The brakes on my 1992 Breakaway are "air over hydraulic". If I were to lose all air pressure on one side only, would I have an adverse affect in trying to stop without my brakes grabbing on the side that lost the pressure?............

Of course, if you lost brakes entirely on one side, in-line braking would be impossible. But, I don't know how that could happen. The two tanks are not for left and right. As I understand it, one tank is practically a reserve tank.

The air over system is not side to side but front and back the two tanks ae charged so that they are relatively independant. If you start the engine with no air in the system you should note that the rear gauge will show charge up to about 60-70 psi. before the front will charge up, then they will both charge together to around 120 psi.

Losing air would cause the "E" brake to apply. The "E" brake on an air over is usually on the rear drive line and arrached to the transmission.

The front calipers are driven by one air/hydraulic master and tank, and the rear calipers are driven by the second air/hydraulic master and tank. The tanks are a single tank with a divider in the middle so there are two separate sections..

I was reading the following about true air brakes back in Feb. and saved the links: http://www.rvforum.net/joomla/...ech-topics&Itemid=45

http://www.rversonline.org/ArtAir.html

http://www.rainbowrv.com/rv-ta...r-parking-brake.html

Mogan & Ed: A sincere thanks. I got it........

Thanks---everybody should read these links!!

Good information BUT, I strongly disagree about "slight pressure " on the brake peddle going down a grade. If you are in a lower gear which you should be, your engine RPM will be high and the air pump will be able to keep up with brief but firm applications. Riding down a grade with a slight brake application is setting yourself up for brake fade. I use the speed posted for trucks as a reference and when my target speed is 5 MPH above taret speed, I apply the brakes firmly to get back to the target speed. I repeat this process down the grade unil the grade levels off.


The air supply tanks on my Breakaway are small but I have never even come close to runnung low on air pressure.. The two grades that I take frequently are the Grape Vine and the grade out of Laughlin NV.


Of course it is essential that air pressure is monitored during these conditions just as monitoring engine EGT and temperature going up a grade.

Good catch Ed!

This article backs you up;

Downhill Braking

Snub don't ride!
•Some drivers don't understand the severe demands put on the brakes by long downhill runs. Suppose your doing 6 miles with an average 6% downgrade. Runs like this are common out west. (In the east too?) This is a 1900' change in elevation. A free fall from 1900' results in a terminal velocity of 238 mph- neglecting air resistance. This would be the velocity of your rig -neglecting air and rolling resistance- if you didn't brake.

•Negotiating this grade is the same as slowing down from 238 mph. This is like 16 stops from 60 mph (not 4, kinetic energy varies with the square of the speed: (238 x 238) / (60 x 60) = 15.74 ) Suppose you average 30 mph coming down, the run will then last for 12 minutes. Sixteen stops from 60 mph in 12 minutes is a lot of stopping. Obviously your brakes had better be right and you had better use the right braking technique if you want to make it safely to the bottom.

•In recent years there has been some erroneous information going around about how to brake on long downhills. It was suggested not too long ago that a continuous application of the brakes as opposed to intermittent application or snubbing was the preferred method. THIS IDEA IS COMPLETELY WRONG!

•The proponents of the old theory have rescinded it, there is now (almost) universal agreement that the proper way to brake on a downgrade is to intermittently apply all your service brakes in a way that will reduce the speed of a fully loaded vehicle by about 5 or 6 mph during each application. What is key here is not the speed drop, this will depend on weight, grade and other factors, but air pressure, you have got to get the application pressure high enough to get all your brakes working.

•In theory, it doesn't make any difference whether you ride or snub the brakes on the way down. The problem is that you don't drive a theory, you drive a truck. In theory, the same amount of heat is put into the braking system regardless of how you apply the brakes. In practice, unless your brakes are in good condition, tractor-trailer balance is right and the load is ideally located, the continuous application of the brakes is likely to result in uneven drum and lining temperatures and problems before you get to the bottom of the hill.

