Air Brakes VS Hydraulic Brakes...HELP!

mellalazy · 11-26-2016, 03:25 PM

Any advise on the differences?
We know that air brakes can sometimes require a CDL, depending on the overall weight of the bus. (Over 26,000 lbs in our state)
We've heard that air brakes can be far more difficult to maintain.
Is driving with air brakes much different than driving with hydaulic?

We've found a bus that is a beaut in all other facets...but the air brakes make me nervous.
Any helpful insight on this?

Much appreciated!

-Jess & Ben

Dapplecreek · 11-26-2016, 03:41 PM

I will not consider a bus with hydraulic brakes: I'm a full-on chicken, and want brakes that make you STOP when they fail, rather than making you keep going. [For folks who are unclear about air brakes: the first bit of pressure releases a 'spring brake' which locks up the wheel so it ain't going nowhere... if you were to blow a brake line it would lock up your back wheels and make the vehicle stop. This could be exciting if you were not expecting it, but a lot less exciting than stepping on your brakes and having them go to the floor with no deceleration, which is what happens with failed hydraulic brakes.]

So far as I understand, there is a bit different a 'feel' to air brakes but they're certainly easy to use. The hard part is for a noob to remember the details of the pre-trip checkout. Once you've done it a few times (and once you for-reals understand how they work) I would expect it to be about as hard as buckling your seat belt.

Also, a petite sort could stop the bus easily with air brakes: you're operating an air valve with your foot, not muscling the car to a stop as you are with hydraulic brakes.

Maintenance? I would think hydraulics would take more. You may be thinking of checking your brakes at the top of a hill: likely a good idea (or a requirement) for both.

If you're using your bus for recreation, there would be no Federal requirement for a CDL. Which state are you in? I think California wants you to pass that part of the CDL test to add an endorsement to your license. But you can do that.

mellalazy · 11-26-2016, 03:44 PM

We are purchasing in Colorado, but will eventually be moving to live out of it in California.

AlleyCat67 · 11-26-2016, 03:48 PM

The biggest thing when you drive air brakes for the first time is to resist the temptation to apply the same amount of pressure to the pedal as you do with hydraulic brakes.... properly adjusted air brakes are VERY sensitive to pedal pressure, and if you hit them with the same force as you do hydraulic brakes you're likely to be kissing the windshield.

Before venturing out into traffic, try to find an empty parking lot or somewhere to practice braking at varying speeds and pedal pressures, get used to how they respond and how much pedal force you need to stop within a certain distance at a certain speed. As you practice and get used to them you'll start to do it without even thinking about it.

cowlitzcoach · 11-26-2016, 03:54 PM

If your bus is registered as an RV you will NOT need a CDL to drive it anywhere in the US regardless of whether or not it has air brakes or hydraulic brakes. If you choose to travel into Canada, especially British Columbia, you will need to have an air brake endorsement on your license. B.C. has been getting really persnickety about air brake endorsements and they will red tag your bus if you don't have an air brake endorsed driver in the RV.

IMHO, air brakes are a much better choice for a bus conversion for the simple reason that they are extremely simple. Hydraulic brakes are a lot more moving parts that are swimming in fluid that is hydroscopic. As the fluid ages it attracts water that lowers the boiling point to the point where you can literally boil out your brake fluid to the point you have no service brakes at all. The water in the fluid also plays havoc on the metal parts inside the system. Wheel cylinders, master cylinders, brake calipers, and steel lines all have metal parts that will rust and ruin your brakes.

Air brakes, on the other hand, can sit for months or years and will rarely have a problem when asked to work again. As long as you drain any fluid out of the wet tank at the end of every day. Air brakes also usually have more braking surface and have the advantage of spring brakes for parking and emergency braking.

There seems to be a lot of mystery involved with air brakes. In actuality they are extremely simple. Think of stepping on the brake pedal like stepping on a long skinny balloon. As you move air from one part of the balloon to another it makes the other end of the balloon swell up. When you let up it goes back down. At each wheel there is what is not much more than an industrial strength balloon. You step on the brake pedal and add air into the system and it blows up the balloons and applies the brakes. You let off of the brake pedal the balloon shrinks and the brakes release. Easy, peasy.

IHMO, if the choice was between two virtually identical buses that are priced about the same I would go with the air brakes every time.

Tootalltechie · 11-26-2016, 03:56 PM

My 1974 bluebird has Hydro-vac brakes. It has 2 vacuum boosters frame mounted, with 2 vacuum tanks frame mounted. Vacuum boost is what most cars, vans and light duty trucks came with. Now cars, vans, & light may come with hydroboost brakes. The boost comes from the power steering pump. Where the vacuum boost came from the engine it's self. With bus and truck engines running low rpm the vacuum pressure was very low, so very little boost for the brakes. That's why air brakes came into being. A air compressor driven by the engine. Air brakes auto apply when the air pressure drops.

