Check That Bus!

by James Kraemer
Aschool trip or activity bus with a driver that didn't bother with a pretrip inspection is a driver with a bus you don't want your kids riding.

Here's some basic information to help the school's main chaperon verify that the bus was pretriped and is fit for the road. It takes about ten minutes to do these safety checks. You may want to consider asking the school to include on the field/activity trip form an area for the chaperon and driver to sign-off after checking the bus. Driver's made aware that the school is going to double check these areas before allowing the bus to depart encourages drivers to pretrip their buses.

Keep in mind the information presented here is general and is not a full pretrip of the bus, but a few major areas considered critical to a safe bus. An engine low on motor oil is a bad financial strategy, but brakes out of adjustment is a life-threatening disaster waiting to happen.

Left Front Air Brake Front Brakes (2 minutes): Figure 1-1 shows the most common air brake system used on school buses, s-cam type. One piece conventional style hoods make checking these brakes very easy. Raise and secure the hood. (On a transit style bus (flat nose) have the driver turn the front steering wheel to the far right for access to the right side brake system and to the far left for the left side.)

Look on the back-side of the wheel for a round cylinder with a push rod coming out the brake chamber and connecting to a lever. When you pull on the lever (or slack adjuster) the rod should not move outward more than 3/4 to 1 inch. If it moves beyond 1 inch the brakes are usually considered out-of-adjustment and should be adjusted prior to leaving the school.

Some might argue they're fine for a short trip on level roads, but beware if traveling down long, steep grades. Warm brake drums expand and hot drums expand a lot. Brakes out of adjustment can fail when this happens.

Also, check that the chamber is mounted firmly and the connecting air hoses are not frayed or damaged in any way.

Tires: While checking the brakes also check the tires for damage and excessive wear. Running on a bald or damaged tire or one with very little tread might be a cost cutting measure you can't afford. Check each tire carefully and send the bus back even if only one of the rear duals is found damaged or worn out. Again, here's an indicator the bus is poorly maintained.

Rear Air Brake Rear Brakes (2 minutes): Figure 1-2 shows the most common rear air brake system. These are harder to check. If the rear brakes are hard for you to check, the same may have discouraged the bus driver from checking these as well. The decision to ignore the rear brake check is a bad one, since 75% of the stopping power is managed by the rear brakes. Check em'.

Here's the simplest check I can find, thus far. Securely block at least one wheel. Look under the bus from one side at the rear brake chamber on the other side. The angle between the lever/adjuster arm and air chamber face should be slightly more than 90 degrees when the brakes are applied.

Another way is to watch how far the lever moves while the driver applies and releases the brakes. More than an inch (or so) of movement may indicate the brakes are out of adjustment.

Lights: While outside the bus, check the brake, tail, turn, hazards and headlights. If you find any of these lights are not working properly, you have an indicator the bus was not properly pretriped.

Inside Brake Check (5 minutes): Block at least one wheel. There are usually two air pressure gauges or one gauge with two air pressure indicators. Again, systems vary. For the most common types:

  • The driver should build the air pressure to the cutout point, around 120 pounds, then turn the engine off and release the parking brake.
  • After the air pressure stabilizes, the pressure should not drop more than 2 pounds per minute and no air leaks should be heard.
  • The driver will now fully apply the foot brake. After the air pressure stabilizes, the pressure should not drop more than 3 pounds per minute and no air leaks should be heard.
  • With the key on and engine off the driver can now pump the brakes. The low air warning light and buzzer should come on at about 60 pounds.
  • The driver continuing to pump the brakes should cause the parking brake to engage at some point around 20 pounds or less.

    You may want to check the time it takes for the system to recover. At normal operating RPM (1800 - 2000), it should take about 45 seconds for pressure to build from 85 to 100 psi.

    Keep in mind if any of these items are found out-of-adjustment or defective, you've just been made aware that this bus may be poorly maintained, requiring a closer inspection before allowing it to depart with children on board.

    Arguments from the bus driver, bus mechanics or the transportation department, concerning the information presented here, can be cross-checked with your state's regulatory agency or the bus manufacturer.

    If you have any doubt, check it out. (jk)

    More info on the Net:

    Click Here for Thomas Built

    Here for Freightliner

    Here for Bendix

    The ABCs of Air Brakes for School Bus Drivers - Earning an air-brake endorsement doesn’t mean that a school bus driver fully understands the air-brake system. Here’s a primer that will help to fill in the gaps.


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