At that speed with O/D off my trans temp stays right at 170.

 

With the o/d engaged under the load of a trailer, you're going to have slippage between the impeller and the turbine, which generates madd heat, not to mention shifting in and out of fourth, which generates madd heat too.. add to that tq lock unlock, more heat.. pulling with o/d on is worse than bad, its stupid.. in third, and disengaging o/d, you also don't allow tq to lock.. you turn more rpms, but you don't overload the trans by shifting continuously...

C'Mon Unreg, I'm dying here!!! Is tq lock and stall always the same rpm?

 

No...

 

I didn't ask you... Unreg knows his business, and will understand why I'm asking..

 

well then, guess which finger I'm holding up for you? wise a** behind a keyboard, love your type

 

You're breaking my heart, Nancy... When you grow up and after diligence worthy a scholar, you may know a fraction of what Unreg forgets every day... Just the way it is.. don't like it? Go stick tour nose in a book or two.. flip me off while you're at it if it makes you happy..

This drama is yours alone.. I didn't ask you..

 

There's no room for that around here. Take a quick breather...deep breath and join the conversation. Everyone deserves the same amount of respect.

 

Sure! Sorry for the long delay -- I've been out making sawdust.

No, they're not the same. As you say:

That first paragraph is kinda sorta true. The second is perfectly true.

In the first... lots of guys like to claim to know their stall speed by doing brake stalls (brake stands) but what those really tell you about is braking ability. Others take the peak value shown by a tachometer during a hard launch, but that's flash stall and is only rarely meaningful. Then there's true stall which is what happens when you somehow hold everything behind the converter stationary and mash the throttle wide open, and record the engine RPM at which it runs out of poop. Hopefully that's before things break.

They're different functions that don't (or at least shouldn't) have significant interplay.

Things get interesting at times like these. Fortunately, at least in theory, our PCM's engage and disengage the torque converter clutch with a bit of intelligence and more or less "only lock while cruising" if everything is working properly. Working properly doesn't seem to be the norm, from all I've read here. (Have I mentioned how much I like my Mega Viper?)

Tough question! For a highway driven truck, which is all I'm talking about here, a 2500RPM stall is usually way too high. It's always too high for a working truck that hauls heavy loads around.

The goal is to use torque multiplication mode only to get the vehicle moving, and then to stay in coupling mode the rest of the time. If you're relying upon torque multiplication to maintain speed you're just chewing through fuel to make destructive heat, and really do need higher gear ratio behind or more power in front rather than higher stall in the middle.

When you're just cruising along unladen, so running in coupling mode, stall speed is irrelevant. When you pull out on the two lane to pass that pokey big rig, the foot headed for the floor forces (should force) a downshift and as soon as that happens you should be well into the power band and well above any reasonable stall speed anyway. So stall speed doesn't matter then, either.

Where stall speed matters on our working highway truck is in getting that load moving. Then you want torque multiplication right up until the engine enters that part of its power band where it can handle the task at hand without the help. If you delay coupling mode beyond that point all you're doing is burning fuel to make unnecessary and destructive heat. And that's more often than not what happens when a guy tries to use a higher stall converter to keep his trailering rig moving. That clown watches his temperature gauge more than the traffic around him, and needs his *** kicked because of it. What he should have done was solved the problem with higher gear ratio behind and/or more horsepower in front rather than higher stall in the middle.

So, the ultimate reality solution for a highway rig is the lowest stall you can get away with, because with a lower stall rating you have tighter coupling and so get into coupling mode earlier -- and as long as that's all happening, the best time to lock the converter clutch is at the point at which the RPM drop wouldn't otherwise drop the converter back into torque multiplication mode. Yeah, it's like a chain of rubber bands...

 

See, that's why I asked YOU... I wanted a better grasp on the three types of stall, and you gave just that.. and then some!!

It's amazing how misunderstood the tc is, and how its limited builds over the years... And just when I think I got a good grip on it, I learn something more that kabashes that..

Flash stall.. that was my interest.. the difference between flash stall and torque multiplication of a significantly faster moving impeller is where I lost traction, so to speak.. if I have a grip on what you're saying, flash stall isn't the same as true stall, (where the engine starts relying on its own power) bit instead where it has something like an RPM increasing 'free spin' until it reacts.. no?

 

Oh, and the third stall: holds it, but doesn't move it.. like on a hill stationary, giving enough throttle that it doesn't roll backwards..