I believe the air brakes work the opposite way, and the pneumatic pressure keeps the brakes disengaged, so that if there is a leak or a failure the brakes will actually lock down. Which is why the brakes on a disconnected trailer are automatically engaged.
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Tarnation!
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Very good! (Or very well, more like!)
I see we are pooling our reservoir of puns. My sides can be heard to creek with laughter.
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Yep. You can (though less effectively) do that with an automatic as well. We practiced that in drivers ed.
I’ve seen a truck use on of those IRL. It was kind of frightening to observe.
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An additional factor not yet mentioned above: brake fade.
Brakes have a temperature limit. If they get too hot, the friction suddenly goes to zero. You learn about this in track driving and racing, but it also happens to big trucks. You have to manage brake usage to stay below the fade temperature. The change is very sudden- you go from normal brakes to STEP ON THE PEDAL AND NOTHING HAPPENS from one corner to the next.
Trucks have systems to minimize brake use partly because of this. The biggest one is the “jake brake” which is a form of extreme compression braking that closes all the valves on the engine. Like downshifting a car, but way way stronger. The downside is it is very loud (you’ve no doubt heard trucks roaring on downhills- that’s the jake brake). They are often banned in populated areas, but a trucker unfamiliar with the area might not be prepared for that, so they weren’t managing their brakes as carefully as they would if they knew they were in a jake brake banned area.
I used to live near a big mountain pass that banned Jakes and this sort of thing happened relatively regularly. There was a ton of signage warning about the situation, but truck drivers are human and don’t always pay attention to it. So they’d enter the grade in the wrong gear, not realize how hot their brakes were, and by then it was all too late and the truck ramp was a welcome sight for them.
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Don’t bother with this unless your brakes have failed though. Brake pads are a whole lot cheaper than clutches, synchros, and torque converters. No sense wearing out all that stuff on hills. One exception is when towing. It’s worthwhile then because the tow vehicle’s brakes are working a lot harder than they are supposed to and fade is a possibility (see above).
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I don’t believe this is as much of an issue as many (including yourself here) make it out to be. Or at least isn’t a blanket case anymore depending on your vehicle.
As an example we had rented a newer Hyundai Tucson (4 cyl with a 6 speed auto) two summers ago on a road trip and passed through Utah and Colorado on I-70. It’s specifically programmed with the cruise control active to keep the speed in check purely with engine braking and even downshift as necessary. The vehicle was also very aggressive at keeping the TCC locked and stayed that way 100% on the downhill stretches with the CC active.
I also imagine this is not unique to Hyundai’s and is likely a thing on other newer vehicles as well.
Your example is more about maintaining a set speed. @VeronicaConnor was more addressing the situation where you have need to come to a stop with no brakes, using only gears and engine braking. Somewhat different scenario.
Yes you can downshift (even in an automatic) to slow down but if you have too much momentum and the slope is too steep, you are just as likely to damage clutch or gearbox if your speed is such that the revs are too high. Best only tried in extremis when you really have no brakes.
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Ya, scary stuff. Not sure what kind of truck my Dad’s friend was driving, people said it was a “Semi” but you leave it at that under the circumstances. A steep mountain road, although secondary, not like the one’s depicted here…those videos you posted, people not respecting the “code” response and not slowing down when passing the wreck site, even with flashing lights and cops. Where I live I think that’d get you a ticket; there’s a specific charge for not slowing under construction or emergency zones. Maybe someone needs to develop a “spike strip” like device that deploys in such circumstances and photo ticket’s the offenders…could be a couple tubes like the old gas station dinger, spaced a few feet apart to get a speed reading, camera on a pole. 'Course you could do that all with a speed gun radar, but having a strip on the road would provide a visible and tactile indicator for the driver to remind them to slow down. Make it safer: money maker!
You’re welcome to wear out your transmission as much as you want. I’ll use my brakes.
If your rationale is that manufacturers created features that abuse the transmission therefore it must be okay, then oh honey we have a lot to talk about with regard to how the car industry works. Companies regularly “engineer for marketing” and engineer to increase parts desk revenue.
For example, back in the early 2000s, BMW introduced the “Free maintenance for five years” plan. At the same time, magically, the fluid change intervals on all the gearboxes went from three in the first five years to “lifetime fill”. 80W90 gear oil didn’t instantly get 10000% better. What they figured out is that free maintenance sells cars, and most people don’t keep their cars long enough for the abuse of the gearboxes to become apparent to them.
The cruise control using the transmission could be done for lots of reasons- easier electronic control, smoother ride, an acknowledgment that people notice brake pad wear but don’t notice transmission wear, etc. However preserving the long term health of the vehicle is almost never on the design board for these features.
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When I see the blue barrels used to slow down vehicles I am reminded of a guy who I went to high school named Chris. He was a nice fellow, bright, athletic, captain of the soccer team our senior year. We were in classes together and in physics class the teacher had included a ‘gimme’ question regarding the blue barrels. We had studied inertia and the teacher had asked in the gimme what could be filled in the barrels to slowly decrease the acceleration of a vehicle. Chris in his kind of dopey way said “bricks.” Chris died in the WTC on 9/11 leaving a wife and two small children.
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Coulda used one of these on Wolf Creek Pass. 'Cept we all know Earl wouldna used it anyway.
Well, Earl grabbed on the shifter
And he stabbed her into fifth gear
And then the chromium plated
Fully illuminated
Genuine accessory shift knob
Come right off in his hand
I says, “You wanna screw that thing back on, Earl?”
He was tryin’ to thread it on there
When the fire fell off a’ his cigar
And dropped on down
Sorta rolled around
And then lit in the cuff of Earl’s pants
And burned a hole in his sock
Yeah, sorta set him right on fire
I looked on outta the window
And I started countin’ phone poles
Goin’ by at the rate of four to the seventh power
Well I put two and two together
And added 12 and carried five
And come up with 22 thousand
Telephone poles an hour
I looked at Earl and his eyes was wide
His lip was curled, and his leg was fried
And his hand was froze to the wheel
Like a tongue to a sled in the middle of a blizzard
I says, Earl, “I’m not the type to complain
But the time has come for me to explain
That if you don’t apply some brake real soon
They’re gonna have to pick us up
With a stick and a spoon”
Well, Earl reared back
And cocked his leg
Stepped down as hard as he could on the brake
And the pedal went clear to the floor
And stayed right there on the floor
And he says it was sorta like steppin’ on a plum
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