What can possibly cause an 18-wheeler to fail its brakes ?

SWEET SARAH

WHEN PULLING A LOAD AND DESCENDING A HILL MOST
TRUCKS HAVE TO GEAR DOWN . IF YOU DO NOT DESCEND HILL SLOW ENOUGH YOU BE ON THE BRAKES TOO MUCH WHICH WILL CREATE TOO MUCH HEAT. THEY WILL FIRST SMOKE AND THEN EVENTUALLY CRYSTALLIZE THE BRAKE SHOE AND THEN LAST WILL CATCH FIRE. MOST TRUCK TODAY HAVE A COMPRESSION BRAKE OR JAKE BRAKE ( BOTH SAME THING). IT WORKS OFF THE ENGINES COMPRESSION TO SLOW THE TRUCK WITH VERY LITTLE USE OF AIR BRAKES. VERY IMPORTANT WHEN YOU DESCEND A HILL TO BE IN PROPER GEAR. WITHOUT A COMPRESSION BRAKE A TRUCK WITH LOAD MUST DECENT A LONG GRADE VERY SLOWLY BETWEEN 6 MPH TO 15 MPH DEPENDING ON HOW HEAVY YOU ARE. A JAKE BRAKE WILL ALLOW A LITTLE MORE SPEED THAN THAT. AIR BRAKES ON A TRUCK HAVE AIR CHAMBERS ON EACH WHEEL WHICH HAVE A LARGE SPRING IN IT LOOK ALMOST LIKE CARS COIL SPRING ON SUSPENSION. THAT SPRING IS HELD BACK BY AIR PRESSURE. WHEN THAT AIR PRESSURE DROPS BETWEEN 20 TO 45 PSI THOSE SPRING ARE NO LONGER HELD BY THE AIR PRESSURE THEY BEGIN TO APPLY THE BRAKES. SO EVEN IF YOU LOSS ALL AIR PRESSURE THESE SPRING BRAKES WILL COME ON--- THEY WILL TOTALLY LOCK UP ALL BRAKES. THAT IS THE VERY BASIC OF TRUCK BRAKES.

magiceye81

unless there is a mechanical breakdown of the brake pads, drums, air chamber, linkage or a frozen airline, i can't imagine how the brakes can fail.

as noted before, the brakes automaticly come on if the air pressure drops below a certain level.

the brake power is greatly reduced, if the brakes are too hot (usualy those types of brake pads are designed to withstand temperatures of up to 700 degrees)
so the best advice is to use the engine and engine brakes if on a down grade. the goal is not to use the brakes at all, so if there is a engine failure or something jumps in front of you, whatever, you have the brakes still available

wuzzel223

To begin with, the brakes on a large truck like that are operated by compressed air. Should a failure in the line occur, bad thing. From what I have learned is that the engine produces the compression.

Eskimo Mom

Brake failure in an 18 wheeler is usually caused by brakes that are badly adjusted &/or too much braking for too long of a time. Hot brakes do not grip & slow the vehicle down. They will smoke & can catch the wheel on fire, causing more problems, if not corrected.

If the air compressor or any part of the air system fails, there is a fail safe device on all 18 wheelers. At a certain psi, usually around 75 psi, a warning light &/or buzzer comes on. The driver has to find a shoulder or a safe place to pull off the road & get the vehicle to a stop because the springs that activate the parking brakes kick in around 15-30psi.

Every commercial 18 wheeler on truck & trailer is required by law to have an annual DOT inspection. The mechanic makes sure the vehicle passes the rules & regulations laid out in the FMCSA (Federal Motor Carriers Safety Administration) Handbook. In addition, every driver is also required to perform a pretrip inspection before the start of the workday & is encouraged to do enroute inspections after stopping for breaks, etc.

Ebony Cowboy

low psi

quik1964

the previous 2 answers have it

Byron

Loss of air pressure would actually apply the brakes, not cause them to disengage. Maybe moisture in the brake system freezing would cause brake failure. Or perhaps they won't work well when they overheat.

q s

Do you mean fail an inspection or fail to stop the truck?

Eric F

if there's air in the brake lines, or a leak

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