•Steady, low pressure application of the brakes may not cause all the brakes on the vehicle to apply and may result in some brakes -those with the lower activation pressures- doing more work than others. Specifically, in many cases the tractor brakes will do too much of the work while the trailer brakes loaf and you might then get fade at the tractor axles.. Other brake problems can be aggravated by the low and steady braking technique. What you want is all the brakes working some of the time, not some of the brakes working all the time. The application pressure must be high enough to ensure that all brake chambers apply and that all linings make solid contact with the drums - about 20 psi or higher.

Yup. Riding the brakes is bad. An old truck driver told me that forever ago, (said pretty much what Ed said) and it has been great advice. The next trip down the same mountain with the same equipment after his advice, there was no brake fade.

His exact technique was to pick a speed you like. As soon as you are 5 over, brake firmly down to 5 under. Repeat. With disk brakes, this lets cooling air get in between the pucks and the disks. With drums, it stops the heat generation for a while and keeps distortion down, as well as letting things cool between applications.

Sometimes, I will be following another RV down a mountain, and will see by his brake lights that he is riding his brakes. Sometimes, I can smell them, as well. Quite often, he will either pull over or get going scary fast.

It is even possible to fade P30 brakes by riding the brakes in stop and go traffic.

One more thing, with disc brakes, besides the obvious over heating/warping rotor and pads, there is a real danger of boiling the brake fluid in the calipers. This can have long term effects on the entire system. Air over hydraulic has these same issues as a power brake system in the P30 or any other hydraulic only system.

The reasons that the Breakaway uses air over hydraulic system is with a diesel there is no vacuum source available and the power steerinng hydraulic system is much lower pressure than would be needed for a hydro-boost system.

quote:

Originally posted by MWrench:
with disc brakes, there is a real danger of boiling the brake fluid in the calipers. This can have long term effects on the entire system.

What are those effects?

BTW, Ed, since you seem well-informed on BMWs, I was speaking with a neighbor who has a late BMW. I asked when they recommended changing the brake fluid. He said it would come up on his instrument panel if it needed changing. Does that sound right?

My BMW bike manual says annually.

My own sense is annually for hard or downhill drivers, and bi-annually for sedate flatlanders.

quote:

What are those effects?

BTW, Ed, since you seem well-informed on BMWs, I was speaking with a neighbor who has a late BMW. I asked when they recommended changing the brake fluid. He said it would come up on his instrument panel if it needed changing. Does that sound right?

My BMW bike manual says annually.

My own sense is annually for hard or downhill drivers, and bi-annually for sedate flatlanders.

Bill,

I just had my R1200GS done as I sure didn't want the expensive ABS unit to gum up.

Hard braking doesn't affect the fluid, but continuous exercising the system introduces moisture into the fluid. Moisture can enter through the reservoir (despite the vapor barrier), it can permeate the brake lines over time. It sounds improbable, but do you want to gamble. As far as once a year, that may be excessive. I remember we had this discussion around the color of the fluid and you and I kept a good look at the fluid color. I think that still works and an arid environment would preserve the fluid longer.

the reason I suggested an annual change for hard drivers or downhill drivers is that they work their brakes harder, and are more likely to need a fairly high wet boiling point. Brake fluid absorbs moisture with time and rain exposure.

A sedate flatlander would be unlikely to get his brakes hot enough to boil, even if the fluid had absorbed over a year's worth of moisture.

And, of course, some of this depends on moisture exposure and the initial quality of the brake fluid. Better fluid stays safe longer.

Bravo for this life saving info in Canada we are compelled to get an air endorsement not withstanding the thousands it could cost one if you compound your brakes that is engage your brakes while park brake is on,mucho pressure.wally 34ft monarch van isle

quote:

Originally posted by Mogan David:
I was reading the following about true air brakes back in Feb. and saved the links: http://www.rvforum.net/joomla/...ech-topics&Itemid=45

http://www.rversonline.org/ArtAir.html

http://www.rainbowrv.com/rv-ta...r-parking-brake.html