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2004 ISC 8.3 Pacbrake Mechanical and electrical/air testing method


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New to us MH. I thought Pacbrake was working until I tried it on a short 5% grade and RPMs climbed very quickly. Previous owner only drove 4k miles in 4 years. These lock up if not used often. Some of these pictures I previously added to another post on Pacbrake repair. As this includes a method to activate the solenoid to test the brake, I have elected to start a new topic. 

I found the Pacbrake valve lever very stuck in the open position. Managed to get a small screw driver between the lever and pin to rotate the lever a bit. soaked both clevis pins, cylinder rod, and valve shaft with the Pacbrake oil. came back later and it was starting to move a little but no return by the spring (Pic 52). Oil, wire brush, moving the lever back and forth, more oil got it free and the spring would return it to the stop. Pacbrake has a good maintenance tech report. pulled the air supply hose and a squirt of oil into the fitting. Called Pacbrake tech department and asked if the solenoid had mechanical activation. Nope, 12 volt to the wires only.  My wires disappear under floor below the bed. I could not find anything that felt like a connector. 

Last night, I searched thru the electrical diagrams and found the two relays for the air solenoid and to activate the brake lights when the Pacbrake is on. The relays are in the Monaco 2 fuse/relay box in the front run compartment. Ex brake 1 and 2 relays. Relay 2 terminal 87 is the wire going directly to the Pacbrake air solenoid (pic 61 & 62). I cut half of the ring off a small crimp terminal, pulled off the insulation and inserted it into the slot that the relay would have plugged into. Part of the crimp fitting is visible in front of the green alligator clip. This was my connection to get power into the terminal associated with 87 on the relay. Connected 12vdc from the big fuse block above and I could hear the air going into the cylinder and the valve hitting the stop (pic 53). With the air solenoid energized and valve closed, I cleaned the cylinder rod off and relubed most everything. Cycled about a dozen times and checked that it was going fully open and closed. A note on the relay diagram in pic 62, terminals 85 and 86 are the relay coil, the line between 30 and 87a would be the NC contacts in what is called the shelf state, coil not energized. When the coil is energized, power is delivered from 30 to 87, which is why I supplied power to that terminal. The bottom of the relay tells what the pins are.

The fuse/relay box does not match up to the electrical diagram but the relays and fuses are labeled on the box. the darker yellow 20 amp fuse just to the left of the alligator clip is the supply to these relays. It was blown. I checked the current going to the solenoid when activated and it was 1.5 amps. Will replace the fuse later this week and go for a test run. I am a little concerned about how the fuse blew.  The solenoid is either on or off. The current does not go up if the valve does not rotate.

HRS pacbrake lube62.JPG

HRS pacbrake lube61.JPG

HRS pacbrake lube53.JPG

HRS pacbrake lube52.JPG

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I test my PacBrake every time I take the coach out.  I make sure to try the PacBrake and hear and feel it working.  I lube it about twice a year, last time actually took the air cylinder completely out so I could make sure everything was working. 

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Wife drove MH over weekend and I pulled up rear access panel to watch PacBrake in operation. It is working correctly and makes a difference in deceleration of the MH. I am so thankful we did not head off to Portland with the PacBrake not working.  I have seen posts that talk about a two stage exhaust brake. That got me to thinking that maybe those systems used a switch when off the solenoid would not function and you get the braking I had before with a non-functional PacBrake.  When the switch was on, full PacBrake. In the 1,000 miles we drove the MH b4 fixing the brake, the PacBrake was about right when running 65 mph down the hi way to slow just a bit. Anyone have experience along these lines? 

Have been reviewing electrical diagrams to see if there is a way to simulate the ECM asking for PacBrake to see if the brake lights are working. The issue is getting to the terminals with the relay in place. The only other way I can think to test is to have a follower in a car.

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Manually override the backup camera to stay on, step on the brakes and see if you can see the glow, then take a small drive at night, click on the pac brake and look to see if you can see the brake light glow.  

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