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PT & WB (Twin Axle Pusher Unique Issues) If you have a unique issue with your PT or WB model coach and it can't be answered in one of the other forums here, then this is where you can list it....list your PT Parts here too.

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  #1  
Old 05-03-2018
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Default The Mystery Air Leak (The whole Air system is a mystery to me)

The symptoms pretty much go as follows...
Everything Airs up reasonably well (as long as it's not cold. Then I have a large air leak in the step which I have parts on order to fix.) This is not what I need help with.
In all other cases it airs up well, it takes a little longer than most people but once it's aired up it will start losing air visible first in the front brake system.
The needle at the gauge starts to fall off quite rapidly to the point where I'm down from my normal 110 psi I had at full pressure to 60 PSI within two hours. The rear brake indicator also falls off but at a much slower rate. In the first two hours it probably only went down 10 psi. But it will continue on down a little bit at a time until it hits around 75 PSI and then the suspension will start to go down as well. Usually starting with the front airbags going down faster than the rear. Usually that is sometimes this is not true either other times Front and rear air bags will go down together.
I have used a leak detector and have been all over the bus and repaired many minor leaks. None of those leaks have made a dent in this problem.
As always thank you in Advance for any assistance you can provide.
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Mark & Ginger Lauss
Yuma Arizona
1991 PT 40
Towed 1986 Suzuki Samurai OR 2014 Jeep jk
Location: http://www.bbirdmaps.com/user1.cfm?user=259

Last edited by Bill Pape; 05-04-2018 at 04:27 PM.
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Old 05-03-2018
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Well you're going to have a good time with me on this one.
The title was supposed to be mystery air leak. Not mystery early
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Mark & Ginger Lauss
Yuma Arizona
1991 PT 40
Towed 1986 Suzuki Samurai OR 2014 Jeep jk
Location: http://www.bbirdmaps.com/user1.cfm?user=259
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Old 05-04-2018
ejallison1 ejallison1 is offline
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Sounds like you've looked for leaks and have probably checked it already but aren't the PPV's (pressure protection valves) set at 60 psi. If I read correctly that is where your front brake tank pressures holds-also front airbags down first-maybe front PPV is source of leak.

Understand they have a diaphragm that can leak-also hear tell they are bear to replace. Sounds like your rear does this as well only slower leak-rear airbags stay up longer. Does the auxillary air (wet tank hold pressure-would doubt it if the PPV's were the problem. On my coach there is no air gauge for the wet tank.
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1986 PT 40
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Kansas, Il
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Old 05-04-2018
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I would be looking at the suspension system. Leveling Valves, air lines to the air bags, air bags, dump valves just the whole thing. The PPV valve could be a source or a check valve in the air compressor. Lots of places to look. Since the leak is slow your going to need soap and water in a spray bottle to find it. Take a flashlight, proper safety precautions and wear dirty clothes. Do not crawl under the bus and start messing with the suspension without properly supporting the frame. Don't rely on the leveling jacks to hold the bus up. Use heavy Jack Stands.
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Old 05-04-2018
Clueless Clueless is offline
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There may be other devices to address and fix along the air exit path, but it needs to be leaking out of the system at some point.

I have found air leaking out of my engine compressor suction line when using a shop compressor to air up the bus.

Your brake tanks should not give up air to address a shortage in the auxiliaries.
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96 WB
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  #6  
Old 05-04-2018
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Hi Mark,

I had a similar problem with the front brake air pressure dropping fairly quickly.

I found two things that were causing the problem on my coach.

The main problem was a leaky drain valve on the bottom of the front air brake reservoir. I replaced it with a Bendix 103385 C-1 Drain Cock, 1/4" NPT.

The second problem was a slightly leaky check valve on the supply line where air enters the front air brake reservoir. I replaced it with a Haldex KN23000.

The front air brake reservoir is a little difficult to see or get to, it's up front behind the generator.

NOTE: The drain valve on the rear brake reservoir and on the wet tank reservoir were also leaky so I replaced those as well and as a preventive measure, I replaced the one on the Aux air tank that wasn't yet leaking.

Since 3 out of 4 of mine were bad, I suspect that there are a lot more out there that are leaking.

As Rick said, there are "Lots of places to look" and "Do not crawl under the bus and start messing with the suspension without properly supporting the frame. Don't rely on the leveling jacks to hold the bus up. Use heavy Jack Stands".
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John Wyatt
Titusville, Florida
1991 40' WLWB-WTB
Body Number F095567
My Location: http://www.bbirdmaps.com/user1.cfm?user=4

1991 40' WB ...From 2008 - Present
1984 ½ PT-36 .From 2000 - 2008
1973 FC-31 .....From 1991 - 2001
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Old 05-04-2018
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Quote:
Originally Posted by ejallison1 View Post
Sounds like you've looked for leaks and have probably checked it already but aren't the PPV's (pressure protection valves) set at 60 psi. If I read correctly that is where your front brake tank pressures holds-also front airbags down first-maybe front PPV is source of leak.

