BCM Community
Bus Discussion => Bus Topics ( click here for quick start! ) => Topic started by: rcbeam on August 30, 2011, 02:26:29 PM
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Decided it was time to investigate some air leaks today, so got out the soap squirt bottle and crawled into the spare tire compartment. Found a couple of fittings that just needed tweaking but the big item was a square silver thing that had the marking of QR1 on it. My pressure regulator for the blower belt tensioner has been leaking out the weep hole for a while, but when I sprayed it down, I had a whole nest of bubble all over it. So it was leaking much worse than I thought. Also found the air control for the missing shutters leaking lots of places so I am just going to remove and cap the air line for that. Called our good busnut friend Luke and he said the silver thing was a quick release valve (guess the QR1 was a big hint for him). He is sending me rebuild kits for both the pressure regulator and the quick release valve.
I also looked at the tires on the rear. I could not find the DOT date on the drives but I found it on one tag... was 3301. Had no idea the tire was this old. The drives look really good and I cannot find any cracks any place but can't find the date either. Not sure if they put it one both sides or not. I've not really had the bus on the road much since I've had it, but guess it's a good thing. I put new steers on last fall but looks like I need 6 tires for the rear now. Guess that will take care of the best part of 3 grand. My two fronts installed were just change under $1k for the pair.
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I believe the dot codes are only on one side of the tire.
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Both the quick release valve and the pressure regulator are easy rebuilds, you do need to reset the pressure regulator to 21 PSI for the blower fan belt. One thing - the exact same pressure regulator is used for the emergency/parking brake system. Mine failed on me, so now I carry a spare unit set to 85 PSI so I can swap it if I need to.
Brian
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Received the kits from Luke Friday and proceeded to rebuild the parking brake QR1 first. PROBLEM 1: Only two parts in the kit, diaphragm and grommet (o-ring). When I read the OPERATION portion in the manual page 4-19, it says in part "...the diaphragm spring forces the outer edges of the diaphragm against the body seat." in paragraph 2. I could not find a 'diaphragm spring' in my QR1. When I reassembled and installed the valve, aired up the bus I STILL have air leaking out of the exhaust port when the parking brake is SET, but not when released. Same condition I had before I rebuilt the valve. The diaphragm was hard in the center and so it still needed to be rebuilt, but now I have no clue why it still leaks. Could I have a leaking parking brake chamber feeding back through or something wrong some place else causing the leaking out the exhaust port or am I missing a diaphragm spring?
PROBLEM 2: I also rebuilt the pressure regulator for the blower belt tensioner. It leaked out the weep hole in the back of the regulator and when I sprayed it with soap bubbles, it blew bubbles from everywhere really bad. After the rebuild I have just a few very small bubbles around a couple of screws and I snugged them down good but I have LOTS of air out the weep hole... so much that I could hear it leaking all the way from the front of the bus. It is leaking much worse out the weep hole now than it did before I rebuilt it. So I shut it all down, closed up shop and came home. On the drive home I thought about the fact that I had not yet adjusted the air pressure to 21 lbs... I did install the adjusting screw the same number of turns as before, but have not checked the pressure. I was told by a bus mechanic friend of mine that the leaking out of the weep hole is due to a leaking air cylinder but when I asked Luke about it when I ordered my kits, he said he had never heard of that.
So any ideas on what I should check or do next to address the two leaking rebuilt valves?
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I had the same leak off my alternator tensioner. I pulled the cylinder apart went to the hardware store got new orings all is good. cylinders are spring loaded I held it in the drill press took the end off and release the tension. if I remember correctly it only had about two inches of preload
Rick
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Thx Rick...looks like my friend was right and I need to put new o-rings in the air cylinder.
Back to the parking brake QR1, I have been studying the book and looking at air diagrams. Looks like the QR1 output goes to the inversion valve. I have read the section on the inversion valve operation, but can't quite get my brain wrapped around it all. So I still don't know if I need to rebuild the inversion valve, or if I have a problem in on of the rear brake cans, leaking back through the inversion valve to the QR1.
Anybody care to offer an input?
