[HoosierDaddy]

Here is an excerpt from the Indiana CDL booklet on air brakes. It might be helpful:
Procedure to check air brake system-
Begin with air pressure at or below 90 psi.
1. Let air pressure build and check that the governor cuts out between 100-140 psi.
2. Turn the engine off, turn the key to the "on" position so gauges work and release all brake valves. Fully apply the foot brake to see if the air pressure drops no more than three pounds in one minute.
3. Fan off the air pressure by pumping the foot brake to see if the low air pressure alarm activates at approximately 60 psi.
4. Continue to fan off the air pressure. At approximately 20-45 psi the spring brake push-pull valve should pop out.

If you would like to learn more stop by your BMV office and pick up a CDL manual. (they are free in Indiana) Even though a CDL is not required for RV's there is a lot of useful information in the manual.

In order to prevent possible brake damage do NOT depress brake pedal while the Parking brake valve is activated. (Pulled out)

[rheavn]

That is great info! I wonder if the CDL manual is available online?

Thanks.........................

[encantotom]

i didnt know about not depressing the brake pedal when the parking brake is pulled out.

thanks dean

tom

[Ozarkguy]

This is the manual I have been studying. Air brakes start in section 5.

AZ 40-7802.pdf Size: 4.04 MB  Downloads: 19

[Mxfarm]

Keep in mind the e-brake chambers and the service brake chambers while independent are housed in one unit. The diaphragm in the service brake side is simple to change ( outside of the sealed units ). If your air pressure leaks down while holding the brake pedal down - that's your issue.
-However- while the e-brake side uses a similar diaphragm it also incorporates a rather impressive spring which if released and not contained properly can result in severe injury.

[77newell]

Tom: regarding not pressing the foot brake when the parking brake is on. In some brake configurations this would cause the spring brake (parking brake) and the service brakes to combine forces which could overstress the brake mechanisms. This was according to the manual I studied in preparation for the CDL for farm use recently.

With our more modern brakes this isn't a problem. I step on the brake every time I release the parking brake and nothing untoward has happened yet.

[HoosierDaddy]

77 Newell is correct. Modern systems are protected from damage. I added that note just in case there are Newells on the road that still have the older systems in place.