If I'm wrong please correct me.
Gordon

Sent from my SM-G530W using Tapatalk

cowlitzcoach · 11-26-2016, 04:06 PM

Hydraboost (sp?) started showing up when GM started offering diesel engines in cars and light trucks. Diesel engines have no vacuum to operate things like vacuum boosters. They also discovered that with all of the smog devices added to the engines the amount of vacuum available, particularly at low engine speed, was greatly diminished making the use of vacuum assist a bit of a problem.

Ford, Toyota, and others solved the lack of vacuum problems by installing a vacuum pump.

With the advent of ABS and virtually every car on the road having power steering it was easier to upgrade the power steering pump to power the brake booster than it was to add another pump into an already crowded engine compartment.

Most buses and medium duty trucks that have the hydroboost system also have an electric override that works when the key is off. The electric pump provides boost in case the pump fails or the engine dies.

Elliot Naess · 11-26-2016, 06:04 PM

No contest -- air brakes all the way.
But you REALLY SHOULD read up on them. Search this forum for links to good websites. But you can certainly find such sites yourself.

One thing that may not be mentioned in any educational material: Most air brakes have the pedal hinged on the floor -- as opposed to most other vehicles you have driven, where the pedal is hinged at the top under the dash. So you must apply force to the top of the pedal. This can take some getting used to.

Also, you must check the adjustment of the brake shoes from time to time. Many vehicles have "automatic" adjusters, but those malfunction routinely. You simply must check the adjustment yourself.

When you need to tighten "automatic" adjusters, know this: It is not possible to loosen them without disassembling them. So you must tighten only a tiny bit at the time and stop before it gets too tight.

With manual adjusters, you can turn the adjustment back and forth all you want. Make sure the locking collar pops out when you are done.

Come to think of it... I bet there are videos on YouTube demonstrating this.

Brad_SwiftFur · 11-26-2016, 06:55 PM

I believe you'll come to highly prefer air brakes, as I do. Maintenance isn't hard (taking the tires off simply requires large tools and some strength), the way the systems work is simple enough.

Some buses (as Elliot mentioned) have the pedals hinged near the bottom (typically flat-nose buses), so you'll apply the brakes towards the top of the pedal. Air brake pedals have relatively little travel compared to hydraulic brake systems. They don't need to. You're not "pumping" air through the lines. The pressure in the tanks does that for you. All you're doing is simply operating a pressure regulator (and essentially that's what the brake pedal is, little more than a foot operated pressure regulator), which works mostly based on how much pressure is applied. More (foot) pressure in = more (air) pressure out.

There is a little lag between the time you press the brake, and the time you actually get stopping effort, but with the way modern systems are designed, this lag is minimal and some people can't even sense it. Just be mindful of it when driving an air-brake equipped vehicle.

I posted a link elsewhere in this forum that is an old 60's U.S. Army video that is a pretty good explanation on how air brakes work. If you're interested:

Air Brakes: Principles of Operation - YouTube

Stu & Filo. T · 11-26-2016, 08:23 PM

I'm going to copy & paste something I wrote before on this subject.

This is my experience with hyd brakes, I drive a commuter van back & forth to work, 140 mile round trip carrying 13 other people with me. About 2 months ago I got on the road with the first 5 people I pickup then i drive to the next town over which is 6 miles away pulled off the freeway into the parking lot which is two stoplights off two stoplight back on.

I pulled into the lot came to normal stop the rest of the people get in I pull away, first stop light normal stop second stoplight which is also right turn on to freeway brake pedal goes to floor with no resistance what so ever, use parking brake to pull over & stop. Right front brake line decided right then to blow on me,no warning nothing, 30 seconds later I would have been up to speed cruising 70 mph with no idea I had a problem until i needed them. Only after pumping brake 3 or 4 time & fluid getting low did warning light come on.

Air brakes will warn you & automatically apply if theres a problem so IMOP get air brakes if possible.

Dapplecreek · 11-26-2016, 08:38 PM

Quote:

Originally Posted by mellalazy

We are purchasing in Colorado...

If you're shopping, keep an eye out for the word "retarder" or the phrase, "exhaust brake". These are devices which slow your bus using non-brake means. This allows you to go down a hill at a safe speed WITHOUT heating up your brakes. Some Colorado buses have 'em; most buses don't. They might add a bit to the price, but they might be very nice to have, especially if you plan to travel the Grapevine, go to Death Valley or up the back way into Yosemite.

AlleyCat67 · 11-26-2016, 10:04 PM

Not to mention the fact that there's at least one, and maybe two, air pressure gauges on the dash. So you'll see there is a problem before it gets to that point. The low air warning is supposed to come on at no less than 60psi, and the spring brakes automatically activate when it gets down to 25-30psi.

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