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Tires, Wheels, Brakes, Steering and Suspensions Discussion of preventative/corrective maintenance and other technical issues regarding your coach's Tires, Wheels, Brakes, Steering and Suspensions and related components.

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  #1  
Old 09-14-2015
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Default FC Parking brake circuit air leak / Brake Relay Valve SR-1

I am on the road. As I started to pull out this morning air pressure was going the wrong way and the spring brake began to drag.
I set the brake, aired up, shut down the engine and released the parking brake.

I could hear a large leak. Seemed to be coming from the frame area at just about the back of the engine.

Of coarse when I moved the bus back up the driveway to be closer to my friends shop in case I wanted shop air, it is no longer leaking.

I see block junction point in about the right place in the frame rail above the left front air bag.

Does any one know if there is a shuttle valve or some such that may not have shifted properly and been venting to atmosphere.

If I am going to tear this thing apart I would rather do it here than beside the road.
Unfortunately I have no idea what to tear apart just yet.
TIA
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Last edited by iamflagman; 12-11-2016 at 07:54 PM.
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Old 09-14-2015
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dump valve is in that area and a PPV

could have stuck?
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Old 09-14-2015
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When my engine was upgraded they changed this valve located on the inside of the drivers side frame rail in that location, I am not sure what type of a valve that it is.

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Old 09-14-2015
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Does the brake air gages hold pressure??
Escaping air sounds from the rear of the engine could be the air dryer,
the main feed line from the compressor, and possibly the governor depending on its location.
The pssst sound can travel and play tricks on your ears , There is also a leveling valve in the center front. Gotta find the leak maybe with a spray soapy water bottle.
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Old 09-14-2015
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John is talking about the parking brake relay valve.
It (if bad) will leak when the parking brake is released,when the parking brake is set,it will not leak.

I was traveling with an FC that had that relay fail,the quick and easy way to get it home was to cage the brake cans on the drive axle,and drive it home (Maine to Fl in this case).
But if you do that,you will not have a parking brake,or the safety of having the parking brake activate if you loose air pressure.
You will need to chock your wheels everytime you stop.

Replacing that valve is a bad job.
I had a pit at the time,and had to hire a local skinny kid to do the work,i was way to big to get in that space.

Fact is,we relocated that valve to a spot way back by the drive axle,extending the air lines to do it.
Now anybody can change it.
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Old 09-14-2015
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I fed my system some MMO (quite a bit) and kept popping the brake valve on and off. I connected a hose where the wet tank drain is and poured MMO into the air hose, then pressurized the system via the hose using shop air, it got that valve unstuck. The MMO gets vaporized by the rapid air flow in the hose so it moves through the system. Been three years I think, and it is still working. I suppose you could put the MMO in the line from the dash brake valve and get it directly to the relay valve.
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  #7  
Old 09-14-2015
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Thanks guys. When I moved the bus back by his shop this morning to get deeper into it the problem resolved and hasn't been back all day.
When I moved the bus this morning to hook up the tow car the system only had about 70 lbs. I had waited for drier to pop before I backed up to his shop, so full system pressure probably made to difference.
I'll get Glacier park reconnoitered with the Samurai and if I have to run home with caged springs I can live with that but I bet I won't have to.
That valve will come out this winter.
Thanks
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Old 09-18-2015
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After two days at Glacier park when we aired up to leave in the morning the problem was back. 4000 ft. at 32 degrees. Tried a couple of taps with a small brass hammer then a hair drier for a while, all no good. Caged the springs and hit the road. Kind of glad I had been through that when I changed out the brake cans. Also nice bright not rusty studs and nuts.
Looks like the relay valve is now at the top of the list.
I am also glad I just installed a King Cruise. I believe the Bendix cruise had an air signal from the parking brake and would not have worked with the parking brake set. King didn't care.

Just to keep it all interesting just a little before Coer d Alene rolling across a bridge joint at speed experienced a total loss of power. Fortunately a nice large shoulder and flat. Jumpered the fuel solenoid to the alternater and it ran. About then the hot wire fell out of the crimp terminal at the solenoid broken from 30 years of vibration. Made up a new wire extension to the solenoid and back on the road, 20 minutes.
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Old 09-18-2015
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Quote:
Originally Posted by Patrick LaBreck View Post
After two days at Glacier park when we aired up to leave in the morning the problem was back. 4000 ft. at 32 degrees. Tried a couple of taps with a small brass hammer then a hair drier for a while, all no good. Caged the springs and hit the road. Kind of glad I had been through that when I changed out the brake cans. Also nice bright not rusty studs and nuts.
Looks like the relay valve is now at the top of the list.
I am also glad I just installed a King Cruise. I believe the Bendix cruise had an air signal from the parking brake and would not have worked with the parking brake set. King didn't care.

Just to keep it all interesting just a little before Coer d Alene rolling across a bridge joint at speed experienced a total loss of power. Fortunately a nice large shoulder and flat. Jumpered the fuel solenoid to the alternater and it ran. About then the hot wire fell out of the crimp terminal at the solenoid broken from 30 years of vibration. Made up a new wire extension to the solenoid and back on the road, 20 minutes.
Your a very brave man driving out there with only front brakes. As far as that goes driving any distance even without the hills.
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Old 09-18-2015
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Rick,
I will have to confirm but I think the actuator for the service brakes can stroke normally with the springs caged. The brakes felt quite normal.
I thought about that and proceeded cautiously, I always depend heavily on the retarder in the mountains rotating between the service brakes and the retarder to keep everything as cool as possible. Nothing seemed different than normal on this trip.
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