brake problems now

bobwoo · November 01, 2015, 10:47:36 AM

I fixed the air leaks and accelerator issues and it built air to 120 so I tried to move her. When I pushed the parking button I heard the air evacuate like normal but the dash idiot light didn't go off. I kept working the button and pushing the brake pedal and rocking her back and forth. She after about 5 minutes moved but it was tight. About the same time air started coming out of the bottom bypass of the brake control and now doesn't stop. I've cut her off and let the air drain down several times but no difference.
I first thought the brake pedal might be froze and not letting the valve close fully so I unhooked the linkage, but no change. Since I'm hearing the air evacuate when depressing the parking button I don't think its that but what else would let the air bypass or could it be in the control valve itself? any thoughts? Bob

Scott & Heather · November 01, 2015, 04:17:50 PM

Maybe your setup is different from mine, but when I apply the parking brake (pull the button) is when I hear the air release, thus allowing the spring brake to apply (air pressure holds it back) and when I release the brake (push the button down) I don't hear air rush out at all. It's quite silent actually. Sounds opposite of what you describe. Just a thought and a free bump

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Oonrahnjay · November 01, 2015, 04:25:42 PM

I wonder if there's a leak between the service-brake and parking/emergency-brake sections (assuming you have "spring brakes"). Often this is caused by a leaking diaphragm in the canister on the wheel. I'm trying to think of a practical way to isolate each canister so you can test this theory. What model bus and what kind of parking brakes?

scanzel · November 01, 2015, 11:25:47 PM

I have a Prevost but when my parking would not release it was because mice had chewed through the air line for the parking brake release button. When I shut the bus off I could hear air escaping somewhere and it turned out to be the air line which runs through a 3" pvc pipe from the front to the back of the bus. The mice got into the pipe and chewed up a 12" section. Second time another line and the bus would would not fill the air bags.

bobwoo · November 02, 2015, 01:16:57 AM

Its a 93 102C3. Spring brakes. If I'm correct when you apply the parking brake, the button sends air to the second stage of the spring brake therefore moving the slack adjuster and locking the brakes. When you release the parking brake the air leaves the cylinder and releases the slack adjuster. I hear the air leaving and I think the dash idiot sensor is under the driver what is making the light stay on, even if the slack adjuster isn't releasing the air pressure has been released so the light should go off?

?. But,,,,, since I am having a high volume of air leaking from the control valve but the two systems aren't directly connected are they? Doesn't the air for the parking come directly from the first stage holding tank and not through the control valve?
My first thought on the valve leak was since it set up so long, crud was interfering with the plunger so it didn't seat proper and that would also count for the brakes still being tight but the parking brake issue has me a bit confused. Is there any connection between the parking valve and main control valve?

luvrbus · November 02, 2015, 01:36:06 AM

I think you have DD-3 brakes with spring brake you hear air escaping when applied and they use air pressure to release the brakes not to apply the parking brake

bobwoo · November 02, 2015, 01:51:49 AM

Yes, sorry DD3 brakes. ok, air engages the brake and air disengages it, that makes sense. Are the sensor or sensors on the spring brake and that is why the light is staying on because the parking brake is not disengaging? If that is correct, I have two separate issues, one parking brake not disengaging two, control valve leak.

??

luvrbus · November 02, 2015, 02:00:05 AM

The light just reads off the push/ pull valve on mine check your brake pedal and be sure it fully released some times they get build up under the pedal and the light stays on and the brakes won't release

bobwoo · November 02, 2015, 05:23:02 AM

Right now I have the entire linkage removed from the control valve/brake pedal. When I depress the parking button the brake light idiot light goes out but the parking brake light remains on so the sensors must be else ware. I can't get under where the spare tire goes because of the release lever is broke, I guess I need to open it up so I can crawl under to get a better look at all of the solenoids and pipe runs to see where everything goes. I have to fix something before I fix what I'm trying to fix, lol

bobwoo · November 02, 2015, 10:49:39 AM

Worked on her all day. Got the bumper open so I could crawl in and get better look. I under air pressure open each of the pipes coming out of the brake valve. No air was present other than the two supplies. I reconnected the pedal linkage and let her build up pressure and kept pumping the brakes and moving the bus back and forth. After about 2 hours the bus started rolling easy but the parking light stayed on. I really hit the brake, I mean really hard, I heard a loud pop right under me so one of the solenoids freed up and the light went out. I moved the bus and it really rolled free.
I turned the parking brake on again and again, it took a real hard kick for it to release and a loud pop from one of the solenoids. I'm alone here so I can't repeat to find which solenoid it is but it might free up?

?(wishful thinking). I figure the control valve is bad and needs to be replaced. I'm guessing that is something NAPA has or can get? Any other place to get?

Scott & Heather · November 02, 2015, 03:14:15 PM

Cool beans! You've solved the riddle it sounds like....wish I were there. I'd help you locate it. Cliff will chime in again and point you in a good direction

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