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International-9.0
Advanced Member
USA
459 Posts |
 Posted - 03/01/2007 : 5:40:22 PM
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I have a 1987 International Conventional S1800 with air brakes. I recently replaced the parking brake air valve and knob with a new one from International. When I push in the knob, it hisses alot out the back and as parking break releases, the hiss slows down, but continues. It will change a little if I rotate the knob or wiggle it, but it doesn't go away. If I hold my hand over the vent in the back, it will re-apply on it's own. I ordered another valve from International and it does the same thing. The old valve is an indentical plastic valve and works just fine (although leaks on occasion, but not like the new ones). I tried pumping down the air pressure and it still does this (in case my system pressure was just a little too high, although I think the safety valve would stop it from getting high enough to leak through the valve seals) Does anybody know why I can't keep it from venting out the back of the valve? And YES, I hooked up the 2 lines correctly.
The way I understand this valve to work is that it has 3 openings. One is a vent in the back, one is hooked to the line going to the spring chambers in the rear brakes, and one is feeding the valve from the main reservoir. When you apply the brake (pull the knob out), the supply is isolated and the spring chamber line is opened to the valve vent which causes a quick drop in air pressure which causes the dump valve in the rear to open and vent all the spring chamber air to the atmosphere. When you release the brake (push the knob in), the valve vent is sealed off and the supply line is connected to the spring chamber line. This charges up the spring chambers to reservoir pressure and releases the rear brakes. i know if the reservoir pressure drops below 20-30 psi (or somewhere in there) that the knob should pop out. I do not know exactly how this feature is controlled. My only guess is that the valve is spring-loaded, but perhaps there is a pneumatic circuit in there somewhere to control this function. Do I have this somewhat right?
Yes I know this is full of fragments and run-on sentences, but does anybody know why I'm having this difficulty? |
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IBTMech
Top Member
USA
973 Posts |
Posted - 03/01/2007 : 6:40:00 PM
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| Hmmmm.... diagnostics from a distance..... you should not have any leaking from the vent port. Your description would suggest a defective valve if you're certain the supply and delivery lines are correctly installed. |
If it doesn't fit, FORCE it.
If it breaks, well, it needed replacing anyway.
Pullin' wrenches for 45 years. |
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Mechan1c
Top Member
USA
853 Posts |
Posted - 03/01/2007 : 6:55:05 PM
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| Does this system use a PP1 to SR1? Are you getting backfeeding air? My buses are plumbed PP1 to SR1 to R14. |
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International-9.0
Advanced Member
USA
459 Posts |
Posted - 03/01/2007 : 7:15:18 PM
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My guess on the first one was a bad seal IBT, but since another brand new one out of the box does the same thing I'm totally baffled. If I hooked the valve up backwards, when the brake was applied, the supply would be going straight out the valve vent, and this does not happen. Plus I marked the supply line with a yellow marking pen before disconnecting it. I don't see how anything could backfeed on the valve unless I don't understand the loop correctly. The only way I could see this occuring was IF
1) The parking brake was applied, not released.
2) The seal between the spring and service chambers was leaking. (this would also cause difficulty in keeping the spring brake released anyways, which I have no trouble with)
3) I then stepped on the service brake, and air would leak through the chambers and back through the valve vent (if the quick release had closed)
My problem is when I have the parking brake released. It will fully release and the bus moves ok, but I"m stumped. I asked one of our mechanics who worked on alot of trucks and he has no idea. I just can't see getting 2 bad valves in a row, although that does happen. I wonder if there is a higher quality valve I can get other than what International has been sending me. I'm tempted to actually take it to a mechanic, but they will just charge me alot and tell me it's a bad valve. I know it's difficult to diagnose from a distance, but thanks for any input.
