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Old 11-15-2012, 01:04 PM   #43
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As far as air brakes versus hydraulic brakes, air brake systems are far superior in braking heavy loads.
That's absolutely false. Brakes work on a simple equation of force and friction versus mass and momentum. It matters not whether the force acting on brake shoes or pads is hydraulic or pneumatic.

In fact in heavy duty applications like mine pit haul trucks the trend is away from air brakes in favour of hydraulic brakes because they're faster and more secure.

From an article in Construction Equipment Guide;

"Full-power hydraulic brake systems with ABS result in shorter stopping distances, which also contributes to safer truck operation. Based upon physical design alone, hydraulic systems with ABS will stop in shorter distances than comparable air brake systems. The compressibility of air contributes to delays in braking performance. Hydraulics, however, are virtually incompressible, resulting in reduced delays in brake application.

What does this mean to a driver? Picture a million-dollar haul truck heading down a steep grade in an open pit mine. At just 30 mph (48 kmh), the truck is covering 44 ft. (13 m) in a second. If a hydraulic system causes the truck to come to a stop just one quarter of a second sooner than a comparable air brake system, that’s a difference of 11 ft. (3.3 m). That quarter of a second and corresponding 11 ft. can make a major difference — the difference in work going on or an investigation beginning, the difference in equipment repair costs or business as usual, the difference in life or death."

Hydraulic brakes are not (yet) used in things like transport trucks because the fluid that spilled out when you split the system to disconnect from the trailer would offend our friends at the EPA. So far they haven't outlawed the release of air into the environment though.

Brake fade will happen in any system and with drum brakes like on a heavy truck system, the brakes will be nearly useless from heat long before the fluid in the cylinders gets to the boiling point anyways.
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Old 11-15-2012, 01:07 PM   #44
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Quote:
Originally Posted by slickest1 View Post
As far as air brakes versus hydraulic brakes, air brake systems are far superior in braking heavy loads. If hydraulic was better they would be in use. Light duty trucks use hydraulic and heavy duty use air. Light duty motorhomes use hydraulic and heavy duty use air. When you get a heavy vehicle braking on a long hill the brake fluid in a hydraulic system will heat up and boil in some cases rendering brakes useless.
... .
I still maintain that mhs have air brakes because that's what they use for semi trucks (for trailer connections) and it's a lot simpler and cheaper to re-use same / similar components and it has nothing to do with what's better. Disk brakes are better than drums especially in high heat. Carbon and composite brakes are better steel (I believe I've heard that with carbon brakes on F1 cars, braking distances are about 1/3 what they would be if they used steel brakes and there's very little fade) but trucks use steel drum brakes because they are MUCH cheaper.

Boeing 747s use hydraulic brakes (carbon) - I strongly suspect that if air brakes were better, they'd use air brakes (planes are completely custom application so they can use whatever functions best for the application and cost isn't really an issue). Fully loaded, 747s are up to almost 1,000,000 lbs and they land going close to 200 mph - if it can stop that, I'm sure it can stop a truck.

I'm not saying that hydraulic is necessarily better than air but I don't buy that air is better because that's what they use and if hydraulic was better, they'd use that.

I've never driven one but Wertern RV Alpine DPs had hydraulic brakes instead of air brakes and the reviews I've read said that the brakes were fantastic (almost like driving a car). This link http://www.rvadvice.com/rvarticles/1chassis.html says
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Upstart Alpine (Western Recreational Vehicles) designed their chassis with braking and handling as the main characteristics and have earned recognition for the superior handling brought on by the Toyo tires and i.P.d suspension products. They also were tested and rated on top of the industry by Bendix brakes (using a hydraulic braking system instead of the normal air brakes for a chassis this size).
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Old 11-15-2012, 04:44 PM   #45
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Hydraulic oil will heat and affect braking and you wont know until your brake pedal gets spungee or sinks to the floor. Air leaks are not as big a deal as air is stored in two tanks and you have a guage to monitor your pressure. If you lose to much air the spring brakes will engage. Much safer system.
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Old 11-15-2012, 09:51 PM   #46
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If I'm from a state that does not require an air-brake endorsement traveling into an endorsement area, am I OK?
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Old 11-15-2012, 10:42 PM   #47
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If you are properly licensed in your state you are properly licensed in the other states. They all have a reciprocal agreement.

