I have a question about torque converters and automatic transmissions. If I am stopped on a slight incline, I can hold the car in position without using the brakes by revving the engine slightly above idle. Is this bad for the torque converter? I am familiar with the way torque converters work and I don’t think it is, but I am curious.
Also, do all automatic transmissions have torque converters?
TIA!
–FCOD
Well, it would add some heat load to the fluid wouldn’t it? But I’ve found that if you only need to use very little throttle, and not for a long period, you’d should be OK. YMMV of course.
I believe that all of the “conventional” automatics have torque converters. My Prius has a CVT and no fluid filled torque converter, but that’s kind of a special case.
Thanks. Until February, I’ve only driven stick-shifts, so I get nervous because my brain equates the torque converter to a clutch and says “AGH YOU’RE RUINING THE CLUTCH!”
–FCOD
The parts you are stressing are the same parts that routinely move the entire weight of the car around, so you aren’t going to do any harm. You are going to be sloshing a lot of fluid around, but aside from some heat generated (as mentioned) you’re not going to be wearing anything down.
There are automatic transmissions that are of the “automated clutch” type. These transmissions shift automatically, but have clutches instead of a torque converter.
There’s more info here:
Stopped with the brake on, the torque converter encounters some resistance to its internal fluid motion. If you were on a slope such that if you took your foot off the brake and the car stayed still, it has the same resistance, only now supplied by gravity rather than braking. The force that’s preventing forward motion (braking or gravity) doesn’t matter to the torque converter, so obvioulsy in this precise situation it’s a wash.
But on a slope where the car would roll backwards, you’ve got to rev the engine. This is equivalent to revving it in gear with the brake firmly applied. The more you rev, the more the fluid is heat-stressed. Consider that the transmission fluid is cooled in a radiator that’s at about 200’ F. That fluid gets HOT, and it does deteriorate. When the fluid breaks down, other transmission components can suffer to some degree. Avoiding overheating the fluid is a sensible thing to do.
Where the line is drawn between essentially harmless resistance (e.g., stopped at idle) and significant stress on the fluid, or how long it has to be revved to what engine speed to cause what degree of harm, I don’t know, and maybe no one knows. But every car manufacturer instructs NOT to hold the car on a hill by revving, transmission overhauls are expensive, and there’s no sound reason not to use the brake instead.
So long as you don’t define premature wear as “harm.”
That stuff wears out moving the car around. Why waste some of its lifespan in a practice that doesn’t have the benefit of transporting you down the road?
This makes perfect sense to me. Thanks!
–FCOD
The car I regularly drive is the Prius so I don’t do it with that car, but in my Expedition I’ll occasionally do it if I only need to add a hundred RPM or so. And as I mentioned not for a long period. It’s true that brakes are cheaper to replace than tranny parts.
There’s not much brake wear on a stopped car.
The owner’s manual of every car I have ever owned has said not to use the throttle to hold the car on a hill. I don’t know why, though; maybe they put that in there just for the hell of it.
Can’t disagree with that. Must be a holdover from a discussion regarding down shifting vs. braking to a stop! :smack:
Out of curiosity, why not just use the brake? It will hold you perfectly still just like the throttle game, only not burn more fuel.
I’ve also wondered about this, though.
IIRC the CVT on the Subaru Justy has an electromagnetic clutch instead of a torque converter: under throttle, an electromagnet magnetizes ferrous powder inside the clutch, essentially making the powder solid and locking the clutch up.
If tranny fluid wears out and nice new stuff is cheap, why do they make it so damn hard to change? No drain plug, stupid, messy and touchy filter installation. Why not use a separate cooler like a bigger tow package does and stay out of the hot radiator all together?
Also, towing a heavy load, going along at 50 MPH, with the throttle wide open on a grade, holding speed, is there torque converter slip? Tach says the engine is spinning faster with no increase in speed so what is slipping and why does that burn up the tranny in a mile or three?
At what RPM will my so called transmission lock up solid when chained to a tree and the wheels do not spin? I have been told that at speed, the tranny does not slip. Personal experience says they do slip. What is the ‘straight dope?’
Exactly right as usual. The only thing I would add is that on some transmissions, manually selecting 1st gear will prevent the car from rolling backwards on all but the steepest grades
Most likely answer is cost. A drain plug costs money. On the other side of it, some of the newer cars have an ATF that does not require changing. Of course it is synthetic and costs an arm and leg if you decide to change it.
Sounds like a trans repair bill about to happen. The torque converter will slip up to a point called the stall speed. While it does generate a bunch of heat, I doubt that it hurts the converter. Note: the heat will kill the fluid very quickly, and the cooked fluid will kill the trans. Running a converter at stall can raise the fluid temp by 100F in under 30 seconds. You do not want to run the converter at stall. What you are describing sounds more like a clutch pack slipping. This is bad, Very bad. Bad on toast. The friction material on a clutch pack is very thin. These packs are designed to be engaged or disengaged. The will not tolerate slip. Slip the clutch packs and pretty soon it isn’t going to be cheap.
There is a minimum road speed before the torque converter will lock up. Chained to a tree it isn’t going to happen. On a car with an on/off locking converter it probably occurs at 45 mph give or take. There are some transmissions that will partially lock up at speeds as low as 30 mph.
Hondas and (some) Fords will force 2nd gear at a stop (or while moving) if you select 2. Every automatic I’ve ever driven will force 1st gear when you select the 1 position. Just because you’re stopped in Drive doesn’t mean that 1st is engaged.
In my early driving years, we had a 1982 Honda Civic and on an incline near my house, it would roll backwards in Drive but if you selected 2 it would hold still.
There can be a difference between being in 1st gear in position D and being in 1st gear in position 1 or L.
When you have manually selected 1 or L the trans (again I am not sure all automatic transmissions do this, but I know some that do) the power flow is not quite the same as when you are sitting at the light in drive. I don’t have a auto trans power flow diagram here at home, but if memory servers there is a one way clutch (sprag clutch) that engages when position 1 or L is selected. This serves to give engine braking as well as it doesn’t allow the car to roll backward on a hill (unless the hill is very steep)
Thanks, that splains a lot for me.
No 'belm buddy