Engine braking bad for automatic transmission?

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I grew up in east TN where some parts were pretty hilly. There were certainly places in older vehicles where engine braking was not an option. When I tow now in the 2.7 ecoboost, i still use engine braking, but with that tiny displacement engine up there, it just spins and spins with minimal authority, and it’s nearly laughable with a trailer hooked up back there. with “tow mode” engaged, it will automatically engine brake quite aggressively, but it’s still not very potent. It’s like asking a 4cyl Honda to engine brake a 9000 lb (combined) mass.

m
 
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About this topic, my dad always said brakes are cheaper to replace than transmissions. I know other said it here too.
I agree with the moderation and conditional use statement. If it's a very long/steep downhill grade and you have a load/trailer, it's a good idea to downshift manually if your vehicle is not equipped with an assist system. Even if without a load, I will downshift if the grade is long or severe. Brake usage is specific, with cooling periods between applications. Most modern vehicles have DFCO which further helps engine braking (gas engines). I'm not sure about diesel, but I know they don't all have exhaust brakes. I don't agree with the "extra shear" statement in the OP. Transmission fluids are highly engineered and highly refined, and I can't see how downshifting / long coasts could break it down more than the occasional spirited romp, which most of us do from time to time.
 
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Ride the brakes down a very long, mountainous grade and have them "fade" and see if they change their mind about using engine braking instead of their brakes.

I think the quoted part may be correct in theory but is probably a stretch in the real world...
Timely, interesting NTSB report about a crash that killed 18 people that MIGHT have been prevented with engine braking:

 
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I don't remember specifics, just that it was in upstate NY (??) and involved a wedding party/limo and a LOT of people died. I was thinking it ended up in a river but that report says "ravine", but yeah, I'm positive it's the same incident.
 
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I don't remember specifics, just that it was in upstate NY (??) and involved a wedding party/limo and a LOT of people died. I was thinking it ended up in a river but that report says "ravine", but yeah, I'm positive it's the same incident.
The NTSB calculated that the limo was going over 100MPH when it reached the bottom of the hill. Responding police officers noted a strong aroma of burned brakes.
 
I’ve towed for years using a 6L90 behind a 6.0, often going down grades of 8% in the Rocky Mountains with a 7,000 lb trailer. I would manually select 4 th gear. Fifth and sixth were both overdrive gears. Using just the brakes is not an option worth considering. The transmission now has 210,000 miles, but is equipped wth a stand alone radiator style cooler.

For my other vehicles, I take them out of overdrive for the 8 % hill going down into the town of Radium. I still have to brake at certain curves. I often see cars ahead of me with the brake lights on for most of the hill.
 
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One item not mentioned is that with more aggressive downshifts, your transmission pump speed is increased and you'll get more cooler flow which is a good thing.
 
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Most modern automatic boxes lock up pretty much as soon as you get moving. Certainly the AW71-SC's that were in my Volvo's would lock up as soon as it shifted into 2nd. My ZF 8HP, I don't quite understand yet, with the BMW being a mild hybrid it does all sorts of weird and wonderful things I don't quite understand as well as I'd like.
This doesn't apply for engine braking. You hit a bit the brakes, or completely lift the foot from gas and they will unlock.
 
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One item not mentioned is that with more aggressive downshifts, your transmission pump speed is increased and you'll get more cooler flow which is a good thing.
That's true. Anyway some cars have better coolers (towing package) so they are better at engine braking.
A small car, designed for eco city driving, is probably not suitable for long drives over mountains - either the brakes or the transmission will overheat.
 

92saturnsl2

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That's true. Anyway some cars have better coolers (towing package) so they are better at engine braking.
A small car, designed for eco city driving, is probably not suitable for long drives over mountains - either the brakes or the transmission will overheat.
How does a better cooler improve engine braking?
 
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This doesn't apply for engine braking. You hit a bit the brakes, or completely lift the foot from gas and they will unlock.


I don’t think the Mazda SkyActiv transmissions do that. They lock up as soon as you move and the computer provides downshifting as you slow plus engine braking as they determine you are going downhill at a prescribed rate. The TC unlocks very close to stopping.

The key is the computer which dictates everything in the power train.
 

92saturnsl2

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I don’t think the Mazda SkyActiv transmissions do that. They lock up as soon as you move and the computer provides downshifting as you slow plus engine braking as they determine you are going downhill at a prescribed rate. The TC unlocks very close to stopping.

The key is the computer which dictates everything in the power train.
I’m pretty sure that method of torque converter lockup disengagement is a relic of the past now. I’m taking about the brake and throttle mentioned by the previous poster. It was a rudimentary implementation from an era where engine/powertrain controls were not as advanced.

The four speed hydramatics would always drive me nuts when trying to maintain a semi steady cruising speed when following traffic. Because you had to feather the gas pedal to keep distance from the car in front of you, the lockup clutch would constantly engage and disengage the whole time. I haven’t driven any late model vehicles that behave that way, torque converter lockup is controlled using many different parameters now, and they tend to be much more aggressive in maintaining lockup than they used to for fuel economy.
 
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How does a better cooler improve engine braking?
"Engine braking" on an automatic transmission heats up the oil in the unlocked torque converters. The unlocking is dictated by the ECU and in my experience happens almost immediately after touching the brake pedal or when foot is raised from gas pedal.

One can see that that RPMs are dropping a bit (limited by the drag inside TC oil) when foot is raised. If the engine was rigidly connected trough a locked TC, then the RPMs would stay the same, since the vehicle speed would not change that fast.
 
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