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I would think you could take the airline off the brake can and plug it see what happens. That's probly where I would start
Rick 74 MC-8
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post your unit number so I can use the correct schematic to spin you some more!
happy coaching!
buswarrior
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buswarrior: DOM: MAY 1976; SERIAL NO: 1507; UNIT NO: T46-442. I have a TMC COACH. My book is MCI and the last time I called MCI to order some parts I asked them about TMC books or converting my serial number to a MCI number to reference the schematics in the MCI book.... he had no clue.
Hope this helps you find something... thx for looking for me.
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I just got back in from trying to adjust the pressure on the blower belt tensioner pressure regulator. When I hooked up my guage, it ready 35 psi, so I backed out the bolt on the back... the lowest it would go is 26 psi with the bolt almost ready to fall out. When I screwed it in, the pressure went up but the leaking out the weep hole slowed down. At any rate, it won't adjust down further than 26 psi.
It looks like to me the regulator is backwards. The control valve is plumbed to the outlet side of the regulator with the inlet side going to the test port and the rear most hose on the air cylinder. Maybe I just don't understand it.
I'm lost.
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The pneumatic belt tensioner is powered in both directions.
It will provide belt tension one way, and will retract the tensioner in order to make belt changes a snap.
If it is working correctly...
I'll get the manuals out for the rest if I can squeeze in a little time. Awful busy with work, too tired for schematic chasing and typing stuff accurately that needs thinking!
happy coaching!
buswarrior
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I just redid mine this morning, because when I re-installed mine I after changing the engine I couldn't get it to work right, symptoms exactly the same as yours. Air dumping out of the exhaust hole on the pressure limiting valve, the control valve wasn't working right. I took it all apart and installed a new pressure limiter, and plumbed it so that air comes into the control valve, into the input side of the pressure limiting valve, and out to the rear port of the cylinder. I set the limiter to 21 PSI. As it came out of the bag it was set to zero, and I cranked it in a few turns to get it up to 21 PSI, so they definitely should be able to got that low.
Now it works fine, the air cylinder is leaking a bit as is the control valve, so I will take them apart and have a good look.
Edit: took apart the control valve and replaced the O-rings. It's held together by a snap ring on the bottom, fiddle that off and it comes apart. Now the last problem seems to be that the cylinder is leaking air from the rear section to the front section, it travels out of the hose and back to the control valve and out the exhaust port at the top, and it probably shouldn't do that. I will take it apart later.
Brian
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So Brian, according to your plumbing description, my pressure regulator is indeed installed backwards and has been all along. Probably why I can't get it to adjust down correctly.
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Well maybe it was a funky option because mine was installed exactly the same as yours, so who knows. My pressure regulator is now brand new, from Luke, but it adjusted down to zero. I adjust mine off the bus, in my shop, I just screw in a gauge on the outlet side and an air line fitting on the inlet side. I did find a picture of it in my manual that shows that it is supposed to be installed with the air going into the inlet on the pressure regulator and out the outlet (it seems so silly to write that, but there you go).
I am at the point where I need to rebuild the air cylinder and then it should be good. I am leaking from the push side of the air-cylinder out the retract side port, so that is the last thing I need to fix. I put new o-rings in the control valve, but it wasn't the problem.
Brian
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I asked Luke about my pressure regulator and QR1 valve issues and he was supposed to call me back. Haven't heard from him yet. As for the book mentioning diaphragm seat and spring, I poked around on the internet and found a site that showed the evidently older QRV valve as having the seat and spring, while the newer QR1 does not have a seat and spring. So mine is not supposed to have one. There u go. As for leaking out the exhaust port it still does. Tomorrow I am going to take it out and apart again and turn the new diaphragm over and reassemble it and see what it does. I am also going to study the book more and see if I can figure out what would probably be leaking out the exhaust port. Someone mentioned the brake cans leaking, but when I looked at the book the inversion valve is the first thing inline from the QR1 so I don't know if it could be bad or not either.
As for the pressure regulator on the blower belt tensioner, mine was installed backwards originally... not sure how dumb you need to be to do that, but it was. So today i removed it, took it apart just to check things inside again, put it back together and installed it with the control valve to the IN and the OUT to the air cylinder. Now it works like it should, I was able to adjust to 21 PSI (it had a metal tag on the adjustment stating the pressure required) and best of all it now does not leak out the weep hole or any place else.
