Great points. Leaking air is less of a problem then leaking brake fluid. I have always had this strange idea that the best solutions both financially and performance wise are ultimatly adopted. Eventually, I see a common place where both will end up. Electronic brakes with actuators and individual drive motors that also brake at each wheel. Hydraulic motors now have that function on some vehicles but electrical is the way to go. The connectivity is definitely the big reason for air brakes in semis like it is in trains for now.
To clarify one thing, service brake(foot brake) of a road vehicle is applied by air pressure, not the lack thereof. Only the parking brake is applied by dumping air pressure from a separate brake chamber with a hand valve, or the lose of storage tank pressure.
I, too, have a CDL and I think air brake is great except for use in sports car, which should have rock hard, communicative brake pedal. However, air brakes are great only for those who know how to use it. Looking back at my CDL training and certification, thereâs a whole section in the DMVâs written test dedicated to air brake.
Drivers trained to use air brakes need to know compressorâs cut in, cut out pressure, and low pressure warning. Knowing these operation parameters allows the driver to notice a problem early on and pull over before the parking brake applies automatically in the middle of the road.
Drivers also need to be trained to use the brake properly. To bring the vehicle to a stop, the brake pedal needs to be pushed down in one smooth continuous stroke. Multiple applications for a single stop is known as âfanning the brakesâ and it unnecessarily reduces the storage tanksâ pressure.
Typically, drivers have to dump their air tank at the end of each day to release the moisture that has made it pass the air dryer. And build up the air pressure the next day. This is not a problem for professional drivers who have to perform a pretrip inspection. Just walk around the rig with the engine on and the tanks gets filled. But drivers of a regular car would prefer to just turn the key and go
I agree @chunkyazian ⊠a lot of drivers today couldnât get by without the government giving them âbabysittingâ devices on their vehicles like ABS and TPMS. Can you imagine what would happen if most drivers had to do a simple task or two to keep their air brakes working properly? There would be abandoned vehicles everywhere and those drivers would be crying to the government to do something about it.
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I havenât caught up on all the other responses to the original question yet, but here are my thoughts:
The main advantage of air brakes is that they are easy to connect and disconnect from the trailer. When a vehicle with a hydraulic brake system pulls a heavy trailer, the trailer needs its own brake system, usually electric brakes controlled by a separate brake control unit if theyâre not surge brakes. Controlling your brake system with air instead of hydraulic fluid means the trailer and the truck can use the same brake system.
Itâs also been my experience that air brake systems are prone to leaking and compressor issues. It might amaze you to know how many semis out there are leaking air from their brake systems, but the leak is small enough that the compressor can keep up.
@Barkydogâ: âJust cause I do not know, do air brakes lock up when they loose pressure? Are air brakes a little more maintenance due to moisture building up in the system?â
You can usually spot where a semi has lost air pressure and the brakes locked up before the driver could pull off the road. There will be two pairs of tire tracks on the road where the trailer tires dragged as the driver pulled off the road. You can see these markings on interstates all over the U.S. if you look for them.
Okay, now that Iâve skimmed all of the responses, Iâd like to add something some of you might not know. On every semi there are two brake air lines, one red and one blue. I donât remember which one is which, but one of the lines releases the brakes when it gets pressurized. When you have no air pressure, the brakes are applied by springs. The other line actually applies the brakes when you press the brake pedal. Some yard jockies (people whose job it is to move trailers around) will only hook up one line to save time when theyâre moving trailers around the yard.
@wheresrick , itâs been my experience that warped rotors are usually the result of people using cheap white box crap rotors. You get what you pay for. I use Brembos on my Mustang w/EBC (red) pads, and have never had a rotor warp, even after two track days at VIR. On my F-150 has EBC rotors and pads, and doesnât have any issues with warping rotors. Back when I was 18, I had a 1992 T-Bird SC, and being broke half the time I decided to go with the cheapest rotors Western Auto had on hand. Needless to say the quality of these rotors was lacking, and the front two rotors warped within two months of installation. I ended up replacing them both with higher quality rotors, and had no further problems.
A minor correction, hydraulic brakes operate at a higher pressure than air brakes. Air brakes are in the 100-120 psi range and hydraulic brakes are in the 1500-2000 psi range. This makes all the parts much smaller for cars and small trucks. The reaction time, as some have suggested, is much faster with hydraulic brakes because there is very little compressibility where in an air brake there is a lot of compressibility - all indirect because of the mechanism. The delay and the packaging size (plus the cost of a compressor) is likely what keeps smaller vehicles from using air brakes.
Iâve driven a big-rig with air brakes, they stop really well for an 80,000 lb vehicle. The pedal feel is not acceptable for most drivers, or thatâs what brake engineers tell me. I have no issues with the feel, its just different, thatâs all. As side note, if you like shifting gears, youâll have a ball, for awhile.
