the brakes. ... This is VDH2 ecm code. The manual lockup switch would be useful if your computer unlocks your converter anytime you hit the brakes. That would get annoying quick.
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Those DP tunes on your X-Cal have more than likely changed the way the TC locks and unlocks. Return programming to stock and it would imagine it would unlock when you hit the brakes.
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My converter doesn't unlock in overdrive when I let of the pedal or touch the brakes. ... This is VDH2 ecm code. The manual lockup switch would be useful if your computer unlocks your converter anytime you hit the brakes. That would get annoying quick.
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Those DP tunes on your X-Cal have more than likely changed the way the TC locks and unlocks. Return programming to stock and it would imagine it would unlock when you hit the brakes.
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Even with my stock VDH2 programming it is this way...
And I verified it this morning on the way to work.
As long as I am above 50 mph, it will unlock with a tap of the pedal, and imediately re-lock.
Below 50 it will stay off.
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