Understand they have a diaphragm that can leak-also hear tell they are bear to replace. Sounds like your rear does this as well only slower leak-rear airbags stay up longer. Does the auxillary air (wet tank hold pressure-would doubt it if the PPV's were the problem. On my coach there is no air gauge for the wet tank.
I have a pressure gauge on The airline going to my black tank and (I'm assuming someone correct me) that this one runs off of the auxiliary tank. All indications are that Air tank that feeds my pneumatic dump valves runs Low on air first. I have repaired a couple of air leaks in that area but there has been no appreciable improvement.

For the most part the PPV seem to be doing their job but it really does fight to get past that 60 PSI Point when pressuring up and it does take longer for the air to go down once it hits the 60 PSI point on the way down.
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Mark & Ginger Lauss
Yuma Arizona
1991 PT 40
Towed 1986 Suzuki Samurai OR 2014 Jeep jk
Location: http://www.bbirdmaps.com/user1.cfm?user=259
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  #8  
Old 05-04-2018
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MarkYuma MarkYuma is offline
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Quote:
Originally Posted by Rick View Post
I would be looking at the suspension system. Leveling Valves, air lines to the air bags, air bags, dump valves just the whole thing. The PPV valve could be a source or a check valve in the air compressor. Lots of places to look. Since the leak is slow your going to need soap and water in a spray bottle to find it. Take a flashlight, proper safety precautions and wear dirty clothes. Do not crawl under the bus and start messing with the suspension without properly supporting the frame. Don't rely on the leveling jacks to hold the bus up. Use heavy Jack Stands.
I have played with suspension in this project a little bit already. And anytime I work on suspension I want to have my wheels on blocks and use jackstands and hydraulic jacks as back up. Part of my problem is I can't seem to keep air to stay in the system long enough for me to find out where leaking out from.
One thing I have not gone yet is put my ex ternal compressor on the shop air valve stem The back of the bus. Which tank does that feed into?
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Mark & Ginger Lauss
Yuma Arizona
1991 PT 40
Towed 1986 Suzuki Samurai OR 2014 Jeep jk
Location: http://www.bbirdmaps.com/user1.cfm?user=259
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  #9  
Old 05-04-2018
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MarkYuma MarkYuma is offline
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Quote:
Originally Posted by Dieselbird01 View Post
Hi Mark,

I had a similar problem with the front brake air pressure dropping fairly quickly.

I found two things that were causing the problem on my coach.

The main problem was a leaky drain valve on the bottom of the front air brake reservoir. I replaced it with a Bendix 103385 C-1 Drain Cock, 1/4" NPT.

The second problem was a slightly leaky check valve on the supply line where air enters the front air brake reservoir. I replaced it with a Haldex KN23000.

The front air brake reservoir is a little difficult to see or get to, it's up front behind the generator.

NOTE: The drain valve on the rear brake reservoir and on the wet tank reservoir were also leaky so I replaced those as well and as a preventive measure, I replaced the one on the Aux air tank that wasn't yet leaking.

Since 3 out of 4 of mine were bad, I suspect that there are a lot more out there that are leaking.

As Rick said, there are "Lots of places to look" and "Do not crawl under the bus and start messing with the suspension without properly supporting the frame. Don't rely on the leveling jacks to hold the bus up. Use heavy Jack Stands".
John. I spent some time looking at the pneumatic schematic diagram just an hour or so ago and the points You are making are exactly what I thought about. There has to be something close to one of the tanks either the auxiliary with a really bad leak or the front air tank with equally as bad of a leak. I know I go around and pretend I'm dumping water out of all my air tanks ( I don't think I've ever gotten any water out of any of them) but I'm not really sure which is the auxiliary tank :-|
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Mark & Ginger Lauss
Yuma Arizona
1991 PT 40
Towed 1986 Suzuki Samurai OR 2014 Jeep jk
Location: http://www.bbirdmaps.com/user1.cfm?user=259
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  #10  
Old 05-04-2018
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Quote:
Originally Posted by MarkYuma View Post
John. I spent some time looking at the pneumatic schematic diagram just an hour or so ago and the points You are making are exactly what I thought about. There has to be something close to one of the tanks either the auxiliary with a really bad leak or the front air tank with equally as bad of a leak. I know I go around and pretend I'm dumping water out of all my air tanks ( I don't think I've ever gotten any water out of any of them) but I'm not really sure which is the auxiliary tank :-|
Hi Mark,

The Aux air is actually stored in two tanks - the wet tank and the Aux wet tank.

See attachment:
Attached Files
File Type: pdf Dual Air Brake Assy. 3907 WLWB.pdf (893.8 KB, 80 views)
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John Wyatt
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1991 40' WLWB-WTB
Body Number F095567
My Location: http://www.bbirdmaps.com/user1.cfm?user=4

1991 40' WB ...From 2008 - Present
1984 ½ PT-36 .From 2000 - 2008
1973 FC-31 .....From 1991 - 2001
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