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Over The Network

Air Brake System Testing

by Fred Thomas
with contributions by Jerry Ray and Ken Tarkin

A procedure for checking the air system in a motorhome with air brakes.

 

AIR GOVERNOR TEST

Start engine and build air until compressor cuts out. Depress service brake [foot brake] 5 lbs at a time until the air compressor cuts in again. Spec should be at 85 lbs or before. Let air built again until the compressor cuts out. Spec is not to exceed 130 lbs.

 

STATIC BRAKE TEST

Stick shift rigs. Turn engine off with coach in gear. Release parking brake. Keep foot off service brake. Air loss should not exceed 2 psi in one minute.

Automatic Transmission: Stop in level location, or block wheels. Place in neutral. Turn engine off and release the parking brake. Keep foot off of service brake. Air loss should not exceed 2 psi per minute.

 

APPLIED BRAKE TEST

Depress service brake [step on foot brake] and keep it depressed for one minute. After the air pressure has stabilized, the air loss should not exceed 3 psi in one minute.

 

LOW AIR WARNING DEVICE

Turn ignition on [key or master switch] DO NOT START ENGINE. Observe the air pressure gauge. Pump service brake until you can see the warning light come on and/or hear the warning buzzer. Must come on at pressures below 60 psi.

 

EMERGENCY BRAKE SYSTEM TEST

Turn off ignition and then reduce air pressure until emergency [parking] brake handle pops up. Should be below 45 psi. Start engine and try to move coach slowly against the emergency brake with low air pressure. Caution should be used so as not to apply too much pressure against the brake and drive train.

This test insures that the rear brakes really did lock up when stopped.

 

EMERGENCY BRAKE TEST

Allow air pressure to build up until it cuts out. Put coach in gear. Release parking brake. Move the coach and apply the parking brake. Ascertain if the emergency brake works.

 

CHECK SERVICE BRAKES

Set coach in motion slowly and apply service brake firmly to see if the steering wheel pulls to left or right.

 

AIR BUILDUP TEST

Air pressure should buildup from 85 to 100 in 45 secs or less.