When do you lock your convertor?

In my 05 it locks at 10mph, well before the 1-2 shift. It has about 400 1/4 mile passes doing it that way. Both the input and output shafts are Opies fat shafts, as well as other strengthing mods done by Ultimate Transmission. The lockup is controlled by a pressure switch.

On my 02 I lock it at the top end of 2nd gear. It has taller gears, and doesn't have the hp and torque that the 05 does. It also has a 47re valve body and doesn't lock in first.

As a recommendation, don't do the lockup and shift to close together. The govenor pressure solenoid may not be able to handle both events at the same time.

Paul
 
I played around with lock-up last weekend at the track with my 15 second daily driver. Even at just the 300-350 HP range, the sooner I locked it up, the quicker it went even though it sounded like it was bogging the motor out and almost snuffing out the HX35. I lost 2 tenths by waiting till half-way through 2nd gear to hit lock-up.

On my 95' Junker Drag Truck, I turn on the lock-up switch at the line and as the truck is making the 1-2 gear shift, it simultaneously locks up the torque converter.
 
Lots of good info! Thanks!

I figured locking off the line from a stop would be hard on parts but it is what I belive I read Smittys truck does. I guess it would be similar to just dropping the clutch. Would locking it at the top of first be less RPM change than in the bottom of second? That to me, would be what is hard on the shafts is a larger RPM difference from input speed and engine speed.
 
This is where the argument is bound to happen, but... Locking the converter when there is a large difference between the engine rpm, and the input shaft rpm, will put a large amount of stress on parts. Doing that lockup in a higher gear, will increase the stress. For an analogy (probably a really bad one), but if you strike something with a hammer that is hard to move, it will apply more force, then if you hit somthing with a hammer, that is easy to move. If you are in first gear then the input shaft has a mechanical advantage over the output shaft. When the converter locks up, it is easier for the input shaft to accelerate. In 4th it is much harder for the input shaft to accelerate.

If you lockup the converter too close to the shift, then the lockup is trying to accelerate the output shaft, as well as the shift is trying to accelerate it. And at least one is probably happening close to peak torque in the engine.

Lock it, let the engine recover, and then shift it. Or visa-versa.

Paul
 
On my truck, when the converter locks, line pressure momentarily drops. When it shifts gears, line pressure momentarily drops. If you lock up at the same instant as the gear shift, it softens lock-up because the dual momentary drop in line pressure causes the torque converter to lock-up softer as well as lets the 2nd gear band slip a little more. For long converter and transmission friction life, this isn't the best method, but for long shaft life and less shock-load on hard parts, this seems to be the best method.

In my experience, not nearly as much as Paul or others with several thousand 1/4 mile passes under their belt, the sooner I lock the converter, the quicker (Lower ET) it runs as long as you don't snuff out the charger. When I was running a single GT4294, locking the converter in 2nd would snuff out the charger and cause it to run slower, I had to wait till the top of second gear to lock-up.
 
On my 47RH I have the TPV fixed wide open. This isn't recommended for daily drivers. But I have driven it on the street with no ill effects.
 
dont mean to derail guys but question here for ya..would i benefit at all with a lock up switch even though i have a tight t/q say 91%...thanks guys...
 
mulisha said:
dont mean to derail guys but question here for ya..would i benefit at all with a lock up switch even though i have a tight t/q say 91%...thanks guys...
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Yep, I'm sure it would shave at least .2 seconds off of your current best ET.
 
Lock up after shifting to 2 here! Some.interesting points on this thread.
 
My converter locks as soon as I hit 2nd, but I've got it set on the PCS to read off 3 different parameter.
 
Craig_C said:
Just wanted to see when most people are locking the convertors?

Anyone lock it up off the line? When I do my trans swap, was thinking of using a momentary contact on the brake pedal so that when the brake is released the convertor locks, right off the line.
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:umno::badidea: ok, back in the day.........which has been a long time for me, but when we first built the truck we set the converter to lock up as soon as my foot came off the brake. I am pretty sure i wired it to the brake switch. Anyway, we were probably only around 1100 horsepower at the time and lets just say all of the planetaries exploded into shrapnel when we did this, we never even moved 5 feet. I would advise against it but at the same time if you could make it work i believe it could make for some fast passes. It's been a long time ago since i tried this, maybe 8 years. Anyway, carry on.
 
paulb said:
This is where the argument is bound to happen, but... Locking the converter when there is a large difference between the engine rpm, and the input shaft rpm, will put a large amount of stress on parts. Doing that lockup in a higher gear, will increase the stress. For an analogy (probably a really bad one), but if you strike something with a hammer that is hard to move, it will apply more force, then if you hit somthing with a hammer, that is easy to move. If you are in first gear then the input shaft has a mechanical advantage over the output shaft. When the converter locks up, it is easier for the input shaft to accelerate. In 4th it is much harder for the input shaft to accelerate.

If you lockup the converter too close to the shift, then the lockup is trying to accelerate the output shaft, as well as the shift is trying to accelerate it. And at least one is probably happening close to peak torque in the engine.

Lock it, let the engine recover, and then shift it. Or visa-versa.

Paul
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Interesting point, but locking it up in first gear you bang the input shaft for all of the other shifts also. Also that locked 3rd to 4th shift is wicked.
 
i do know when in 1st locked the WFO shift into 2nd is violent....3rd and 4th are not quite as bad but still rough
 
I lock mine in the top of second, any sooner and it just spins the rear tires, being 2wd and on proxes with no traction bars.
 
Ether Man said:
:umno::badidea: ok, back in the day.........which has been a long time for me, but when we first built the truck we set the converter to lock up as soon as my foot came off the brake. I am pretty sure i wired it to the brake switch. Anyway, we were probably only around 1100 horsepower at the time and lets just say all of the planetaries exploded into shrapnel when we did this, we never even moved 5 feet. I would advise against it but at the same time if you could make it work i believe it could make for some fast passes. It's been a long time ago since i tried this, maybe 8 years. Anyway, carry on.
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ONLY 1100. Wish I only had that much powerLOL
 
Now that we've covered locking the converter, the next question is:

When do you shift into overdrive? As in, at what RPM?

My answer: the faster I shift into overdrive, the quicker the truck runs as long as it doesn't snuff out the atmosphere charger (HT4B).

Other people's experiences will be different but I've tried hitting OD at 2400 rpm, 2500 rpm, 2600 rpm, 2700 rpm, 2800 rpm, 2900 rpm, 3000 rpm, 3100 rpm, 3200 rpm, and 3300 rpm.

My truck's current sweet spot seems to be 2550 to 2600 rpm. Any sooner and it momentarily bogs and I lose 1/2 of one tenth or (.050) If I shift at 2700 rpm, I lose about (.050). If I shift at 3100 rpm, I lose (.20) seconds. At 3300, I loose a solid (.30) seconds.

I'm sure a lot of this has to do with the power band of the motor based on injection pump, injectors, timing, cam, and turbo setup. But on my mostly stock motor, 2550 rpm is the hot ticket for low ET.
 
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DieselWrencher said:
On my 47RH I have the TPV fixed wide open. This isn't recommended for daily drivers. But I have driven it on the street with no ill effects.
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x2 on my 89. I just lift to shift so it doesn't bang so hard.

I'll never lock a converter at the bottom of a gear if I can help it, too hard on them. I think that's why so many 9 second diesels are eating converters is that they are locking them at the bottom of a gear when the slip rate is 50% versus at the top of a gear when it may be 30% or less.
 
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