Torque converter lockup
- Thread starter Larry
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Toy-Man
New member
Larry,
It's hard for me to explain, if I am not clear perhaps someone else will drop by and do a better job of it than me.
When cruising on a level road the at 50+ MPH the torque converter should be in locked mode. Now slowly give it some gas but not enough to downshift. As you do this, you should notice the engine increase RPM in step with the truck speed. As you continue to increase pressure on the accelarator at a certain point, engine RPM will increase with no real associated speed increase from the truck. Your torque convertor is now unlocked and you can notice slippage in the convertor at this point. The transmmison in this state seems "shushy". When it unlocks , it can easily be mistaken for a downshift but it's not quite as drastic. Eaes off on the gas a bit, let the truck get up to spped and the convertor will once again lock giving the sensation of a slight upshift.
Watching the tach while doing this will help.
Hope this helps
-TM-
It's hard for me to explain, if I am not clear perhaps someone else will drop by and do a better job of it than me.
When cruising on a level road the at 50+ MPH the torque converter should be in locked mode. Now slowly give it some gas but not enough to downshift. As you do this, you should notice the engine increase RPM in step with the truck speed. As you continue to increase pressure on the accelarator at a certain point, engine RPM will increase with no real associated speed increase from the truck. Your torque convertor is now unlocked and you can notice slippage in the convertor at this point. The transmmison in this state seems "shushy". When it unlocks , it can easily be mistaken for a downshift but it's not quite as drastic. Eaes off on the gas a bit, let the truck get up to spped and the convertor will once again lock giving the sensation of a slight upshift.
Watching the tach while doing this will help.
Hope this helps
-TM-
Last edited:
Thanks Toy-man, I'll try it. It makes sense. Another thing about the transmission, if I hit the gas a little harder than normal, while in 'Drive' it appears to be sluggish. If I hold the transmission in third and hit the gas a little harder than normal, it really responds and jumps, it feels like the engine is more directly connected to the gas pedal. You change speed, up and down in a way that is very direct. In Drive it's like there is a lag beween moving the gas pedal down or back.
TechWrench
Senior Member
Toy-Man said:
I will have to check my manual for the specs, but I am pretty sure that the converter should lock-up at lower speeds as long as the load (acceleration) is low enough.
Hitman
New member
toyoboy said:
I think you're a little confused.... when the torque converter locks up, it eliminates the slip between the impeller and the turbine. Therefore, the torque converter lockup causes the impeller and turbine to rotate at the same rpm, effectively "locking" them up together.
Hitman
New member
toyoboy said:
Not really.... you said that the torque converter only locks up when the impeller and turbine are turning the same rpm.
If that was the case, then there would be no need to "lock" the torque converter, because the rpm would already match between the impeller and turbine.
It is the locking action that causes the impeller and turbine to rotate at the same rpm, not the other way around.
TechWrench
Senior Member
toyoboy said:
This is not necessarily true. Most lock-up circuits are designed to allow a certain amount of torque load before releasing lock-up. Under 'normal' acceleration, the converter can achieve lock-up once the proper speed has been reached, depending on the gear and operating temp. Slight changes in speed, either acceleration or deceleration won't normally affect lock-up, but once the set load point has been reached, lock-up is released until it drops below the set point.
TSP-MIKE
New member
The torque converter will lock up at around 50mph and the engine should be at the normal operating temperature. Drive normally and lightly push the brakes a bit with your left foot (You must keep your right foot on the gas), not enought to slow the car down but to turn on the brake lights. You should be able to see your RPM jump about 500rpms. That would be your torque converter unlocking.
Mike
Mike
Does anyone have any trouble with the torque converter staying unlocked when it shouldn't?
I do a lot of driving on west Texas I-10 (75 mph speed limit), and I like to use the cruise control. Many times I have caught the tach reading about 200 RPM too high. If I turn off cruise control and then reset it to the same speed, the revs then stay normal until I get tired of watching the tach. Then, maybe 50 miles later I'll notice the revs have jumped again.
It looks like the converter might be unlocking on an uphill grade, and then not relocking when the road is level again.
I do a lot of driving on west Texas I-10 (75 mph speed limit), and I like to use the cruise control. Many times I have caught the tach reading about 200 RPM too high. If I turn off cruise control and then reset it to the same speed, the revs then stay normal until I get tired of watching the tach. Then, maybe 50 miles later I'll notice the revs have jumped again.
It looks like the converter might be unlocking on an uphill grade, and then not relocking when the road is level again.
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