Hydraulic or Air Brakes?

[J3PO]

Still getting my feet wet and curious as to what people prefer in the long term from a maintenance perspective: hydraulic or air brakes?

[oricha1984]

I'm a new noob here, but from what I've read. Air >hydraulic

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[NowhereFast]

There's a reason big rigs have air brakes!

[J3PO]

Originally Posted by NowhereFast

There's a reason big rigs have air brakes!

Touché - thank you

[Tootalltechie]

Where I live (BC Canada) need a special addition to my license for air brakes so I went with hydraulic brakes on my bus.

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[Mark_In_MA]

Don't automatically be fooled by big-rigs use of air brakes. There are plenty of pros and cons about the systems.

Air brakes were first used on trains (in part because trains were designed/constructed first.) Air is used because it's many things - but not not exactly because it's best. The biggest thing about it is that it's free - it's everywhere. If it leaks, no problem - you can get more! You don't need to clean it up if it "spills." It has little weight to it, and it's fairly easy to filter out contaminants (like water.)

Many of the same things can still be said about trucks and trailers - you pick up a trailer that's been sitting around a few weeks, and you just fill the air tank back up again, and away you go. But air is picky - it needs to be dry, if you get water in the system, you can get ice, and things will freeze up.

Air has one BIG advantage - the first brakes were manual - no power assist. That was okay for something like a car. For a truck, you need a bit more force. So you have power-assist brakes - which use engine power to assist your stopping power (vacuum, or hydraulic.) That's great - IF the engine is running. If the engine stops, your power assist goes away - and so do your brakes. The tank of pressurized air sitting under the truck cab doesn't care if the engine is running or not. You've got a fairly long time to get the truck stopped, using the stored compressed air.


What still matters in the end is the ability of the brake system to dissipate the heat generated from friction to stop the vehicle - whatever generates the pressure is secondary.

I mean, we use both pressure systems all the time - air-powered jackhammers and tools, but hydraulic excavators and tractors.

[cadillackid]

I'll tell you soon.. I have a bus with air brakes and just bought one with hydraulics so i'll soon know the pros and cons of both!

-Christopher

[tad875]

Originally Posted by cadillackid

I'll tell you soon.. I have a bus with air brakes and just bought one with hydraulics so i'll soon know the pros and cons of both!

-Christopher

Any word on your findings?

[J3PO]

Originally Posted by cadillackid

I'll tell you soon.. I have a bus with air brakes and just bought one with hydraulics so i'll soon know the pros and cons of both!

-Christopher

Very interested to hear!

[cadillackid]

I drove both busses one right after the other...
1. AIR Brake - in a hard stop scenerio I can get from seeing the need to stop to braking going to the wheels faster with the air brakes.. maybe 1/2 second to maybe 3/4 second. but thats the difference sometimes in crash vs stop..

2. HYDRAULIC -that good familiar feel of regular car brakes.. more pedal travel... easing into the pedal.. unlike air brakes where you have very little travel... so with hydro you have that car feel.

3. AIR BRAKE - Precise control in slick conditions.. - this one from a situation a few weeks ago where a car pulled in front of me in the rain... it was Very easy to feather the pedal in and out quite quickly to pulse the rear wheels so they didnt stay Locked up... with hydraulic the long slower pedal travel would not allow for pumping.. of course with the air theres the chance you will outpump the compressor and run the pressure low.. but I still had 75 PSI at the end of that stop.. and my bus didnt go sideways in the rain..

4. AIR BRAKE - Failsafe. with an air brake you have an extra braking system that is not present on hydraulic.. that is your rear spring brakes which apply during loss of air pressure... they are REAL brakes.. that also act as a parking brake so 4 wheels in the back t hold it stopped when parked. with hydraulic you often have a single brake on the driveshaft.. which would be tugh to stop a bus in a failure but is fine as a parking brake.

5. Hydraulic brake - ease of repair... typically 2 or 4 wheel disc very similar to car brakes.. so you can likely fix most things on them yourself, or a normal car shop with a big bay can work on them... whereas air brakes take specialized tools and specialized knowledge only big-rig ($$$) shops have..

6. Air Brakes - They just plain Sound Bad-Ass!!

-Christopher

[cadillackid]

Originally Posted by NowhereFast

There's a reason big rigs have air brakes!

the BIGGEST reason is because of the coupling to the trailer...

if all of the brakes were hydraulic it wouldve been a lot harder to couple and uncouple a trailer if all on one system.. imagine having to bleed hydraulics every time you hitched up

one couldve used electrically actuated hydraulic brakes... however brake controller technology didnt exist when big rigs were conceived and air brakes designed...

