Air Brakes--- how to use

[Gary RVRoamer]

Using them is easy - push the pedal. There is a somewhat different pedal feel and a very, very tiny lag in application, but no big secret or technique.

You should, however, understand the brake system well enough to spot signs of problems and know what the warning buzzer means. Basically the brakes need a minimum of about 60 psi to operate and your brake system will warn you if nearing that limit. It will also give priority to the brakes over suspension and other air systems, for safety reasons. The air system can be compromised by moisture, so it will have an air dryer that extracts moisture. It requires occasional service (every 2-3 years), and there will also be manual air tank drains that may need occasional attention on older models.

[michelb]

As mentioned in the posts, there really isn't that much difference using the air brakes vs conventional (hydraulic) brakes except for the lag (which isn't extreme but I'd certainly describe it more than 'tiny' (like Gary did ). I think in a typical air brake system, you can easily get about 1/2 second of lag (i.e. from the time you press on the brake pedal, you don't actually start slowing down for 1/2 second so you have to take that in consideration and certainly adjust your following distance accordingly. To put that in perspective, at highway speeds, if you press the brake pedal, you'll travel about 30 feet before your brakes actually start applying (hence the adjustment of the following distances)).

What's more important is being able to tell if your system is working properly and having a base understanding of how it works (e.g. you can't drive with no air pressure, it's not safe to drive with less than 65 psi, you need to be able to tell if there's an air loss in the system, etc). You also need to know how your engine / exhaust brake works (if you have one - most motorhomes do).

[speedman42]

Thank you all so much for the advice. I just dont want to get into a bad situation and ruin our motor coach experience.
Again Thank You

[Brentw]

WOW, I do not post a lot, but this has my attention. Previous life- off road- non legal weight, mountain roads truck driving. There are some of the folks with a very good knowledge of air brake systems and quality driving (such as look far-anticipate others). Others really should invest in an air brake course in order to help them understand the system they are operating, not saying you have to be a mechanic to drive a big rig.

In British Columbia you must have an Air Brake endorsement in order to legally drive an air brake equipped vehicle, this should be every where. My 2 cents.

[jetfromtn]

Originally Posted by Dwight

NO! NO! NO! The brakes are applied by the amount of air that is applied to the empty air brake chamber located at each front wheel & each dual & single rear wheel. The amount of air is controlled by how far your foot pushes down on the brake pedal.

You are correct about the parking brake chambers located on the rear axle only. A coil spring applies the parking brake & air pressure is used to compresses the spring to release the parking brakes.
Dwight

You need to go back to How stuff works and check how air brakes work.

[dons2346]

Originally Posted by jetfromtn

The thing I had to learn is, the air holds the brakes open and when you apply the brake pedal it releases the air pressure and the spring closes the brake against the drum. Same thing happens when you apply the emergency brake, you release the air and the brakes close. It is completely opposite from what most of us are used to and there is a learning curve.

Jim Thompson
2007 Coachmen Pathfinder 384 TS
2007 HHR

You better read the manual in the link that Hooligan posted

[Wayne M]

Me thinks there is some confusion on the application of air brakes and parking brakes.

Here is a quote from the linked manual.

"Spring parking brakes may be installed on an air brake–equipped vehicle for use as a reliable parking brake system. In the service brake system, the brakes are applied by air pressure and retracted by springs. In the spring parking brake system, the brakes are applied by spring pressure and retracted by air pressure."

I don't think things have changed in principle, so here is a simple video that I found that may help in the understanding.

1967 Army Video on Air Brake System

[chuck49]

Dwight, Don, and Wayne are correct. The parking brake and the service brakes work exactly opposite of each other. The parking brake is operated by the "button" on your dashboard and the service brakes are operated by the brake pedal. When the parking brake is released, by pushing the button in, air pressure forces a heavy spring to retract. That spring was holding the brakes on the drive axle closed. When the parking brake is released a much smaller spring holds the brakes open ( on drum brakes). The brakes on the drive axle are typically the only brakes on the vehicle that have the dual function of both service and parking brake. If you look under the vehicle you can see that the brake cylinders (sometimes called the biscuit) on the drive axle are much larger than the ones on the front brakes. When all air pressure is lost or when the parking brake is applied, this heavy spring closes the brakes on the drive axle to hold the vehicle while parked. During normal driving air pressure holds the heavy spring in a retracted position keeping the parking brake or "spring brake " open. When you step on the brake pedal the service brakes are applied, or closed, by the applied air pressure in a proportionate manner. The harder you step on the pedal the more air pressure is applied and the harder the braking action. There is only one brake caliper or drum/shoes on each wheel. Not two sets os actual brakes. This dual function is accomplished with the brake cylinder. This is an over simplified description intended for a beginner sorry for the length. Hope I said it clearly. Make sense?