As for disk brakes versus drum brakes; Drum brakes fade because as the drum gets hot it expands and the shoe no longer has full contact. When is the last time you saw drum brakes at the Indy 500? Or on a NASCAR racecar? Probably the 60âs for Indy and the 70âs for NASCAR.
It amazes me when I watch a show like"Ice Road Truckers" that they do not have an efficient electric brake system(it sure would cut down on thier ice buildup problems in the brake system,its a pain around here even when the air drier isnt functioning properly.On the modern airbrake systems the spring part on the rear brakes engages the brakes when air pressure is lost,if your brakes air adjusted properly it will lock the wheels,some old systems didnt have this feature,when the air pressure went-the parking brakes went too-Kevin
Air brakes are heavier than the hydraulic system. Auto manufacturers are pulling every trick they can think of to lower weight to increase gas mileage. I doubt they would put air brakes on.
Nobodyâs mentioned the air compressor yet.
I think a great many drivers would object to the noise level when it kicks in. Not to mention the purge valve
With engine bays being jampacked nowadays, where would you even place it. Even if smaller, âautomotiveâ air compressors were designed, where do they go? Perhaps some genius would design an air compressor that isnât belt driven.
My brotherâs Mazda has an electro-hydraulic power steering system. The pump is hidden inside the fender well.
Somebody mentioned air starters . . .
On the road air brake vehicles donât have air starters
My folks did not like the noise of the auto leveling feature in whatever gm van they had,
Air starters are known to be very reliable and long lasting,most people cant stand the racket,dont know if its true now but the yard tractors used to use a lot of air starters and an air pump and a storage tank you are ready to go(remember on âMad Maxâ when the auto gyro pilot had to pump the starting system up on the âMackâ tractor that Max got going?) but air is messy and noisy-but very reliable.almost like steam and some vehicles do indeed have small compressors for different reasons(tire inflation systems ,suspension,etc) but its a needless complication-Kevin
as for some yard jockeys only hooking up one air line. that is true. in my experience the yard jockey that does this is the same one who does not take time to make sure the 5th wheel locks in properly, and drops trailers, wasting time and damaging the equip. and the lot. they are constantly stopping to build up air pressure, wasting time. they often rip off air lines when unhooking or when they drop trailer off 5th wheel. they also don t bother to put even one chain on loads in the yard, and crush the secretaries car when they lose pieces off a load. and they drag trailers with the brakes locked around the lot, causing more damage. two air lines are there for a reason. they should be used properly
On the road air brake vehicles don't have air starters
The fuel tankers that deliver to my local gas staton do. I get to hear them every day.
Auto air pumps have been around for over 40 years. They have a small electric motor turning a pump. It is used to inflate air shocks or air springs as needed. Sensors measure the ride height and turn the compressor on to raise the car or truck or use a purge valve to release air to get the correct bumper height. Custom air ride systems are available aftermarket to create very low riding cars for a custom look that can be raised to allow the owner to enter a driveway or drive over a speed bump. You canât âbounceâ one like some âlowridersâ they use hydraulics.
A compressor noise reduction project at a GM supplier did such a fine job, Buick owners complained that they couldnât tell if the compressor was working or not. They put in a dash board light that indicated when the compressor was running - some folks just arenât satisfied!
As for disk brakes versus drum brakes; Drum brakes fade because as the drum gets hot it expands and the shoe no longer has full contact. When is the last time you saw drum brakes at the Indy 500? Or on a NASCAR racecar? Probably the 60's for Indy and the 70's for NASCAR.
I must disagree. Drum brakes also went away after getting wet from fording a stream and you had almost no brakes until they dried. Drum expansion had nothing to do with this.
Itâs the self actuation built into drum brake designs that was the problem. As the coefficient of friction reduced from getting wet or from overheating, the self actuation also went away compounding the effect. Less friction plus less pressure on the brake drum due to lower self actuation and itâs like the brakes completely went away.
Disk brakes fade too, but the reduction in braking is only proportional to the loss of friction and not compounded by the loss of self actuation.
Some race cars in the drum brake era had double trailing shoes instead of a leading and a trailing shoe. There is no self actuation in such a design and thus it needed a lot of pedal pressure or power assist to be usable, however, it worked the same hot or cold and the braking force was very linear and predictable.
Years ago, a friend had a problem with the car that he just put brand new brake shoes in, one front wheel would lock up and the other didnât seem to brake at all. We pulled the drums off and it turned out he put both leading shoes on one wheel and both trailing shoes on the other wheel.
On trucks equipped with air brakes, do the front wheels the wheels that steer the truck, do they have air brakes? Do they have ANY brakes?
Yes, the steering wheels are connected to the air brake system.
Dont know if it happens now,but used to be you could delete the front brakes on heavy trucks for control reasons(most of the time the âpony axlesâ even have brakes now)-Kevin