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Old 04-25-2015, 02:03 PM   #1
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Sailor Fred's Avatar
Country Coach Owners Club
Join Date: Nov 2012
Posts: 28
Exhaust Brake Operation

My exhaust brake is not working. I can manually close the cylinder on the brake but cannot figure out how the solenoid works. Can anyone tell me how the solenoid on the air side of the exhaust brake works? Do I need the engine running to test the solenoid operation? One thread said I should be able to hear the brake operate but when I turn the key on and flip the switch to low the console light indicates the brake is working but I cannot hear the solenoid close. What air pressure is needed to make the cylinder operate?

A little background on my system. It has both a Hi and Low position.

The system works like this.
Cruise control must be off.
Put console switch on low, switch glows green.
Transmission does not downshift, not in circuit.
When you remove your foot from the throttle the dash light comes on and the exhaust brake closes.

Put console switch on high, switch glows green.
Cruise control can be either on or off.
When you remove your foot from the throttle, the dash light comes on, the transmission selects 2d gear and starts downshifting until it obtains second gear, and the exhaust brake closes. Once you reach 15 mph the PAC brake turns off.

1996 Country Coach
Magna #5342
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Old 04-25-2015, 05:47 PM   #2
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Join Date: Apr 2011
Location: Powell River, B.C.
Posts: 11,954
If the brake won't operate below 15 mph, you won't be able to check operation at idle or stopped.
My system only has one setting , like your high, and there is no air pressure reducer in the supply circuit to the solenoid , so I'm sure the actuator uses full system air pressure .
The solenoid acts as air supply to the actuator and vent to turn the pac brake off, and mine is controlled by a relay that is switched by an ECM output.
Many members have reported a damaged air supply hose between the solenoid and the actuator ; due to exhaust heat, so checking the hose is the first step. you could remove the solenoid and bench test. But first I'd want to have a full wiring diagram and schematics for your coach to make sure you know all the wiring and component location and operation. You could be dealing with something as simple as a blow fuse, in the relay supply circuit.
What chassis is your coach on ? Cummins or Cat, power?

99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.
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Old 08-10-2015, 08:25 AM   #3
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Posts: 251
On my 1993 manga, everything works off RPM's and throttle position. So when sitting still and idling, I can flip the dash switch, I can hear the air solenoid open, hear air escaping, and hear the brake close, I can see my RPM's reduce on the tach. As soon as I press the gas peddle, I hear the brake open, and solenoid shut air off.

When my brake stopped working, it turned out I had a broken throttle position switch (a pac brake item) it is a spring switch, it was replaced, a few trips later was broken again. I did not want to risk another broken switch so I purchased a lift gate spring switch at Napa and so far so good. It looks just like the pacbake version but much heavier duty.

Once I got the brake actuating, when driving down the road the and you head down hill, as soon as you let up off the throttle, your brake will turn on, you may be able to hear the air escaping, especially if you are running next to a cement divider. The more RPM's, the more braking. I believe I get max braking at 2000 RPM's, again for me it's not a speed function.

For me in an older coach I probably don't brake as well as a newer coach, because air braking utilizes your engine exhaust to slow the rig down, on older coaches the valve springs are probably not as strong as a newer engine is. Stronger valve springs produce better braking results. Some cummins engines with air brakes come with dual valve springs adding extra braking results. I was not getting very good results so I was researching what my problem could be, turns out when I was installing the new throttle switch, I noticed a ton, and I mean a ton of exhaust escaping right at the air brake. All my back pressure, which is my braking pressure, was escaping because of loose clamp that joins the brake to the exhaust pipe.

Once I tightened that clamp, it was like night and day. Our last trip to Washington towing a toad, there were Lots of 6% grades with little need for service brakes.
"Mrs. CC. Magna" 36' 1993 Country Coach, Magna, 300hp Cummins, 5 speed Alison trans. Acme Eze tow dolly with surge brake.
127,000 miles and counting...
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Old 08-10-2015, 10:15 AM   #4
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Country Coach Owners Club
Join Date: Jan 2006
Location: Sacramento Area
Posts: 3,229
I replaced the positive line into the exhaust brake with a cheater wire from the chassis battery.

Holding the cheater wire to the receptacle for the positive wire, the exhaust brake cylinder activated.

I can hear the back pressure of the activated brake with the volume control on the rear camera also when driving.
1995 CC Magna #5280
C8.3L 300hp Cummins, 31,000lbs
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Old 08-10-2015, 06:28 PM   #5
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Join Date: Sep 2011
Location: Between Oceans
Posts: 2,641
have you lubricated the hinges? i lube it before major trips or once a year.
mine drops to gear 4 when it's on.
2000 Country Coach Intrigue 40'
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