Slow Compressor

[Stretch]

Just a thought about the air pressure on the brakes. Are not the rear brake chambers dual? Meaning one chamber uses air to provide clamping power. The other chamber houses a giant coiled spring. If you lose all or most of the air in the one changer, the other with the spring will automatically apply the clamping power and stop the coach. Correct?

[Mike Canter]

Ross, I was under the impression that air brakes worked when you took the air pressure away. Don't know about a dual chamber. Yes, if you lose air pressure and it gets below 25 psi the DRIVE axle brakes will apply. The fronts will not.

[moisheh]

In every Canadian province you must have an air brake endorsement to drive ANY vehicle equiped with air brakes. This should be law in every state as well. Here is a link to the air brake manual for Manitoba. I think it was actually written by the BC government and has been adopted throughout Canada


http://www.mpi.mb.ca/PDFs/AirBrakeMa...ManualComp.pdf

The rear brake pots are dual chamber. One chamber is normal and is applied with air pressure from the foot pedal. The other chamber is larger and has a huge spring that will apply the brakes if the air from that chamber is exhausted. When you apply the Park brake that air is released. If the pressure in that chamber drops to below 35 lbs. ( as in a severe air leak) the brake will be applied. When you must be towed the tow truck driver will either connect an air line to your system or "cage" the rear air pots. This is done by compressing the spring via an external stud. NOTE: Do not fool with air brakes. That rear chamber is very dangerous. I should rephrase one of my statements. I really think that no person should be able to drive a large MH without a special license. Not a CDL but something that shows you can handle the vehicle properly. I know that Americans don't like Gov. interference ( me neither) but this is a safety issue.

[Mike Canter]

Great manual, now I got to sit down and read it all. (and stay awake)

[Stretch]

Mike: Moisheh has it right. The dual chamber in the rear needs air pressure to apply the brakes. If you loose the air the other chamber with the giant (and very dangerous) spring will aply the brakes. That spring also acts as a parking brake.

[Mike Canter]

At least I did know that if you lost air the drive axle brakes apply. I test that on a routine basis. Now I have that manual to read I am going to be dangerous. I did already have just Chapter 8 out of it.

[Papa_Jim]

Moisheh,

You are exactly right about needing air brake endorsement in Canada. We live in Manitoba. When we bought our coach, we were not able to drive it all until we had passed our written and practical air brake endorsement tests.

In Canada, if an accident is caused by air brake failure, the driver of that vehicle is held legally responsible. It is a legal requirement that the driver of any vehicle with air brakes goes through all the examinations and tests to certify that the air brakes are functioning 100% correctly.

I really do think that everybody, everywhere should have to take this test before they get behind the wheel of any vehicle with air brakes.

Air brakes function differently than automotive hydraulic brakes. The air pressure releases the brakes. Loss of air pressure engages the brakes.

[sdennislee]

Everyone reading this thread should read and print post number 8 by Mike. Laminate and keep it with you until its second nature.

[sc3283]

Shouldn't everyone know how their brakes operate be it air or hydraulic? Auto, truck or RV?

[OnJa]

Mike, what happened to procedure #7 in "Test One"?

Originally Posted by Mike Canter

Rick, here are two different air system and brake tests. See if your MH can pass them.

Test One
TESTING YOUR AIR BRAKES AND SLACK ADJUSTERS
Auto slack adjusters are used to maintain proper brake chamber stroke and lining to drum clearance during normal operation.

The entire slack adjuster operates as a unit rotating with the brake camshaft as brakes are applied or released.

THE MOST EFFICIENT BRAKING OCCURS WHEN PUSH ROD TRAVEL IS HELD TO A MINIMUM.

Auto Slack Adjusters adjust themselves automatically during full brake applications to accommodate brake lining and drum wear. The key words here are FULL BRAKE APPLICATIONS.

Have you ever engaged your brakes full.... pedal to the floor... probably not many have. But there is way to do this properly to ensure you get your auto adjusters to work for you. If you have never fully depressed this pedal it is likely that your auto adjust system has not been fully activating its full adjustment potential.

DO NOT RUN OUT AND DO IT NOW....DO THE FOLLOWING PROCEDURE TO ENSURE THE SAFETY OF YOUR BRAKING SYSTEM AND THAT YOU DO NOT DAMAGE IT.

Following is a procedure that should be done every day before you start your drive. Certainly, it should be done if your unit has been sitting for a time without use. This will tell you if your air brake system is functioning satisfactorily and will also adjust your slack adjusters.

1.Start engine and let air pressure build up.

2.Block wheels (use chocks that can be purchased from an RV supply store and chock the outside dual on each side. Be sure to insert a chock in front and behind the tire to ensure no vehicle movement. Parking on level ground when you do this is a big help. After this is done and you are sure your Discovery can not move RELEASE YOUR PARK BRAKE.

3.Your brake pressure should be at max. Now fan your brakes to
85psi. NOW ENGAGE YOUR PARK BRAKE AGAIN. Compressor should cut in and watch to ensure a return to full pressure.

4.When you have reached max pressure and the compressor has cut out RELEASE YOUR PARK BRAKE AGAIN AND SHUT OFF THE ENGINE.