[gnrenfeld]

Two great write ups were posted on this subject. First was cooperhawk Post #13. I have as well 100,000+ miles in big rigs and that is my thoughts on driving a motorhome as well. I only have about 250,000 in Motorhomes but it applies to all units of any size and weight.
Secondly chuck49 post #22 done a great job of clarifying the operation of the air brake system.

[FormerBoater]

Lot's of good input here.

Especially on long downhill runs....use the tranny and the Pac Brake.

To the OP, main thing to understand is that while you have automatic slack adjusters on your rig, they must be calibrated on a regular basis.

If you feel that you do not have sufficient braking power, the slacks are likely in need of calibration. To accomplish this you need to find a level surface, parking brake off and fully stroke (pedal to the metal) your brakes six times for 30 seconds. If you roll down your driver's window you will hear the slacks calibrating (clicking) and voila...you will notice a big difference in brake response.

If you calibrate your slacks, you will find that your air brakes respond much like hydraulic brakes on your daily driver.

Also, do not depend so much on your Pac Brake to slow your vehicle down. Many motor homes have glazed brakes due to not enough use. The brakes are meant to be used....Spartan says that they have never seen brakes that were worn out in a MH application. If your brakes are glazed, find a vacant lot and do some hard stops from 15-20 MPH to remove the glazing.

DaveS
1998 American Eagle 40EVS

[rssnape]

Just to clarify the pedal feel, I don't think air brakes give as much pedal feedback as hydraulic brakes. It is relatively easy to push through to aggressive braking! For normal stops light pedal application will accomplish most of your stop. Aggressive braking will yield aggressive results. You better have your seatbelt on. My coach has a fair amount of nose dive during aggressive braking. So that panic stab at the brakes then realizing that you pushed too hard and releasing and reapplying sets up some porpoising that is scary. You really feel like you are loosing control.
Previous posts that say not to pump the brakes are dead on.

[Dogpatch]

Originally Posted by Wayne M

Me thinks there is some confusion on the application of air brakes and parking brakes.

Here is a quote from the linked manual.

"Spring parking brakes may be installed on an air brake–equipped vehicle for use as a reliable parking brake system. In the service brake system, the brakes are applied by air pressure and retracted by springs. In the spring parking brake system, the brakes are applied by spring pressure and retracted by air pressure."

I don't think things have changed in principle, so here is a simple video that I found that may help in the understanding.

That was a great video and well explains how the air brake system works! Thanks for sharing.

[Wayne M]

I thought so also Les.

Another item is to turn off the exhaust brake when in stop N go traffic (slow speeds) and when driving in a city with low speed limits, (35 mph and below) and lots of red lights. A continuous light pressure on the brakes will cause them to glaze over. By turning the exhaust brake off you will be applying more force to slow down or stop and this will aid in keeping the brakes from glazing.

Here is a kicker for you: The "emergency brake" applied by pulling the "yellow" knob. Many think that if you pull that knob you will come to a screeching halt. That is not the case, as anyone who has attended the Freightliner class in Gaffney, SC can attest. If you are traveling down the highway at 60 mph and pull that knob you will be able to steer off to the side of the road to stop. It will NOT throw you against the windshield unless you are standing up and off balance. It will gradually and rapidly bring you MH to a stop. Depending on the condition of your brake system, some MH's will stop a little faster. If you have to pull that button don't expect to stop suddenly.

Also, teach the passenger how to move the driver out of the way, release cruise control, pull the yellow button and steer the MH, should an emergency be encountered and the driver becomes incapacitated while driving and slump over the wheel. Heaven forbid that any one should encounter that, but just be prepared.

Happy trails.

[TRAILERKING]

Originally Posted by jetfromtn

The thing I had to learn is, the air holds the brakes open and when you apply the brake pedal it releases the air pressure and the spring closes the brake against the drum. Same thing happens when you apply the emergency brake, you release the air and the brakes close. It is completely opposite from what most of us are used to and there is a learning curve.

Jim Thompson
2007 Coachmen Pathfinder 384 TS
2007 HHR

Oh Boy here we go again with air brakes.
YOU SIR; I sure hope not to meet you coming down the highway......You have absolutely NO clue about the brake system (like so many on here). You've been educated wrong. One day you may hurt yourself or someone else. Just like Dogpatch stated, up here in Canada anyone that wishes to operate an air brake equipped vehicle must carry an air brake endorsement. Anyone that wants to operate an air brake vehicle study the "Air Brake Maunual". This wasn't just printed for CDL and Commercial drivers. Wake up people and take off your blinders.