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Old 07-20-2018, 01:27 PM   #15
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I'm far from being a mechanic, but I seem to remember that with air brakes the park brake clamps the drive shaft instead of actually applying the brakes?
Haven't seen that on any diesel pusher, maybe on some gas rigs.
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Old 07-20-2018, 01:28 PM   #16
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Joe, when you release your park brake, air pressure over-rides the spring pressure in the spring brake chamber (rear brakes only) and forces the spring pressure OFF the brake push rod. If you lose all air pressure, or if you pull the park brake knob, air pressure in the spring brake chamber is released; the spring applies the brake.



If this diagram posts, you will see that the rear brakes have dual chambers, one for the spring and one for the service brakes which are applied when you step on the brake pedal (if you have sufficient air pressure).
Your front brakes only have a single chamber for each brake; no spring brakes. Therefore, the parking brake system only applies the rear brakes by spring pressure.
I've never set the brakes while running 60 mph, but I've heard others state that you get a firm brake application, but not a lockup (on dry pavement; if on wet or dirt/gravel, all bets are off).
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Old 07-20-2018, 01:31 PM   #17
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Where is the parking brake located? Could she even reach past you to apply it.

I would think downshifting would slow you down considerably if she couldn't reach the parking brake.

But...

If you think there is a real danger to having a heart attack while driving you might want to reconsider driving a huge lethal object, putting countless number of people at risk.

I've had a heart attack and stroke. I am very familiar with the symptoms. In my case they were not the traditional left arm pains. Same thing with the stroke, not typical symptoms. You really should be aware of what the symptoms are if you think you're a candidate for a heart attack.

If you're driving and there is a hint of something not quite right stop the darn vehicle even if that means on the shoulder of a freeway.

And while we're on the subject, if you think you're having a heart attack don't drive yourself or have your wife drive you to the hospital, call 911. The biggest mistake we made when I had my first heart attack was my wife drove me to the hospital. When we got there I was in full cardiac arrest with 100% blockage. I'm lucky to be alive. An ambulance could have started treatment before cardiac arrest and maybe even prevented it.
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Old 07-20-2018, 01:40 PM   #18
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Rear wheels dont lock up on dry pavement! Dont ask how i know........
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Old 07-20-2018, 01:52 PM   #19
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Where is the parking brake located? Could she even reach past you to apply it.

I would think downshifting would slow you down considerably if she couldn't reach the parking brake.

But...

If you think there is a real danger to having a heart attack while driving you might want to reconsider driving a huge lethal object, putting countless number of people at risk.

I've had a heart attack and stroke. I am very familiar with the symptoms. In my case they were not the traditional left arm pains. Same thing with the stroke, not typical symptoms. You really should be aware of what the symptoms are if you think you're a candidate for a heart attack.

If you're driving and there is a hint of something not quite right stop the darn vehicle even if that means on the shoulder of a freeway.

And while we're on the subject, if you think you're having a heart attack don't drive yourself or have your wife drive you to the hospital, call 911. The biggest mistake we made when I had my first heart attack was my wife drove me to the hospital. When we got there I was in full cardiac arrest with 100% blockage. I'm lucky to be alive. An ambulance could have started treatment before cardiac arrest and maybe even prevented it.

Sure glad you made it! I've never had any heart problems, and don't remember any of my immediate family having any. I just used that as an example for anything that could incapacitate me while driving.
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Old 07-20-2018, 01:55 PM   #20
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Rear wheels dont lock up on dry pavement! Dont ask how i know........



Did you actually have this happen? This is the kind of info I'm looking for!
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Old 07-20-2018, 01:56 PM   #21
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The spring brake application will be rather un-eventfull, even at 60 MPH.

The spring, as shown in the above posts, is released with air pressure. That pressure is about 45 psi. If you were to hold the button in while building air, they would start to reliese at 45 to 50 psi. 60 psi locks in the button.

Remember your air brake safety check, pump the brakes until the parking brake knob pops out. It should pop at 45 psi.

Knowing that 45 psi holds them off, the spring will only apply the force equivalent to a 45 psi brake pedal application.

With 120 psi system pressures, that's just enough for a smooth but firm stop. No skidding or swerving on dry road.

