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Old 10-05-2013, 08:16 AM   #1
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Air parking brake on DP

I just wondering about something. Can the parking brake be trusted on all grades? Should I worry and maybe block the wheels to for extra measure? Has anyone ever experienced their coach moving after setting the brake? This is something I would rather learn from others, than experience myself.


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Old 10-05-2013, 08:47 AM   #2
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From what I've read, yes. What the parking brake does for air systems is release the air stored in the lines....that's the noise you hear when you pull the plunger out. When the air is released, the brakes 'slam shut' so to speak.

Again, with any brake advice, it's your safety, it's your life. To be sure, check with your particular coach manufacturer.

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Old 10-05-2013, 09:10 AM   #3
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About the only way the parking brake on a DP, will not hold is if the springs in the brake chambers fail. That is unlikely. However if you are on that much of an incline, blocking the tires is ALWAYS a good idea. While I do not block my tire most of the time I DO block them if I am working around/under the vehicle.
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Old 10-05-2013, 09:22 AM   #4
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If you brakes shoes are good and you brakes are properly adjusted, they will hold. If not, will not hold on steep grades. If you brakes are bad you can drive off with the parking brakes set. Most all newer rigs have automatic slack adjusters so brake stay adjusted all the time, unless your shoes and drums get worn too bad. At that point the service brakes will not be very good either. And keeping the s cams bushings and slack adjusters greesed makes everything work like new. We do this every 10 K on the semi trucks along with oil change and oil and fuel filters. New air filters every 50 K.
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Old 10-05-2013, 09:32 AM   #5
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Air brakes on class a coaches are Spring Applied Air Released and have Automatic Slack Adjusters to keep the brake pads the proper distance from the drums. They are on the rear axel. When you move the air brake parking selector to the park position the air to these brakes is released and the springs automatically apply the brakes. Until your air pressure is sufficient to release the springs the coach will not move.
If you have an air loss while driving the spring applied brakes will activate and park you in the road.
I would suggest that you study up on air brakes.

Some over the road drivers are still required to chock both sides of the drive wheel.
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Old 10-05-2013, 10:37 AM   #6
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The springs in the parking brakes get weak just like any other spring over time... They replace those in our work trucks every few years... If in doubt,,, set the parking brake, put it in gear with engine running, and Gently apply throttle to see how much the brakes are holding... If it moves easily, then it's time to replace them... If in doubt,,, YES chock the wheels !!!
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Old 10-05-2013, 10:57 AM   #7
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Unlike a gas MH , that may have a park pawl in the transmission as well as the parking brake , two systems to prevent vehicle movement .
A DP with air brakes has only , one . The spring brakes, on the rear axle.
Many horror stories, grand kids hit the button while coach was parked, releasing the brakes, even pets .
"Murphy" says , chock the wheels, it's your only secondary system to prevent movement.
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Old 10-05-2013, 11:48 AM   #8
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Thanks everyone, I am well aquatinted with how air brakes work. However, there is just something about a spring loaded brake that didn't sound totally trustworthy to me. I know the big rigs use them, but they are generally locking the drive axles and the trailer axles at the same time. I was just concerned that a 40 ft with a single rear axle might be pushing the parking brake to the limit. Skip, I think I am going to be taking your advise, I want that second brake. I gotta get a set of wheel chalks.. Mr Murphy lives with me... Face palm :::

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Old 10-05-2013, 12:12 PM   #9
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I bought NEW Brake chambers for my RV this last summer for $38 each (only 2 per axle).
These are what contain the springs and apply the service and park (spring) brakes .
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Old 10-05-2013, 12:47 PM   #10
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The parking brake must be inherently weak. The reason I say that is a statement in the owners manual. It says if you drive off with the parking brake activated it will damage/ruin the rear brakes. I carry one of the large aluminum commercial HDT chocks, in case I have to park on a grade where movement might be possible. Takes 5 minutes to place/remove that chock. I'd much rather lose 10 minutes than someone's life.
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Old 10-05-2013, 12:52 PM   #11
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Easiest way to check leave parking brake on and put in gear.

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