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Old 07-14-2014, 08:29 AM   #1
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Apply EMERGENCY brake "at speed" ??

I'd like to hear experiences or opinion as to what happens if you apply the Emergency / Park Brake while traveling "at speed" (45, 65 MPH range). Does the brake lock the rear wheels (dangerous !!!). If on cruise control, does CC disengage?
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Old 07-14-2014, 08:32 AM   #2
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I've applied mine for testing purposes at around 15-20 mph. It slowed me down real quick, but didn't lock the wheels.
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Old 07-14-2014, 08:35 AM   #3
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At Camp Freightliner they show a short video clip of Freightliner test folks doing exactly that. It will stop the coach rapidly, but it doesn't lock the rear wheels.
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Old 07-14-2014, 08:40 AM   #4
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Not sure exactly why you are asking, but in an actual emergency situation, seems the application of brakes via the brake pedal would provide the most effective stop.
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Old 07-14-2014, 08:55 AM   #5
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The auto industry has learned that locking wheels does not stop a vehicle sooner. Brakes are designed to convert energy of motion into heat energy. More heat is generated by correctly working brakes than tires skidding or sliding on pavement.

Would the EB lock the wheels?? No.

I don't know what other chassis use for an EB but the F-53 uses a small drum brake assembly around the drive shaft. It is operated by a mechanical lever and a cable. It will provide one additional brake besides the other four. It is a drum brake which don't work very well. The other four brakes are disc/hydraulic and they will provide significantly greater stopping power than the EB brake.

IMHO! The phrase emergency brake or also called a parking brake is a phrase used for a long time. It really should be called a parking brake. I don't really believe it was ever intended to be used except for parking and in the event you lost either your front or rear brakes. In that situation it will slow you down but not very well. The dual master cylinder has been around since the last 50's or early 60's. In the event of a hydraulic leak (past the master cylinder) you only loose two wheels. So the EB/PB still has two wheels working to help.

I have never used an EB in an emergency but rest assured it won't lock up any wheels.

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Old 07-14-2014, 09:19 AM   #6
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I think the OP was referring to an air brake, not a cable brake.
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Old 07-14-2014, 09:36 AM   #7
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On a coach with air brakes, pulling that big yellow knob, will apply the rear brakes, and bring the coach to a (probably not very rapid) stop. If there were a sudden loss of air pressure while driving the motorhome, the rear brakes will be applied automatically, as it takes air pressure above 50 psi, to keep them released.
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Old 07-14-2014, 09:44 AM   #8
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It seems that I have heard that applying the park brake somehow "clamps" the drive shaft in coaches with air brakes
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Old 07-14-2014, 09:55 AM   #9
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Quote:
Originally Posted by MSHappyCampers View Post
It seems that I have heard that applying the park brake somehow "clamps" the drive shaft in coaches with air brakes

Actually, pulling out that big button dumps the air from the big air brake chambers on the drive axle. The ones back there have a second part and when the air pressure drops below a certain point, large, heavy springs engage and cause the drive axle brakes to be applied.



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Old 07-14-2014, 10:03 AM   #10
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At a driving school the question was asked what to do if the driver becomes incapacitated. Answer was for the copilot to grab the wheel and pull the park brake. Don't try and use the foot brake while standing up, perhaps supporting the driver, and steering the MH.
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Old 07-14-2014, 10:06 AM   #11
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Quote:
Originally Posted by MSHappyCampers View Post
It seems that I have heard that applying the park brake somehow "clamps" the drive shaft in coaches with air brakes
Joe,

CaptBill is right. The air brake chambers on the rear axle are spring loaded, not just a "pancake" type chamber requiring air to apply the service brakes, but an additional chamber that contains a very heavy spring. When you release the air brakes you charge that extra cylinder to pull the actuator rod back from the service brake pancake. When you set the PB/EB the spring in the chamber reapplies that rod to the pancake thereby actuating the brake rod. They are installed on the rear axle as this will stop the vehicle in the safest manner. This is the reason when towing a vehicle with the rear axle on the ground the brake chambers need to be "caged" (manually released with a special T bolt) to release the spring from the service brake pancake.

Some, not all, vehicles that use hydraulic brakes may have a drum or band type brake at the rear of the transmission that will have the same effect. Others use a cable arrangement to actuate the brake shoes on the rear axle.
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Old 07-14-2014, 02:25 PM   #12
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Alot depends on the vehicle,,

Gas motor homes with drive shaft braking: SLOWS the vehicle, will not lock 'em up not powerful enough to do that.

Diesels with air brakes, blown air tank.. See above, Brakes are powerful enough but springs that set them,,, not so much.

Cars.. On a car and most pickups the emergency brake is the same as the service brakes, only operated mechanically instead of hydraulically, so they ARE powerful enough to lock the rear wheels and initiate panavision In fact this is used in Genuine Chauffer's training schools (NOT the one that teaches truck driving but the one that teaches how to protect a VIP when terrorists try to kidnapp him from the LIMO you are driving)

Fact is.. A really good VIP chauffer... The kidnappers might just end up .. "Retired" as it were, from the kidnapping business (And the breathing business) when the smoke clears.

(The smoke, made by the spinning tires on the limo, having obstructed the attacker's view of the sign and the guard rail, causing them to miss the curve and .. Well, it was a high cliff and when they got to the bottom .. they were "Retired".)
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Old 07-14-2014, 02:46 PM   #13
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Your coach does not have an 'emergency brake' It has a parking brake whose sole design purpose is to keep and parked coach stationary without driver involvement.
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Old 07-14-2014, 03:11 PM   #14
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Quote:
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At a driving school the question was asked what to do if the driver becomes incapacitated. Answer was for the copilot to grab the wheel and pull the park brake. Don't try and use the foot brake while standing up, perhaps supporting the driver, and steering the MH.
I have told a few of my More responsible students on my School Bus that very thing with the caution they get(sit) on the floor first.

Quote:
Originally Posted by wa8yxm View Post
Alot depends on the vehicle,,
Gas motor homes with drive shaft braking: SLOWS the vehicle, will not lock 'em up not powerful enough to do that.
Diesels with air brakes, blown air tank.. See above, Brakes are powerful enough but springs that set them,,, not so much.
......
I don't buy for a second the emergency (parking brake) on a air brakes vehicle won't lock the rear wheels.
Whether or not he wheel lock depend on several factors.
First the ABS is not hooked to the parking brake function.
The weight on that axle, brake adjustment, road condition,(Dry,Wet,snow covered,Ice) tire tread.
I Am positive they would lock on mine. 8K-9K lbs on a 20K lbs axle, brakes have 4000 miles on them, and they are adjusted up the way they should be.
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