TQ lock-up

[CDyksman]

TC lock-up

Can someone tell me what happens when the Torque converter locks? Also what is the purpose of it locking, and when does it lock/un-lock? Thanks.

 

[DerekK]

Can someone tell me what happens when the Torque converter locks? Also what is the purpose of it locking, and when does it lock/un-lock? Thanks.

If I understand your question correctly, I think this is the answer, but I'm no expert. The torque converter is between the transmision and the motor. It has internal fins in opposing direction with fluid between the two sets of fins. The motor turns one set of fins until the fluid fights against the opposing set utill the momentum causes the drivetrain to move. This is adjusted by the degree of the fin's angle against each other and the consistancy of the fluid. Torque converters are like a fuse in your drive train to act as an automatic clutch. You might be confusing that with your real question. The transmission also has a set of internal clutches that overide the torque converter - usually in third gear for towing purposes, or performance depending on the mods in your transmission. And those you feel when you are hard on the gas and you get that mid third gear tug. You can cause them to lock up sooner if you use the tow-haul mode on your shifter, but I have been told that they will release if you stomp your gas to the floor, then the torque converter takes over to relieve the strain on your transmission, but if you ease into the gas and slowly push to about two third of the way down they stay hooked up and you really feel the pull. Hence the poo of your factory torque converter and why the aftermarket has a lot of replacements. You lose a lot of pull with the factory converter for the sake of the blue hair comfort of not jerking you around during hard excelleration shifts.



But again, I'm no expert, and I will most likely be corrected soon if Im wrong.

hope that helps.

 

[JEstes]

I'll add something to that. I'm pretty new to the Dodge/Cummins world, but not to cars in general.



This is a fairly poor analogy, but a tourque coverter is like two box fans stuck together. One side is moving fluid/air, and the other side is being spun by the fluid/air. Since there is no direct mechanical link, the fan that's being driven spins slower than the one that's doing the driving. That means there is some wasted energy.



Like Derek said, your TQ acts like an automatic clutch. At lower speeds, it is unlocked, or slipping. Much like the box fans, the TQ will slip since it has a 'soft' fluid link as opposed to a 'hard' mechanical link. This slipping allows your engine to idle while stopped, and also allows your transmission to shift without damaging things. At higher speeds, your TQ will engage clutches and create a solid ('hard') link between itself and the transmission. The engine/transmission are now directly linked together. At this point, the TQ is no longer slipping. This is what is referred to as lockup.



Now that it is locked, there are times when it needs to unlock. One of those is slowing down. If the TQ stayed locked, the engine would quit once the vehicle slowed too much or stopped. It also can't be locked for shifting. If it did, the rapid change in gear ratios would destroy transmission parts.



There is a downside. Slipping solves some problems, but creates others. For example, a slipping (unlocked) TQ isn't delivering all of the engine's available HP to the transmission. This slipping also creates excess heat. That's why guys with transmission temp guages notice less transmission temp once the TQ locks up. It's also why guys who tow heavy loads with an automatic have to be pretty careful about pulling with an unlocked TQ. The transmission can get hot in a hurry. So, in an effort to cure these problems, TQ's lockup at certain points as opposed to slipping the whole time.





Anyway, hope this helps!

 

[CDyksman]

Yes, this helps a lot. Thanks a bunch!

 

[KWold]

But isnt a main problem (for modded trucks with autos) that the TC can slip while locked, if too much power if applied. And slipping a locked TC is very hard on the TC in general. Also, after slipping a locked TC, particles from the clutch packs can get into your transmission and start clogging things up, creating more issues (like excess heat, etc) if the particles over whelm (or pass through) the transmission filter.



Just curious.

 

[pwr2tow]

But isnt a main problem (for modded trucks with autos) that the TC can slip while locked, if too much power if applied. And slipping a locked TC is very hard on the TC in general. Also, after slipping a locked TC, particles from the clutch packs can get into your transmission and start clogging things up, creating more issues (like excess heat, etc) if the particles over whelm (or pass through) the transmission filter.

Just curious.

You are correct.
That's why the aftermarket uses more pressure and different clutch material and or more TC clutches to keep the TC from slipping.