Journey with Confidence RV GPS App RV Trip Planner RV LIFE Campground Reviews RV Maintenance Take a Speed Test Free 7 Day Trial ×

Thread Tools Display Modes
Old 02-09-2015, 02:38 PM   #1
crazycal's Avatar
Join Date: Feb 2007
Location: NUNYA
Posts: 4,236
Year: 1995
Coachwork: Thomas
Chassis: 3800
Engine: DT408, AT545
Rated Cap: 23 500 gvw
Air brake question.

When air brakes are set, does it lock the brakes on both axles or just the rear?

I'm hungry!

You Gotta Let Me Fly
crazycal is offline   Reply With Quote
Old 02-09-2015, 02:45 PM   #2
Bus Nut
Join Date: Jun 2013
Location: Southern Maine
Posts: 337
According to this article the rear are spring loaded and the front are not. Bold and Underline are me helping to point to relevant info.
Link if you would like to read the whole article.

The parking valve is typically located on the dash. With normal system pressure, pushing the valve “in” causes air to flow to the parking (emergency) side of the double air chamber, retracting the push rod against its applying spring and releasing the brakes. The parking/emergency system is spring applied and air released. The push/pull dash parking valve is unique in that once the supply pressure drops to the valve’s internal setting (generally between 20 and 45 psi), the valve will automatically pop out, thus fully applying the rear spring brakes. In an emergency, the parking valve can be manually pulled out at any time, and rear braking will be experienced. In addition, the parking valve may be manually pulled out at any time in an emergency, and again, braking will be applied to the rear brakes. Understanding that the parking/emergency brake system uses the bus’ rear brakes and that it takes air pressure to release them explains why a bus that has not been used for an extended period of time and has lost air pressure will have heavy brake drag until there is sufficient air pressure buildup to cause the rear brakes to fully release. Always wait until the warning buzzer is off before moving. All buses built in 1975 and thereafter have a dual brake system. One system operates the front brakes, while the other system operates the rear brakes. These systems can be readily identified by the presence of a single gauge with two needles. (Two single-needle gauges are also used.) In dual systems, should air be lost in the front system, the rear braking system will stop the bus. Conversely, should the rear brake air supply be lost, through special valving, the rear spring brakes’ release air will be bled off in direct proportion to the front brake application air pressure, thus stopping the bus normally. In either of the above cases, the low-air warning systems will be activated due to low air pressure in the failed system; however, the bus can be safely pulled to the side of the road and stopped.
Malkieri is offline   Reply With Quote
Old 02-10-2015, 11:01 AM   #3
Bus Geek
Join Date: May 2014
Location: West Ohio
Posts: 3,709
Year: 1984
Coachwork: Bluebird
Chassis: International 1753
Engine: 6.9 International
Rated Cap: 65
All the above is correct. Park brakes are usually only on the rear and are spring activated and air released. Unlike in passenger cars and trucks, the rear brakes in busses are larger and usually end up doing more work. The special valving that they're talking about is the SR-7 valve from bendix.
Booyah45828 is offline   Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

» Featured Campgrounds

Reviews provided by

Powered by vBadvanced CMPS v3.2.3

All times are GMT -5. The time now is 05:10 AM.

Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2024, vBulletin Solutions, Inc.