I recall poping the parking brake on our Mack snow plow truck, in an attempt to get it to spin a U turn, in snow, but that didn't work. It was an older truck that had a hand control for the rear brakes, and pulling that got me spinning.

If you have the type of MH that uses an air parking brake, on the drive shaft, ( Alpine and a few others with hydraulic service brakes), that's a whole different thing. Haven't tried that, but Payloaders have drive shaft spring brakes, and they also coast to a abrupt but safe stop.

Last thought.
Do you think the D.O.T. would let the manufactures install a system that locks up the rear tires, in a complete air loss situation ?
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Old 07-20-2018, 02:02 PM   #22
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Did you actually have this happen? This is the kind of info I'm looking for!
If you pull the yellow park brake knob, the brakes will firmly apply. I have done this at least four times. Twice was a manufacturer rep. showing how to use the brake and twice was a sudden loss of air pressure on a customers motorhome. Not a single time did I feel in danger or uneasy.
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Old 07-20-2018, 02:16 PM   #23
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Rear wheels dont lock up on dry pavement! Dont ask how i know........
Well, I'm asking, how do you know?
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Old 07-20-2018, 02:16 PM   #24
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If I remember correctly, the rear spring brakes on apply about 60% of a full, hard brake application and shouldn't throw you into a skid an a straight away. I've not had that happen in a motorhome or bus, but have had it happen in a tractor/trailer due to a broken air line. Had a heavy dozer on a lowboy going about 55. Had to change my shorts, but I stayed pretty much in a straight line.

Lesson I learned about brake application will driving on interior Alaska roads in the winter is that the skidding axle will try to pass the one still rolling. Sound counter intuitive, but it's a fact.
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Old 07-20-2018, 02:28 PM   #25
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Twinboat is right, max application pressure will be aprox. 60 psi.
Just try a 60 psi application while cruising down the road. You will not lock up the wheels, so it will be the same, only the rear axel will be applying, so a slower stop.
Most likely you have ABS, so that's another safety net for you.
As others have said, you most likely will feel a heart attack coming on. STOP! It will not matter where you are, just stop.
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Old 07-20-2018, 02:29 PM   #26
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The spring brake application will be rather un-eventfull, even at 60 MPH.

The spring, as shown in the above posts, is released with air pressure. That pressure is about 45 psi. If you were to hold the button in while building air, they would start to reliese at 45 to 50 psi. 60 psi locks in the button.

Remember your air brake safety check, pump the brakes until the parking brake knob pops out. It should pop at 45 psi.

Knowing that 45 psi holds them off, the spring will only apply the force equivalent to a 45 psi brake pedal application.

With 120 psi system pressures, that's just enough for a smooth but firm stop. No skidding or swerving on dry road.

I recall poping the parking brake on our Mack snow plow truck, in an attempt to get it to spin a U turn, in snow, but that didn't work. It was an older truck that had a hand control for the rear brakes, and pulling that got me spinning.

If you have the type of MH that uses an air parking brake, on the drive shaft, ( Alpine and a few others with hydraulic service brakes), that's a whole different thing. Haven't tried that, but Payloaders have drive shaft spring brakes, and they also coast to a abrupt but safe stop.

Last thought.
Do you think the D.O.T. would let the manufactures install a system that locks up the rear tires, in a complete air loss situation ?

Great info! Thanks!
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Old 07-20-2018, 02:35 PM   #27
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I understand addressing hypothetical situations, but if this is a real concern due to known medical problems, you probably shouldn’t be driving. Let Annette drive. If she doesn’t know how, there are excellent driving instructors available who can teach her in your own rig. We took a course, and it was invaluable for both skills and confidence. Don’t knowing,y out her and others on the road into a dangerous situation.
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Old 07-20-2018, 02:43 PM   #28
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I understand addressing hypothetical situations, but if this is a real concern due to known medical problems, you probably shouldn’t be driving. Let Annette drive. If she doesn’t know how, there are excellent driving instructors available who can teach her in your own rig. We took a course, and it was invaluable for both skills and confidence. Don’t knowing,y out her and others on the road into a dangerous situation.

Look at my post #19. No, I wouldn't knowingly put Annette or anyone else on the road at risk! As much as we love RV'ing, I would not drive with any known condition that could leave me incapable of controlling the rig. I do appreciate your concern!
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