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DougBarr32

'05 Tiffin Air Pressure Bleeding Off

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Looking for some help please. '05 Tiffin bus.

When the air system is fully inflated engine running the the pressure cycles constantly from 125 to 95 and back and forth driving down the road with no brake action taking place.

Any thoughts. 

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Doug,

Sounds like you have a significant air leak or problem with the air system governor.

When you shut off the engine, how long does it take for pressure to drop?

While pressure SHOULD cycle, it should be over a period of many minutes-- even longer if not using brakes and on smooth road.

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Yes it takes about 6-7 minutes for the pressure to drop and the compressor to come on. I tested this sitting in the driveway ebrake off wheels choked no brake applied. Both frt and rear brake gauges drop at the same rate.

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What happens when you shut off the engine with air pressure at cut-out PSI around 125 PSI?  How fast does it drop?

With engine off, can you HEAR a leak as you walk around the coach?

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Sorry for the delayed response. I will air up and allow the the purge valve to blow off, turn off the engine, then time the pressure drop to 95psi and also look and listen for the leak. 

 I will get back with you as soon as I can. 

Thank you for your help. 

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If you have the ability to get under the coach safely......air bags deflating makes getting under a coach VERY dangerous unless you have a pit, a lift or a way to raise and insert proper jack stands....... you will likely find a leak quickly.  On my coach when the air pressure was dropping while driving the tech found that one of the air brake lines had been rubbing and was no leaking.  Very bad.  A new hose and we were back in business.  Assuming your coach rides on air bags you may also be able to watch what happens after hours with the coach turned off.  If the coach drops in height or tilts to one side of the other it's more likely that you have a leak at the air bag connection, the air bag itself or one of the connections leading to the valves that inflate the air bags.

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I have done some more testing on this issue the coach is making a fluttering sound or you could call it light honking sound coming from the underside in where the air tanks are located when the system is fully pressurized. Also I pressurized the system and let it sit for three days when I turned the coach back on the front air gauges read 60psi and the rear air guage reads 95psi. Very interesting because they both seam to drop or  loose air psi at the same rate of loss.  

So i charged up the air let it blow off then turned off the engine and watched the gauges. both gauges went down at the same rate over 12-15 min it was at about 105 psi-- both front and rear. 

Any thoughts on this continuing issue would be appreciated. I have ordered new tank pull drain valves and also a complete air dryer assembly to replace the old one. I do not know the last time it was serviced so I think it  best to replace the complete unit . Haldex da 34160 

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Sounds line you are on the right track.

And, to save some $$, I have no problem with a FACTORY reman dryer (Factory being Haldex, not Bubba using "almost as good" overseas parts).

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It took me a month or so but I have what looks like to be my leak. I replaced my Haldex air dryer and replaced my tank pull air drain fittings. I sprayed down the complete air tank area and found some connections with small leaks so I took care of them while I was there. With no apparent big leak I was frustrated. 

In looking at the tank design and watching both gauges continuing to lose air at the same rate I went back to the drawing board. It has to be a tank circuit that joins both tanks together. So with all that said on the 05 Tiffin Bus there is a customer air manifold mounted in the left front lower electrical compartment. It supplies air to the inside air powered step cover. The Mac valve is leaking air out the exhaust port constantly. I have heard the Mac valve could not be sealing the exhaust port or the air piston in the step cover could have worn seals in it witch can cause the exhaust port to leak as well. Any help to resolve this issue would be appreciated. 

Thank you.

 

Doug,

 

 

 

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Joe, I isolated the mac valve from the air step cylinder ( the mac valve does not leak on its own)  the cylinder will need rebuild it or replaced.

Air Leak, At this point on the the front tank pressure goes up and down as the engine is running in my driveway and while driving 120psi-95psi.( about every 5 min) The odd part is I have soap sprayed down the tank system in the front,the valving,the front air bags, and the front leveling valve. The leveling valve is seeping just a little bit at the connection over time. 

So my finding is when engine is running the front air is cycling so I am asking for help with this: What in the air system is turned on or opens up when the engine is running

If I can determine this I should be able to find and correct the source of my cycling issue. 

If anyone has any help they can offer I would appreciate it.

Thank you,  05 Tiffin bus XC chassis

 

 

 

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Doug,

I would call Freightliner with your VIN and ask for a copy of your air system schematics. Also, give Tiffin a call to find out how they modified/added to the air system (things like air horns, air powered step covers, etc).

Have you listened for the air dryer purging (in driveway with engine running)? How frequently?

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Thank you for your response. 

I do have a schematic from freightliner of the air system. It has color coded air lines listed as well. I have sprayed down the lines going up to the front of the coach with no luck. And no air noise.

Good idea on the Tiffin chassis additions. Maybe they have a schematic on there part of the air system. 

The air dryer purges every 5 min. With the front tank psi going up and down. 

Any Additional thoughts.

 

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1 hour ago, DougBarr32 said:

My mental road block is loosing 25 psi in 5 min when running out of the front tank. When parked it does not loose all of the air in 15min. After a few days it goes down to about 65psi. ?

 

There is a 65PSI. PPV-(Preset Pressure Valve) in the line between the tank and the point you mentioned. So it sounds like you have a failed Connector or leak in the line from a pressure manifold in the line supplying air to the point mentioned or to some other point from the same manifold. 

Rich.

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Doug, got your drawing in hand. The exact same basic drawing is for our coach.

Think you will find the leak after the PPV of the Secondary air supply. If it was before the valve the air pressure would drop below 65lbs. when setting. 

With the drawing rotated 90deg. to the left,. Bottom left hand corner. Grid A to D vertically and 8 to 1 Horizontally.

Find the Customer Manifold near the grid intersection of #6 and B. That line runs back to the 65lbs. preset pressure valve connected to the Secondary air supply tank at the junction line of #5 an 4 and near the top of B. Do you see the manifold in question? This is the valve that is limiting the air loose at 65lbs. NOTE ! there is often a convince air outlet located somewhere on the coach. They are often located out in the elements and they stick open. Oil up the connection and find a male connector that matches. plug into and release the plug several times to see it the OEM socket will seal up !!! if that is the point of the leak.

The customer Manifold supplies air to the air horn valve and the engine Pack Brake. Joe thinks your Coach has an engine compression set up and in that case you do not have that air line. The High / Low switch's if your equipped with this system is controlled by 2 relays and electric valves in the valve train of the engine and oil pressure is used to control the valve location of the exhaust and intake valves. 

The other air lines split of from the same PPV supplies air to the air ride system and Joe thinks you have the auto air down system connected to your leveling system and not a manual dump switch located at the drivers station. 

If I have you totally confused, do not feel bad. Everyone that owns a DP goes through a mind altering experience for a time and there is always something new popping up.

I admirer you for stepping out of your comfort zone to understand how these systems work. It will pay big dividends down the road ! You will know when something is not quit right and have an idea of where to look. 

Note! Got a PM from Joe and he has been working on over the road trucks, an your issue is got him baffled! Maybe a good cup of coffee or something to help clear his mind.

Rich.  

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A wild guess-- I have a 2007 Freightliner chassis and I developed an air leak that I did not catch for a little while.

The air pressure gauge was the problem it had cracked and was leaking air.

Fix new air pressure gauge.

 

JimR

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