I am unfamiliar with what you are talking about Mchan1c? What is PP1, SR1, and R14? The valve itself just has "inlet" and "outlet" written on it. If you can give me an idea, maybe I can look at it tomorrow. |
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Mechan1c
Top Member
USA
853 Posts |
Posted - 03/01/2007 : 7:51:26 PM
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PP1 is a "push pull" valve w/the yellow knob (mine are yellow) SR1 is a "Spring release valve" and the R14 is the relay valve back near the rear air cans. A backfeeding SR1 might cause a leak out of a PP1 vent, but it would happen when the PP1 was set, and it sounds like your leak is only when the brake is released if I'm reading this right? Some buses had a push pull valve called a PP-DC although I don't have any of these. The last one I saw was plastic or composite where my PP1's are metal.
Another thought is could there be some sort of miss match with the knob and the valve that could cause a slight exhausting due to the valve being just a hair applied? In other words not completely released?? I'm with you on the head scratching because brake valves are usually very dependable out of the box.
Last questions: Why was the first valve originally changed? Any other work done recently? I love a mystery! |
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IC-RE
Top Member
USA
4117 Posts |
Posted - 03/01/2007 : 9:11:44 PM
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I'm no mechanic at ALL, but I just want to say this... I don't know if it will help at all but here it goes...
On our 99-07 AmTran and IC FEs and REs when you release the parking brake knob, they all hiss for a second and fade instead of like on our other buses where when you release it, it just makes a "fut?" sound, a real quick one. Our newer buses hiss for a second like you are describing. Could it be that it makes this sound because there is a newer valve in place? |
 bus 1980, a 2008 IC RE 300 for Fairfax County Public Schools, Fairfax, Virginia. |
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Kodie
Top Member
United States
2028 Posts |
Posted - 03/02/2007 : 04:50:05 AM
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| While we are on the air brake topic, do BB and IC use a different kind of parking brake? IC parking brakes sound alot different than the BLUE BIRD ones do. When you apply BB brakes the air rushes out faster than IC, do you know what I mean by that? |
Edited by - Kodie on 03/02/2007 2:53:43 PM |
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International-9.0
Advanced Member
USA
459 Posts |
Posted - 03/02/2007 : 4:20:42 PM
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IC-RE, it will continue to hiss without stopping, even if I pump down the pressure or raise it up. The problem is occuring when the spring brakes are released (knob pushed in). It works fine when the brake is applied (knob out).
Mechan1c, are you talking about the sytem that has separate tanks where you can release the spring brake in case you loose air pressure and need to move the bus (to avoid having to manually cage the springs and not be able to reapply them in case the parking brake is needed)?
I don't think mine has any of that and I don't know what an air can is. My only guess is that the air can is the storage for the separate air supply on the above mentioned type of system.
My bus just has the regular spring brake system. I think I'm going to try and get the part from somebody else and try a different brand. I forget to get the brand name off the box for the one I have. Thanks for everybody's help. Let me know if you can come up with anything else.
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mrschoolbus
Senior Member
USA
78 Posts |
Posted - 03/02/2007 : 8:07:56 PM
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Did the original valve do the same thing? Is that why you replaced it. ?
Could be a bad quick release valve or a bad spring chamber. |
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International-9.0
Advanced Member
USA
459 Posts |
Posted - 03/03/2007 : 07:42:53 AM
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The original valve didn't do this near as bad. It was just going a little hard, it would leak sometimes, although alot of that was out the front, not the vent in the back. I could turn it or move it and it would stop most of the time. It was moreso a problem on a cold morning. But I figured since I was getting a knob, I'd get one of those too and go ahead an replace it. I've already had a new treadle valve put in it.
How could a bad quick release or spring chamber cause the valve to leak? Now I could understand it hissing some if the sound was coming from air continuously being sent back to the spring chambers because of a leak, but the sound is coming from the vent as I can put my finger on it and feel it coming out. If I hold my finger on it, the valve will pop back out. Not sure why it does this. |
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International-9.0
Advanced Member
USA
459 Posts |
Posted - 03/09/2007 : 6:08:05 PM
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Update!
I ordered a midland valve (this was the brand of the original valve that was on the bus) and it worked perfectly! Apparently the 2 valves I had were part of a bad batch, the wrong valve, or just plain cheap junk. I'm pretty sure the brand International kept sending me was Excel 2000 or something like that. Anybody else ever have trouble with this brand? |
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Air-Parking Brake valve
