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Do trailer brakes automatically lock when the air lines have been disconnected?
Wiki User
∙ 14y ago
Air pressure within the air braking system of a tractor-trailer (or large truck) is what prevents the brakes from being applied. The pressure of the air pushes back a large spring at each wheel. The large spring will apply the brakes when there is no pressure in the system. When the driver steps on the brake pedal, air is released out of the system and the brakes are applied. When the driver's foot comes off the brake pedal, air is quickly pumped back into the system and the brakes are released. Disconnecting the air line has the same effect on the trailer's brakes. Air is released from the system, and the brakes are applied. It is not the brakes themselves that lock. Application of the brakes causes the wheels to lock.
Wiki User
∙ 14y ago
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What is a tractor trailer protection valve?
protection valve maintains air in the tractor brake system in the event of the trailer air lines becoming compromised.for example, if a trailer line is leaking, broken or disconnected
How can you test the tractor protiction vavle?
I am sure there is a technical way to do this, but quick and dirty: Leave the trailer disconnected from the tractor and tie lines down so the couples are open to the air and they won't flail around. Push the button to Charge the trailer (release trailer park (maxi) brakes) the air flow should stop very quickly. Some older trucks will drop to 80 psi before stopping the flow of air. Some really primitive ones 60 psi.
Why wont my brakes grab on my trailer when I apply them they are air brakes?
Most likely answer is that it has something to do with your brake chamber. Bad brake chamber, bad seal.. something to that effect. There may also possibly be blockage in the air line. When trailers are parked in the yard, at customers, etc., there's usually nothing done to cover the glad hands, and stuff can get into the air lines that way.ANSWERThe most logical answer is the trailer brakes are out of adjustment. A VERY common problem with HD air brakes. DOT will fine you and put you out of service if they catch your running with brakes out of adjustment. Call a road service and get them adjusted properly >before< you hit the road again. A driver is totally and 100% responsible for assuring brakes are properly adjusted and working correctly. If your are sure they are adjusted right make sure your air lines are connected right, red on red, blue on blue, make sure you push in both the red and yellow brake valves on the dash. (charging the trailer brake air supply) If you will hook your trailer, roll your gear up, and then tug against the trailer with both dash valves, or the one big yellow valve, pulled >out< (trailer brakes not charged) and the trailer rolls forward with the tractor your trailer brakes are Definitely out of adjustment. When trailer brakes are properly adjusted a trailer will not budge when the spring brakes are set!!! Brake shoe Adjustment does indeed affect the parking spring brakes ability to lock all wheel's when a trailer has no air charge. Dude! I can't believe you actually passed a CDL air brake test! No offense intended here but you seriously do need some refresher training!! Truckers are legally responsible to make sure their equipment operates properly and is safe on public roads at all times. You have GOT to learn air brake basic man!!
What is a Glad Hands on a trailer truck?
They are what's used to connect the trailer to the trailer supply air lines.
Do you need to bleed the rear brakes on a 1987 dodge Dakota?
If you suspect that there is air (or other contaminants) in the system, or if the lines have been disconnected for any reason, then yes, the brake lines need to be bled. If you've only replaced the brake pads/shoes, etc., then there is usually no reason to bleed the lines except as indicated above.
How do i fix spongy brakes on a landrover?
Spongy brakes on any automobile are usually caused by air in brake lines. The lines need to be bled according to the owner's manual.
Why is a liquid used in a car's braking system?
A liquid is used because it cannot be compressed. Remember the scientific qualities of the three states of matter. Solids have a definite shape and volume. Liquids have a definite volume, but not a definite shape. Gases can not only take the shape of a container like liquids, but with compression, a wide variety of different volumes of gas can fit into the same sized container. Now, you want a 1:1 relationship with the medium in the brake lines and for it not to compress. The reason you bleed the brakes is to get the air out so the brakes won't be spongy, since any air in the lines can be compressed. As hard as the brakes are to operate, a significant amount of air would mean that nothing would happen when you press the brakes. The air would absorb the pressure and the fluid past the air would never get the necessary amount of pressure to operate the brakes. Now trucks do use air brakes, but the system is too bulky to be practical in cars, and not as responsive. They employ a number of workarounds and tricks to make the system work. For instance, most brakes in tractor-trailers require air to release, not apply. That way, they can be much more responsive, since they are operated by heavy springs and the air fights the pressure of the springs. So the brakes are not always prompt in releasing. For the brakes to work in the trailer, there is a relay system, where a separate air tank under the trailer is kept charged, and thus the lines from the truck signal when to use the air from that tank. That is because the distance from the auxiliary tank under the trailer is much closer to the trailer air brakes than to the air tank in the truck.
Why are ths brakes spongy on your 1995 Audi a6 quattro?
You have to bleed your brakes, there is air pockets in the lines...
Can spongy brakes be caused by problem with ABS Controller?
Spongy brakes are caused by air in the brake lines.
What size are semi trailer air brake lines?
Varies by manufacturer.
Why are brakes spongy?
Air in the brake lines would be my first guess.
Why are the Front brakes are sliding just replaced back brakes?
You still have air in the back brake lines or they are not adjusted properly which is making the front brakes take the full load
