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Old 05-13-2016, 11:21 AM   #15
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Use it as a weapon of last resort. Better to burn up and destroy the brake them plow the coach into something or someone. Its not a very stout break and in a down hill emergency you'll probably get one use out of it.

Don't hit the peddle and floor it. Remember there's no antilock on the brake and if by chance you do lock up the rears the back of the coach will probably become the front of the coach, then they will switch, and switch, (wash-rinse-repeat). You get the idea. As other have mentioned you'll need to hold the release while pushing on the peddle. Steady pressure to get the speed down so you can start down shifting the transmission. The driver is going to be a one legged man in an a__ kicking contest but you'll have a camp fire story that will have everyone's attention.

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Old 05-13-2016, 11:44 AM   #16
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I'm sure it is a diffent story with different type vehicles. I did it once in a Beaver which was rolling because some dumb a$$ (who shall remain nameless to protect the guilty) had forgotten to set the parking brake. The coach was rolling about 5 mph and I jumped in and pulled the yellow knob. The coach stopped instantly, with so much force that the nose dove and the retractable steps hit the ground. It was a violent stop, and I hate to think about what the result would have been at a highway speed.

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Old 05-13-2016, 11:51 AM   #17
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I have. In Oct 15, I was taking the off-ramp in McDonough Ga. after sitting on the interstate for an hour with hot brakes. I thought they had cooled enough, but once I hit the ramp and applied the brakes (at about 35 MPH) they went to the floor. I pulled the yellow knob and it slowed enough to drop it down a couple gears. Thankfully the light was green and was able to make the corner and pull over into a gas station until a wrecker arrived. I was able to change my shorts before the wrecker arrived.

Did an op's check on the parking brake later and they still work fine.
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Old 05-13-2016, 12:42 PM   #18
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With air brakes, the parking brake is applying your service brakes, with the equivalent of 60 psi pressure.

Quicker then the pedal, explaining the quick stop at low speed, but with less force then the pedal, explaining the lack of stopping, when the brakes are overheated while at a higher speed.

The spring in the chamber needs to be able to be compressed with the air system. They release at 60 psi.

Pop them on, at 20 mph, and you will just stop quickly.

Drive shaft mounted parking brakes have an advantage of the gear reduction of the rear differential ratio.
That's how a relatively small brake can lock you up. They also use high friction material.
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Old 05-13-2016, 02:34 PM   #19
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Wrong. With air brakes, the parking brake is applied by very strong springs. When you push the yellow button on the dash, air is applied to overcome the force of the springs and release the brakes. A separate air cylinder operates from the brake pedal to apply the brakes (service brakes). The same brake shoes are operated by two separate systems and two separate cylinders.
With air brakes, if you don't have air pressure, the rig ain't going to move.
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Old 05-13-2016, 02:55 PM   #20
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Originally Posted by ChasA View Post
Wrong. With air brakes, the parking brake is applied by very strong springs. When you push the yellow button on the dash, air is applied to overcome the force of the springs and release the brakes. A separate air cylinder operates from the brake pedal to apply the brakes (service brakes). The same brake shoes are operated by two separate systems and two separate cylinders.
With air brakes, if you don't have air pressure, the rig ain't going to move.
Here is an explanation of parking brakes.

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Old 05-13-2016, 03:10 PM   #21
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More on spring brakes.

Spring brakes for emergency braking and parking


All vehicles with air brakes must have a way of stopping if the service brake system fails. Most vehicle manufacturers combine this emergency braking system with a parking-brake system using spring brakes.

Spring brakes are not air applied like service brakes. They apply when air pressure leaves the brake chamber and release when air pressure builds up in the chamber.

Spring brakes use a different type of brake chamber from service brakes. A brake chamber that includes both service brake and spring brake sections is called a spring brake chamber. (See Diagram 4-1.) Spring brake chambers apply the brakes by means of a large coil spring that provides enough force to hold the brakes in the applied position, instead of using air to apply the brakes.

Spring brake chambers are different in appearance from service brake chambers. To accommodate the large coil spring, a section must be added to the service brake chamber that is clearly visible and adds significantly to its size. The spring brake section is “piggy-backed” onto the service brake section and these two sections function as two separate chambers. The portion nearest the pushrod end is the service brake section and it works in the same manner as a separately mounted service brake chamber.

To release the spring brakes, normally about 414 kPa (60 psi) of air pressure must be supplied to the spring brake chamber to compress or “cage” the spring. If system pressure is below 414 kPa (60 psi), the spring brakes start applying because there is no longer enough pressure to keep them released.

Many vehicles can still be driven even with the spring brakes applied because they do not have the braking power of the full service brake application. Before driving the vehicle, it is important to ensure that the air brake system has enough air pressure (normally 414 kPa (60 psi)) to keep the spring brakes from applying. Due to the way most spring brake chambers are currently constructed, it is very difficult to unintentionally release the spring.

The large coil spring used in the spring brake chamber is compressed under very high tension. Tampering, damage or corrosion can cause the spring to release, resulting in sudden violent motion of parts of the air brake chamber. Since this can be hazardous, never attempt to service or repair any air brake chamber.

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Old 05-13-2016, 08:56 PM   #22
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I have applied the parking brake on our Mandalay at about 50 mph. I did this to test its braking force. The coach came to a stop with the equivalent braking force of a heavy stop with the service brakes. The final stop is a bit abrupt because the brake stays fully applied right down to the stop. It doesn't feather off as you would do when braking normally with the pedal.

Overall, it was a non-event and gave me a good idea of what to expect should I ever have to use it in an emergency.
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Old 05-14-2016, 02:05 AM   #23
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Originally Posted by CJ7365 View Post
I have done some practice on my Jeep CJ7 before, not on the highway but out in the desert, using the same procedure you described, holding the handle and manipulating the pedal.

It was challenging but could be done, rear drums are not the best by themselves though
On a small 4x4 with part time transfer case if you put it in 4wd the rear drums now slow all axles... handy if you ever lose a hydraulic brakes off road...
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Old 05-14-2016, 06:48 AM   #24
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Rich-n-Linda stated it correctly, as this is how it is explained in Camp Freightliner. So, if a DP requires you to pull the P-brake go ahead and do it. It will take time to stop 32,000 lbs or larger of a moving force. No need to change shorts.
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Old 05-14-2016, 08:25 AM   #25
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I used the Emergency Brake on our DP to stop when we experienced a brake pedal failure and could not apply the brakes any other way. Fortunately we were only going about 40 mph at the time, but we were in traffic and we hit two cars in front before finally stopping. Only the rear brakes get applied, so the stopping distance is rather longer than usual.

On a DP, the emergency brake button dumps air from the brake system and allows the brake springs to apply pressure to the brake. It works.

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