5.MAKE FULL BRAKE APPLICATION (BE SURE you have released your park brake before you do this or you will damage the system.) Hold the pedal all the way to the bottom for one minute. Watch your air gauges as they should not move (allowable loss in this mode for 60 seconds is
3 psi). Listen for audible leaks as you wait for the 60 seconds to expire. After 60 seconds release the pedal. (YOUR AUTO SLACK ADJUSTERS WILL SET UP AUTOMATICALLY DURING THIS PROCEDURE.)

6.Turn on key... fan brakes to 20 psi. LOW AIR WARNING SHOULD START, continue to fan down to 20psi.. by now your park brake will have engaged automatically although you will not have any indication of this. Start engine and run at 1000 rpm using your cruise setting. Time
3 minuets. In this time your air pressure should be up to between 50 and 90psi. This will tell you your Compressor is functioning properly.

8. Apply park brake.

End of Test One

TEST TWO

Brake System Check Procedure

(Note- Damage can occur to your service brakes if pedal is pumped hard while Park/Emergency brake is engaged.)

• Be sure rig is on level ground and/or use chalks
• Start the engine. Let the air pressure build up until the governor activates the air compressor cut-out release of air at about 120-130 psi.

Check the Air Compressor Cut-Out and Cut-In Function

• Release the emergency/parking brake.
• Press the brake pedal several times until you see the needle drop to around 85-90 psi.

At that point the governor should activate the air compressor cut-in and the pressure should build back to 100 psi in about 45 seconds.
Allow the pressure to build to cut-out at about 120-130 psi.

Check for Air Leaks

• Shut off the engine, but leave the ignition in the "on" position.

Watch the gauge for one minute - there shouldn't be more than a 2 psi drop in pressure. (This checks for leaks from the air compressor to the tanks and the one-way check valves.)

• Press the service brake (brake pedal) and hold it down for one minute. There should be no more than a 3 psi drop in pressure. (This checks for leaks with the system under pressure: the air lines, one-way check valves, and Diaphragms.)

Check Audio and Visual Low Air Pressure Alarms/ Adjust Auto Slack Adjusters

• Turn the engine back on and let the compressor build pressure to the air compressor cut-out.

Turn the engine off but leave the ignition switch on.
Smoothly pump the service brake pedal until the low air warning light and buzzer activate. Devices must activate at not less than 60 psi.

Check the Emergency/Parking brake Function

• Continue to pump the service brake pedal until the emergency brake pops out automatically. Application should occur between 20-45 psi.

• Start the engine and allow the air compressor to reach cut-out level.

Remove any wheel chalks.
Shift into gear.
Apply your accelerator, but not over 1000 RPM.
Your Rig should not move.


NOTE: Slack Adjustment

Ensure reservoir air pressure is above 90 lbs on both air tanks and make a FULL brake application and release (Hard application to the floor). Repeat this process 6 times. (These brake applications will be adequate to cause the automatic slack adjusters to adjust)

Note: A light brake application will not cause the adjustment

[OnJa]

Originally Posted by Mike Canter

Rick, here are two different air system and brake tests. See if your MH can pass them.

THE MOST EFFICIENT BRAKING OCCURS WHEN PUSH ROD TRAVEL IS HELD TO A MINIMUM.

Auto Slack Adjusters adjust themselves automatically during full brake applications to accommodate brake lining and drum wear. The key words here are FULL BRAKE APPLICATIONS.

NOTE: Slack Adjustment

Ensure reservoir air pressure is above 90 lbs on both air tanks and make a FULL brake application and release (Hard application to the floor). Repeat this process 6 times. (These brake applications will be adequate to cause the automatic slack adjusters to adjust)

Note: A light brake application will not cause the adjustment

If you will slightly apply pressure to your brake pedal [not to stop but causing a drag to your brake pads or lining] while backing up, it will adjust the slack adjuster element in each of your brake chambers to where all brakes are evenly adjusted causing your vehicle to evenly decrease speed and not pull Left, Right, Dip nor Squat.

[Mike Canter]

Onja, there is nothing in any air brake manual or data that I have that states that you can adjust the slack adjusters by backing up on a 100% air braking system. I have not seen anything in the design of a air brake "Automatic Slack Adjusters" that will make that happen. I am interested in where you learned that trick. Maybe that works in a Air-Over-Hydraulic braking system but not in a 100% air braking system because the slack adjusters on a 100% air system do not have any provisions that I can see to allow adjustment in reverse with slight pedal pressure. You might find Chapter 8 of the Air Brake Manual that Moisheh so kindly posted has a real good description of Automatic Slack Adjusters.

I know that is how you adjust a shoe brake on a car because there is a cable and pawl attached to the adjuster to do that so since an Air-Over-Hydraulic system has regular hydraulic brakes then I assume that would work with that type of system only.

I think Procedure #7 missing was my keyboard messing up.

[DieselOne]

The compressor on my cummins seemed to take along time to build up pressure. Turns out it was the reed valves in the compressor head. A spec of debri got under one valve (very tiny) and it did not seat properly. A simple cleaning cured the problem, but you may want to replace the reeds when you have it apart or have it serviced. Good luck with your pressure issue.

[moisheh]

jimkate: Hi to a fellow Manitoban. You stated that air pressure loss is what applies the brakes. I hope you meant to say: "The dual chamber will apply the rear brakes when the air pressure drops below a certain safety level." The brake chambers normally operate by applying pressure to the chamber. Opposite of what you posted. Onja: There is nothing in an auto slacks air brake system that works by driving in reverse. The slack push rod is where the brakes adjust and vehicle direction should have no bearing on how the slacks work.