parking brake on a semi or firetruck

[Brett Hartwig]

Not exactly a ST question but I figured some of you would have some knowledge of larger trucks. I am trying to get my fellow firefighters to start using wheel chocks whenever they are out of the station and on a call. Seems to me they are on the truck for a reason and it's a safety issue...a little more assurance that the truck won't roll away on them and into a car/person. I am getting a little pushback from some of them though...they argue that the truck can't roll away with the parking brake on. Even if air pressure is lost, the default is for the brakes to lock up so wheel chocks are pointless. I understand the basic design of the system, air holds back large springs when the PB is off, pushes them against the drum when the PB is engaged. But, can't the springs fail, get rusty, fall apart, etc? Can't there be some other catastrophic failure in the system that makes the PB fail? Seems to me like anything is possible, why not take 5 seconds and throw the chocks down. Opinions?

 

[Josh mcleod]

Wheel chalks are not needed. When the park brake is applied air is exhausted from the brake pots which contain a very powerful spring that extends and applies constant break pressure. The air brake system is a great reliable and SAFE system. Wheel chalks are to be used for inspecting/adjusting brakes or for added security when parked on a hill.

I've been driving 18 wheelers for 10 years.

 

[Duane Foster]

If the fire truck is running there's always a possibility, however remote, someone could accidentally bump the air brake button/knob and release the brakes.



Air pressure moves the shoes away from the drum. Without air pressure, the truck isn't moving. You'd have to get under the truck and manually adjust the springs to pull the brake shoe away from the drum. The parts you're worried about failing should get checked when the truck is serviced, which should be done on a regular basis. Fire trucks aren't exposed to the weather day in and day out like other vehicles, and don't get many miles put on them, so failure shouldn't be a big concern.

 

[Josh mcleod]

I should also mention, I'm not familure with fire engines so there may be some differences.

 

[Josh mcleod]

It takes a good amount of force to push/pull the plunger button. It would be highly unlikely to accidentally release the brakes.

 

[Duane Foster]

I know, just saying it could happen, but highly unlikely. I drive a large straight truck with air brakes.

 

[RedRanger 7]

USE THE WHEEL CHOCKS!!! In an emergency situation people are in a panic to assist and want to get out of the vehicle quickly! Ive seen transit buses roll down hills on the news because the driver needed to use the washroom and needed to get out quickly. Im sure you tube has plenty of roll aways because a simple thing is forgotten. Us truck drivers have a lot on our minds when stopping for a delivery or to take a break. :driving:

 

[Richard Toms]

I would say use the chocks. I've been driving a delivery truck of beer for 10 years now and can't believe what happened to me just a few weeks ago.



Work box truck I had, seemed to have a bit of trouble stopping at some points. It was due for a PM but lack of trucks we currently had, it wasn't able to be put in. On this one day, I had like 500 cases of wine and I went to my first stop. Parked it on a slightly downward hill, popped the parking brake on, turned the truck off and proceeded out the door. And the truck started to drift. The brakes can fail even when engaged. I turned the truck on and backed it up and it seems to be fine. Our trucks do not have chocks. One would think they should be there, but I guess the County just can't afford them.



After reporting the problems of the truck, with the battery dead every morning and no parking brake, no A/C, needed new tires. They finally fixed all of these problems about a month later.

 

[Mark K 2]

IIRC, wheel chocks are required by NFPA.

 

[Brett Stoner]

Out of the several thousand commercial vehicles I have inspected and crashes I have reconstructed I have yet to see a parking brake spring failure or a crash related to the failure of a parking brake system. I have seen numerous ones out of adjustment, other broken components, and rusted out brake chambers, but no broken springs. It is a redundant safety measure and may or may not be necessary depending on your risk tolerance. Now granted FD is exempt from regulations so I dont see fire trucks but I would think they would be in great shape given such little miles driven and frequent inspections.

 

[Gavin Allan]

Interesting... I have a related question: Our state requires special testing/licensing for driving air brake vehicles. What additional skills are needed to drive air brake equipped vehicles over , say a large straight truck with hydraulic brakes?

 

[Duane Foster]

It really doesn't require different skills. It's more about knowing how air brakes work, and what to check (and how) on a pre-trip inspection or if there's a problem. I did have to take both a written and driving test when I needed to add the air brake endorsement to my CDL, but it's a one time deal as long as you keep the air brake endorsement when you renew your license. Here in Iowa, they used to ask if I wanted to keep the air brake endorsement when I renewed, but they haven't asked the past few renewals. I always kept it, even when I didn't need it, just to avoid the hassle of taking the test again. Besides, you never know when you might need it, and it doesn't cost extra to have it.



The thing I can't figure - if the truck is licensed for under 26,001 pounds, you don't need an air brake endorsement, even if you drive that truck all the time. The truck still has air brakes, whether it's licensed for 16,000 lbs, or 30,000.

 

[Brett Stoner]

You need a CDL if the gross vehicle weight rating (GVWR) of the truck is over 26,000 lbs. If the vehicle is under 26,001 lbs gross vehicle weight rating then you do not need a CDL.



You only need an air brake endorsement if the truck you are driving requires a CDL and has air brakes. So if you are driving a smaller straight truck (under 26,001 gvwr) and it has air brakes you only need a valid driver's license.



Duane,

The reason is because many of the larger and smaller straight trucks are built on the same frame/chassis but the manufacturer labels them as 26,000 lbs exactly to eliminate 49 CFR 383 and 382 regulations for the purchaser.

 

[Duane Foster]

My point is, air brakes are air brakes, regardless of the truck weight. I understand the distinction from the manufacturers side. From a licensing (endorsement) side, not so much. There was probably a lot of lobbying from the manufacturers and lease companies.