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Old 09-27-2016, 06:41 PM   #1
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Air Hydraulic brakes

I have been trying to research exactly how this works? I am looking at a a Motorhome that has Air Hydraulic brakes.

Does the air keep the brakes off like normal air brakes and as I step on the brake peddle I am removing some of that air pressure which in turn applies the brakes?

I am see in other posts think of it like a car with vacuum assist but that doesn't really seem to work for me as the motorhome has the yellow park brake button. How does that hold the brakes if it operates differently then I described?

If the air in fact does keep the brakes off then it seems that if I have a leak in the system by park brake will fail as the air leaks out. Also that seems like a lot of pressure to put on the hydraulics all the time when parked.
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Old 09-27-2016, 06:48 PM   #2
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Quote:
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I am looking at a a Motorhome that has Air Hydraulic brakes.
stemo76
WHAT motorhome has "Air Hydraulic brakes"?
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Old 09-27-2016, 07:18 PM   #3
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stemo76
WHAT motorhome has "Air Hydraulic brakes"?
2000 Harney once made by Safari.

Doing more research I see that normal air brakes take pressure to apply the brake and only the park brake uses mechanical brakes in which air is used to keep off.

So I am guessing that the rear discs are double duty, with an inner drum design like a modern car.
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Old 09-27-2016, 07:39 PM   #4
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Originally Posted by stemo76 View Post
2000 Harney once made by Safari.

Doing more research I see that normal air brakes take pressure to apply the brake and only the park brake uses mechanical brakes in which air is used to keep off.

So I am guessing that the rear discs are double duty, with an inner drum design like a modern car.
Yes that's how it works.

Air over hydraulic brakes have air activated master cylinders. They are basicly an air chamber, bolted to a master cylinder.

Most have a indicator rod and over travel switch to let you know how much MC travel you have. The pedal will feel the same, even with no brake fluid.

Air over hyd. brakes have been used on heavy, constrction equipment for years. Wow, back in the 70s. Seen them on standard drum, wedge drum and disk brake systems.

I believe the spring activated, air, parking brake is a smaller drum, inside the rear rotors.
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Old 09-28-2016, 05:14 AM   #5
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Quote:
Originally Posted by stemo76 View Post
2000 Harney once made by Safari.

Doing more research I see that normal air brakes take pressure to apply the brake and only the park brake uses mechanical brakes in which air is used to keep off.

So I am guessing that the rear discs are double duty, with an inner drum design like a modern car.
stemo76
I believe that Harney coaches built by Safari Motorcoach Corporation, (SMC)... as well as the Safari and Beaver coaches...used the Magnum chassis built by Magnum Manufacturing, (a division of SMC).

My Safari has "hydraulic disc brakes with electric backup".

The "park brake" on my coach is a "hydraulic assisted drum brake" in the drive train, (forward of the Allison transmission).

See: "The Service Brakes", (page 11), and "Air-Over-Hydraulic Brakes", (page 12), of this pdf: http://beaveramb.org/wp-content/uplo...s-Manual-1.pdf

Mel
'96 Safari Sahara, (on a Magnum Blue Streak Chassis)
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Old 09-28-2016, 06:55 AM   #6
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Thanks for the link. I have had a real tough time finding any details on this coach.

This unit has air ride and the air over hydraulic listed in this document.
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