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Tag valve and park brake valve
Just replaced tag valve and parking brake valve , one cracked elbow and both valves leaking , should be good now…..Tom ,Jon or anyone , I did notice that when I repaced the parking brake valve that both the prim , and secondary air gauges went down is that suppose to happen???? New check valves at secondary tank and primary tank….they are good I checked them…….The gauges went down when I took the big line off the bottom of old valve 3/8 line , when I hooked up the line everything works good now… Did not think that, that line could effect both gauges if it had leak in it, just trying to figure it out …. Can that line effect both gauges like that, if it had leak in it???????
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14 Replies
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OK I heard a air leak at the parking brake valve. Since the valve was 20 or more years old I decided to change it. Went and got a new valve and replaced it. Just did a test and still have a air leak. Can’t tell if it is the parking brake or tag axle valve is the culprit. Air built up to 100 psi and would not go any further. Tried to press brake valve down and it would not engage. It just pushed back. Any Thoughts?? Thanks!!
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If I were a betting man I would suggest the leak has nothing to do with the valve and the air leak being heard is likely at the brake chamber and is the first sign a brake chamber diaphragm is starting to fail.
Easiest way to find out is to block the wheels, release the parking brake and go to the rear of the bus to listen.
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Thanks Jon! I will try this and let you know! Appreciate the help!
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Dang, sure miss ole Pete. Talked to him several times over the phone and he always welcomed me up when he wasn’t training. Hope you get your problem fixed.
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If it turns out to be the emergency brake diaphragm I would urge you to cage the emergency brake and cap the air line to the emergency brake side of the chamber. Your service brakes will remain 100% effective but the parking (emergency) brake will be far less capable than they are now. Attempting to drive somewhere to make the repair without caging the brake could be a problem because if the problem is the diaphragm there is no telling how long you will be able to build and hold pressure.
BTW, don’t ask me how I know this.
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A dumb rookie mistake. ok I’m gonna come out and confess, I bought the replacement parking brake valve from Fleetpride not Prevost. They are a little different in design. I’m thinking I may have connected air lines wrong. I have a supply, delivery and exhaust line. My supply line (3/8 yellow line) is correct but after rechecking noticed my delivery line (3/8 Green line) was connected to my exhaust on the valve and exhaust line (1/4 yellow line) is connected to the delivery line. I’m going to correct it and see if that solves the problem. If not I will check the brake chamber but the air leak is right by my seat @ the parking brake valve. Hoping I didn’t damage something by connecting it wrong. I’ll let you know!!
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3/8 yellow line to supply, 3/8 green line to delivery, …. where does the 1/4 inch yellow line go? On the delivery port or exhaust port at the bottom of park brake valve? Or does the exhaust port get plugged because the interlock valve does the exhaust? Questions, Questions, Questions …. If I wasn’t so poor for working on this bus I’d hire a mechanic!
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Here is a Bendix Service Data Manual for their various push/pull type parking brake valves. My bus has a PP-1.
http://www.bendixvrc.com/itemDisplay.asp?documentID=5987
and the only pic and post I could dig up was when I was fixing the leaky TW-1 valve(tag valve).
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Here is a link to the pneumatic diagram. It is the whole coach and you can zoom in on your computer to trace the lines to the valve. This is the old style diagram that was done by a draftsman and scanned.
https://secure5.volvo.com/technicalpublications/pdf/d140162k_e.pdf
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I overlooked manual trans. Both yellow go to del side one on each side of valve. signals air booster for clutch behind dash to operater clutch.. When released….Bottom plug/ check in hole there it might be pressure adjustable. Tried to call but got some music and no ring. Bob PS couldn’t answer question correct because I forgot Manual Trans–Couldn’t see the big picture.
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WOW … Thanks for the help everyone! Today I tried working on park brake valve. No success yet. A truck mechanic told me the 1/4 inch yellow line was the exhaust …. wrong! Robert, I will try putting the yellow on supply and green on delivery. Will use 1/4 inch plug on bottom and let you know how it turns out. I also heard a air leak at the tag axle valve. Guess it will be next to be replaced! Oh and Robert that was Toby Keith singing Trailer hood. “Somethings always going on down in the trailer hood”.
Thanks Don, Robert, Jon & prevost service you guys are the BEST!!!
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Hands on is best. Me especially have a time What I have in my thoughts to someone.
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Don, Thanks for the photo. Can you tell me if your park brake valve has a plug in the bottom? Common sense tells me if it is a exhaust port then it should be open to release pressure. Looks as you have the 1/4 inch yellow line connected to the Delivery port and the 3/8 inch yellow line connected to the supply port. What color is the other Delivery port line? Turns out I have another air leak at tag axle valve on the pressure stat mounted on the side of tag axle valve.
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Sorry Mikie, but I can’t remember. That is the only photo that I have of the PP-1 valve. If I get the time I’ll take that panel off again and take more pics for use.
The color key for air lines is as follows:
Green = Primary
Red = Secondary
Yellow = Parking/Emergency
Blue = Suspension
Black = Aux/Accessories
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