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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 10-10-2016
Rich Johnson's Avatar
Rich Johnson Rich Johnson is offline
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Default Spring Brake valve

Been looking at an FC air system schematic. Noticed the push pull brake valve located on the dash is connected to a device called a "valve spring brake" which then seems to connect to the rear air relay located over the rear differential. Any idea as to what it does and where it is located?
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  #2  
Old 10-10-2016
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Bill Pape Bill Pape is offline
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Quote:
Originally Posted by Rich Johnson View Post
Been looking at an FC air system schematic. Noticed the push pull brake valve located on the dash is connected to a device called a "valve spring brake" which then seems to connect to the rear air relay located over the rear differential. Any idea as to what it does and where it is located?
its the spring brake, aka park brake, emergency brake, don't take it apart, like the injection pump, it could rip your head or hand off
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1988 FC, Silver Edition
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  #3  
Old 10-11-2016
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Default Relay valve

The dash mounted parking/spring brake valve feeds the pilot of a relay valve that provides air to release the spring brake can. Another input to this relay valve is the rear brake pilot signal-I assume this provides the anti-compounding function to prevent spring brake and air brake being applied at the same time, preventing damage to the s-cam or brake drum from excessive torque on the s-cam. I do not know where this relay valve is located. Note also that the dash valve has an automatic spring brake actuation if the air pressure falls to 30# (I always thought it was 60#).
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  #4  
Old 10-11-2016
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Default Reply to #3

Thanks. I remember reading about the over pressure protection feature. in the spring parking brake/rear service brake. I can see now how the schematic reads. Thanks.
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  #5  
Old 10-11-2016
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Rich Johnson Rich Johnson is offline
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Spring brakes are scary.

My push/pull dash valve leaks. Bought a new one to replace. I think the set point is 40#.

Not sure why the design features a pop valve. Wouldn't it be better for a loss of air event to just to gently actuate the spring brakes rather than a hard landing caused by a valve popping at some set-point? On the other hand, if the air gets to 30-40# it's definitely time to drop the anchor - fast.
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  #6  
Old 10-11-2016
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the relay your talking about is located inside the frame rail under the drivers area,above the axle.
If you want to replace it,you need a skinny young person thats flexable.
When i have replaced them i extend the piping back to an area ahead of the rear axle and i move the relay back there,away from the heat of the engine.

It is not an easy job,i had a skinny employee when i did them.
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2000 LXI 43
Bainbridge,Ga.
Port St Joe Fl.
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  #7  
Old 10-11-2016
Neillynwood@aol.com Neillynwood@aol.com is offline
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quick release valve i think what he talking about but an injecter pump is not that complex finding parts for one is hard
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TALLAPOOSA, Georgia
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Old 10-11-2016
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The valve you are talking about I believe is the SR-1 brake relay valve. A google search for that part number will get a good four or five minute you tube tutorial on what all its job is. I just replaced mine. Extremely difficult!
i wonder if Randy's skinny kid replaced one on a non turbo bus.
I couldn't even see mine till I disconnected the exhaust from the turbo and it's first joint and moved it aside ( couldn't pull it out ) and I sure have never been small enough to get in there. I went through the floor to get it.
I will do a job report with pics soon.
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  #9  
Old 10-12-2016
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If it is leaking, feed it some MMO. When mine leaked I did that and it worked fine after that.
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  #10  
Old 10-12-2016
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yes,the one we did was a turbo 1983FC
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