-Christopher

[jazty]

Originally Posted by cadillackid

6. Air Brakes - They just plain Sound Bad-Ass!!

Can't argue with that one!

[Tootalltechie]

1 question, Was the hydraulic brakes vacuum boosted or Hydro boosted?

[Scooternj]

Negative for hydraulic brakes- Most brake fluid is hyrdoscopic, which lowers the boiling point of the fluid. See this white paper in it.

[cadillackid]

Originally Posted by Tootalltechie

1 question, Was the hydraulic brakes vacuum boosted or Hydro boosted?

they are hydro boost with a backup electric motor that operates the assist in case of engine failure.
-Christopher

[Tango]

Originally Posted by cadillackid

they are hydro boost with a backup electric motor that operates the assist in case of engine failure.
-Christopher

That is the same system I am building onto my rig. The master is from a mid sized International truck. Hydro with 4 wheel disks is plenty for my little 8000 pound shorty.

[cadillackid]

i stand corrected on my hydro brakes in the new bus.. im told all bluebird internationals are 4 wheel disc.. I couldnt tell exactly on my rears but thought it almost looked drum.. but I guess in 2000 it was not dont that way anymore so I probably have disc on that hydro bus.
-Christopher

[Mad Mel]

Originally Posted by Mark_In_MA

Don't automatically be fooled by big-rigs use of air brakes. There are plenty of pros and cons about the systems.

Air brakes were first used on trains (in part because trains were designed/constructed first.) Air is used because it's many things - but not not exactly because it's best. The biggest thing about it is that it's free - it's everywhere. If it leaks, no problem - you can get more! You don't need to clean it up if it "spills." It has little weight to it, and it's fairly easy to filter out contaminants (like water.)

Many of the same things can still be said about trucks and trailers - you pick up a trailer that's been sitting around a few weeks, and you just fill the air tank back up again, and away you go. But air is picky - it needs to be dry, if you get water in the system, you can get ice, and things will freeze up.

Air has one BIG advantage - the first brakes were manual - no power assist. That was okay for something like a car. For a truck, you need a bit more force. So you have power-assist brakes - which use engine power to assist your stopping power (vacuum, or hydraulic.) That's great - IF the engine is running. If the engine stops, your power assist goes away - and so do your brakes. The tank of pressurized air sitting under the truck cab doesn't care if the engine is running or not. You've got a fairly long time to get the truck stopped, using the stored compressed air.


What still matters in the end is the ability of the brake system to dissipate the heat generated from friction to stop the vehicle - whatever generates the pressure is secondary.

I mean, we use both pressure systems all the time - air-powered jackhammers and tools, but hydraulic excavators and tractors.

Just a clarification on "AIR" brakes. The air does not apply the brakes. A huge spring in each s-cam actuator is what is applying the brakes. The air is releasing the spring pressure via a diaphragm. So no air in the system no move. There is no separate park brake system with air brakes. When you apply the park brake it dumps the air from the system and lets the springs do their job.

[Mad Mel]

I have been a medium duty bus tech for decades. I always worked on juice (hydraulic) 4 wheel disk brakes for the most part. I just bought my first School bus and it has air brakes. Its a 34' Freightliner Thomas. My fleet vehicles are 34' Freightliner tour buses with hydraulic disk. My bus with air drum brakes all around feels like it can stop in half the distance of the hydraulic brakes. They feel sooooo much more confident in a heavy vehicle. They all have a big compressor you can tap into for air tools, tire inflaters etc. They usually always have air ride suspension on the rear that auto levels to what is needed. Beats leaf springs all to hell. The drivers seat is often a cushy air suspension seat. Great for long drives.



Also folks an air brake endorsement on your general license is not that big of deal. In Alberta it's a two day course you can take on a weekend and your done. Here is a HUGE secret most skoolie folk don't seem to realize. Air brake buses don't get bid on because everyone thinks getting a Q endorsement is a hassle. I put the minimum bid on this pretty cherry 2007 and got it with no other bidders.

[cadillackid]

Air very much does apply the service brake. The spring applies the rear park brake or I’m the event of air loss the rear springs will progressively apply as an emergency stop..

The service portion of the chamber and the front chamber apply from positive air pressure..


To clarify power assist in hydraulic brakes, the emergency electric motor maintains powder assist in the event of engine failure .. you don’t lose power brakes when the engine stalls provided your system is maintained .. ie you test the power assist motor periodically and maintain good batteries ..