So one down and one still to go. Maybe if I study the book part on brakes enough I'll figure something out on the QR1 leak.
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The whole point of the QR1 is to exhaust air coming from the brake can if there is no delivery pressure to hold it closed so that the brakes release quickly after application. Hence the advice to look for something wrong downsteam of the QR1 sending air back to it.
Good news on the pressure regulator, I have yet to rebuild my air cylinder but hopefully it won't be too much of an issue.
Brian
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Brian: Now that makes sense... finally one of the light bulbs in my brain just came on. DUH... now I feel dumb. So since air is leaking out the parking QR1 then the problem is probably the parking diaphragm in on of the rear cans. If you're going to open on up should just change it all out and I did read in the book if you rebuild one then you should do the other on the same axle.
Is rebuilding one of these rocket science? Anything I should know of be scared of? Is the spring inside under a lot of pressure?
thx guys for your help. Especially you, Brian.
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Lets review DD3 101 tomorrow. Too much scallopini and red wine tonight...
Brian
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Here is my take on what might be happening. I think I have the logic right, but like I always say air brake systems are bloody complicated! I could well have this totally wrong, if so I hope someone points that out! :o
The QR1 in the emergency brake circuit is designed to allow the air pressure in the emergency/parking brake chamber to release quickly when the brake is released. Air flows through the QR to the inversion valve (via an 85 PSI pressure regulator, the same model as your buddy the pressure regulator on the belt tensioner, hence I carry a spare). The inversion valve normally supplies air to the locking section (front air hose) on the DD3 and keeps air away from the parking brake section. That keeps the shaft lock open, and lets the service chamber work. When the parking brake is applied, the inversion valve switches, and sends air to the parking brake section (the rear port on the DD3) and takes air away from the locking section so it can lock the pushrod shaft in the extended position.
the only time you are supposed to get air exhausting from the QR1 is when the parking brake has just been released - air rushes out and lets the parking brake off. If you are getting air at the exhaust of the QR1 when the parking brake has just been applied, then the QR1 is leaking pressure that it is supposed to be sending down to the inversion valve. If you are getting air when the parking brake is off but the service brakes are applied, then air is leaking at the DD3 into the parking brake chamber from the service brake chamber. Suspect a leak in the parking brake diaphragm on one of the DD3's. If you are getting air exhausting at the QR1 when the parking brake is off and the service brakes are not applied, suspect the inversion valve - the only thing that has air pressure at that point is the locking port on the DD3, to keep the push-rod shaft lock disengaged - and it's not all that likely that air is going to leak past the locking section seal, into the main service chamber and then into the parking brake chamber to get to the QR1.
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Brian: I have looked at the diagrams and read the descriptions until I am dizzy. My brain hurts. I have read your explanation and it pretty much makes sense to me and I can follow it along with the diagrams. The last time I aired it up, if the parking brake was ON, I had air leaking out of the QR1 at a steady rate. If I released the parking brakes and they were OFF, then I had no leaking after everything settled. I could not try the service brake.
I am going to air it up again Saturday and give all this another look and take specific notes. Then I'll post back. By opinion right now is that I have a parking brake diaphragm leaking and possibly a troublesome inversion valve. It seems to be to be best to rebuild the inversion valve and the two rear brake cans and be done with it. The diaphragms in the QR1 and pressure regulator were both hard and in bad shape, so I figure most of the other brake rubber parts are probably bad too.
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I removed the parking brake QR1 valve again, and turned the diaphragm over and reinstalled it. The QR1 still leaks a 'LITTLE' air when the parking brake is applied, but none when released. Now I have since discovered that my push-pull valve is leaking out the bottom where the nut is when the PB is applied. I called Luke today to order a new push-pull valve and was able to talk to one of the guys there about my leaking QR1 and he suggested that it is caused by the leaking push-pull valve. He said replace that and then see what you have... so I ordered one from Luke. We'll see hopefully by this weekend.