We(vol. fire dept.) have a M915 military truck( They are miltary, but use commercial driveline components for the most part) It is currently on the side of the road with the truck brakes locked up. The trailer we are pulling seems to be fine. The truck parking brake and trailer supply valves seem to be working fine. They stay in/out, & act normally. The foot brake petal, however acts funny. It feels different and when released, some air exists the valve through a vent or whatever at the top of the valve that exits throught the firewall. I tried caging the front drive brakes,(the rear truck axle brakes are different) but the truck still will not move. Does anyone have any idea of what could be wrong or any troubleshooting tips? Thanks Darrin
It's normal for a small amount of air to vent from the treadle valve when released. If it's a lot of air it usually means the quick release valve is gone but this should have no affect regarding the locked brakes. The treadle valve could be supplying air to the service brakes even though released - just crack a service brake line at a chamber to check. It's easy to do that on a front wheel chamber. On a commercial truck if this was the case the brake lights would usually be on as the brake lights switch is an air sender - on that maybe its not that way and might have a mechanical brake light switch. If there is air at the service line it's not necessarily the treadle valve. It could be something else sending air that way. And of course I know nothing about military trucks.
Not familiar with this tractor but one place to find the correct maintenance or repair is the TM manuals, being a new member my post limits are governed by the board. Try looking for TM manuals starting with this, TM 9-2320-273-10 and most of this is just operator information but there is over 17,000 pages online and over 20 TM manuals for this unit.
Try this Company.They might help you. http://www.memphisequipment.com/
If you are still having problems let me know, i have a CD on the 915
I finally got it to move. The park brake is working backwards. I had to leave the truck park brake on, and supply the trailer with air to unlock it to drive it. When you take the parking brake off the truck(by pushing the valve in) it sets the brakes and the brake lights come on. I still think it could be the treadle valve. Dt
It sounds like the truck has an anti-compounding valve. When you step on brakes it releases the parking brake. This is one of the places where service air and parking air come together. The problem has to be in a component where parking air and another air source are present and there is a failure. This might be helpful to explain anti-compounding: http://printfu.org/read/bendix-r-8-...Xj29K40djg3srnosfo3aTQ3tna4c3T5Lutq6acq6OHp-w
3. PARK BRAKES WILL NOT RELEASE: Step 1. Check reservoir pressure gage and verify LOW PRESSURE warning lamp is out. See Malfunction 1. Step 2. Verify PARK BRAKE manual valve is closed. Close valve; if valve will not close, refer to para 9-19. Step 3. Check air lines for leakage or damage. Use a soap solution to check for leakage at connections and watch for bubbles. Replace damaged lines and tighten loose connections (para 9-36).
3. PARK BRAKES WILL NOT RELEASE (Continued): Step 4. (M915, M916 and M920 only). Inspect intervehicle air hoses for proper connections. Connect hoses properly. Step 5. Check the air line between the two rear quick-release valves for damage or leaks using a soap solution. a. Replace the line if damaged and tighten connections. b. Replace the park brake quick-release valve (para 9-22).
I forgot to update this thread. There is a valve on the frame that was bad. It took a while to find a replacement. Thanks for all the help. Dt