How to Check the Brakes and Do a Brake Test During Pre-Trip

There is a lot involved in a complete and thorough pre-trip as anyone who has driven for a while can tell you. It is a lot more than just checking a 'few' things. If you are going to do a pre-trip correctly, every single thing has to be checked. It is almost like a major…

There is a lot involved in a complete and thorough pre-trip as anyone who has driven for a while can tell you. It is a lot more than just checking a 'few' things. If you are going to do a pre-trip correctly, every single thing has to be checked. It is almost like a major DOT inspection done by the toughest inspector anyone has ever seen. One guy I knew, who was retired DOT, said the toughest DOT inspectors were in California, Tennessee and Ohio. From my experience, he certainly knew what he was talking about.

In the last article on pre-trips, I ended with the front suspension, spring hangers, springs, U-bolts and saddle and the shocks. Today we are going to start with the entire braking system. This is probably one of the most overlooked and vital areas of all. If the brakes are not right, a lot of people could be in serious trouble including you.

Check the air lines to each brake chamber on the tractor and the trailer. Make sure they are not cracked, bent, broken or leaking. The brake chamber and clamp needs to be secure, and not cracked, bent or broken and the bolts tight. The push rod slack adjuster is secured with pin and cotter pin and no more than 1 inch of play. The S-cam shaft to s-cam roller is the usual – not cracked, bent or broken. The brake shoes must have a minimum of inch inch wear left on the pads and be free of oil, grease and debris. The brake drum must be round, with no excessive wear, man-made welds and free of oil grease and debris.

The air lines from the tractor to the trailer must be lined up and pushed down as far as they will go. The rubber seal or 'grommet' must not be discharged out, cracked or missing. These lines can not touch the catwalk as that can cause scrapes which can cut through and result in an air leak. The air lines on the trailer must be a minimum of 18 inches off the ground so when you go over bumps or large pot holes you do not lose your brakes.

The last thing I wanted to discuss right now is the brake test. For the tractor push the red knot in and put the truck in a low gear and tug. To check the parking brake, push the yellow knob in with the red knob out and tug again. You should not move either time.

To check the service brake and check for suspension problems or a possible needed adjustment, drive a few mph and push in the brake keeping your hands off the steering wheel. If the tractor pulls one way or the other you may need some service.

Once this is done, we are now ready for the air brake test.

Make sure the psi is about 120 to 125, turn off the engine, chock the wheels, and release the brakes, (yellow and red knobs in). You will lose approximate 10- 15 psi. After this you should lose no more than 3 psi per minute. Put your foot on the service brake and push in. Once more, after the initial loss of 10-15 psi you should lose no more than 4 psi per minute.

Put the key in the 'on' position so you can see the gauges but do not start the engine. We need to check the warning light and buzzer so begin fanning the brakes. The buzzer and lights should come on at about 60 psi. Continue fanning and the brake knobs should pop out between 20 and 40 psi.

Now start the tractor, put the tach at about 1000 to 1500 and you should see the air building up fairly quickly. It should take no more than 45 seconds to go from 85 to 100 psi. At approximately 120 psi you should hear the release valve spit. You have just completed your air brake test. Congratulations.