Happy trails.
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Old 11-15-2012, 11:00 PM   #48
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Having worked on both hyd systems and air, I like air!!!!! Most brake fad is caused by the brake fluid boiling ergo compressability. With a 30 chamber and 120 psi you get 32000 lbs of force on the s cams. Most light truck and auto brake systems have a max of about 1200 psi brake fluid pressure. With a 3" caliper piston you get 11340 lps of force on the disk pads. I like the 32000 lbs force. With hydraulic brakes DOT says 0 leaks, none, nada. With air brakes you get 30 psi with full pedal app over 90 seconds. The glad hand connectors used in big rigs leak some always and DOT says you cannot tap into a hydraulic system for trailor brakes (electric comes to mind)
Hope this helps O ya my discovery has 8x15 front brakes and 10x15 rears. A one ton dually with rear drums has 2x12 or 3x12s
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Old 11-16-2012, 01:54 AM   #49
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Having worked on both hyd systems and air, I like air!!!!! Most brake fad is caused by the brake fluid boiling ergo compressability. With a 30 chamber and 120 psi you get 32000 lbs of force on the s cams. Most light truck and auto brake systems have a max of about 1200 psi brake fluid pressure. With a 3" caliper piston you get 11340 lps of force on the disk pads. I like the 32000 lbs force. With hydraulic brakes DOT says 0 leaks, none, nada. With air brakes you get 30 psi with full pedal app over 90 seconds. The glad hand connectors used in big rigs leak some always and DOT says you cannot tap into a hydraulic system for trailor brakes (electric comes to mind)
Hope this helps O ya my discovery has 8x15 front brakes and 10x15 rears. A one ton dually with rear drums has 2x12 or 3x12s
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Old 11-16-2012, 09:50 AM   #50
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Having worked on both hyd systems and air, I like air!!!!! Most brake fad is caused by the brake fluid boiling ergo compressability.

With a 30 chamber and 120 psi you get 32000 lbs of force on the s cams. Most light truck and auto brake systems have a max of about 1200 psi brake fluid pressure. With a 3" caliper piston you get 11340 lps of force on the disk pads. I like the 32000 lbs force.


Hope this helps O ya my discovery has 8x15 front brakes and 10x15 rears. A one ton dually with rear drums has 2x12 or 3x12s
Holy cow!!! Do you think you could find two more unrelated chassis' to compare?

A 26,500 pound GVWR Frieghtliner chassis and an 11,000 pound GVWR pickup truck?

Gosh, a difference of 250% in GVWR and we're supposed to be surprised at a difference of that much in braking? Seriously?

BTW, if "Most brake fad is caused by the brake fluid boiling ergo compressability" then air brakes should have very little brake fade at all right?

That explains all those "runaway truck" lanes I see all over the mountains. Not!
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Old 11-16-2012, 01:39 PM   #51
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Holy cow!!! Do you think you could find two more unrelated chassis' to compare?

A 26,500 pound GVWR Frieghtliner chassis and an 11,000 pound GVWR pickup truck?

Gosh, a difference of 250% in GVWR and we're supposed to be surprised at a difference of that much in braking? Seriously?

BTW, if "Most brake fad is caused by the brake fluid boiling ergo compressability" then air brakes should have very little brake fade at all right?

That explains all those "runaway truck" lanes I see all over the mountains. Not!

Not such a stretch as comparing Motor homes to Air liners and heavy haul mine trucks.

The original poster asked if he should get an air brake endorsement. He has got some good advice and a bunch of crap. I hope it does not put him off asking another simple question.
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Old 11-16-2012, 01:43 PM   #52
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Totally agree with the endorsement. Does give you a good understanding of the operation of the brakes. You won`t regret it!!
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Old 11-16-2012, 03:52 PM   #53
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Not such a stretch as comparing Motor homes to Air liners and heavy haul mine trucks.
I only quoted an article about them, I didn't say I'd rather have that mine trucks brakes over the ones Ford put in my m/h.

The reference to an airliner (by someone else) was to demonstrate that, like with mining equipment, some of the biggest, heaviest, most robust braking systems out there, bar none, are hydraulic, not air systems.

as was posted by another earlier on, you find air brakes on large motorhomes because they are what that chassi uses in other applications and because it's the most commonly found system on transport trucks which make them easy to fix and get parts for, not because it's the best system there is.
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Old 11-16-2012, 05:20 PM   #54
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The original poster asked if he should get an air brake endorsement. He has got some good advice and a bunch of crap. I hope it does not put him off asking another simple question
Your input was very informative, all the rest is crap. Ok.
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Old 11-16-2012, 06:25 PM   #55
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If that is what you got out of that, ok but I thought there were several other posts that answered the question asked by the original poster.
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