Air Pressure Drop?

[Alek&Lucia]

No air leaks ?????
Sure, anything else, perhaps Santa Clause ?

[Joe Cannarozzi]

Truk I said some things like darn close to it and that is what I strive for and how it is a lesson in perseverance.

Alek didn't your bus get to be 8 years old before it started showing leaks?

I remember Orren posting that his will hold air indefinitely and they have an old one. I look forward to the day I can do some more with ours.

What is the alternative? The heck with it? This chore is a hard one so lets find something easier?

I know let's polish the rims.

[Jon Wehrenberg]

I have a slightly different explaination than Joe. He can jump all over me if I am wrong.

First....understand my coach, and almost every one owned by POG members has two air gauges, primary and secondary brake. Very few if any have a dash mounted aux air pressure gauge so this discussion is limited exclusively to what can be diagnosed from the driver's seat and in essence is a pre trip brake check.

With parking brake engaged, foot off the service brakes, air system up to max pressure, turn off the engine. The two systems should not lose any pressure. Not in one minute, ten minutes or even overnight because as stated in a previous post there is no pressure on any of the braking system beyond the relay valves. If any pressure loss is detected it should be corrected. 20 PSI in ten minutes of pressure loss is substantial. Steve has it right. A coach should sit for days if not weeks before a loss in pressure is noted.

Now, with the pressure up, engine off and wheels chocked, release the emergency brake. There should be a slight drop in pressure as the spring brakes are released and the pressures should stabilize and stay without dropping. If there is any pressure loss beyond the initial loss the emergency brake diaphragm(s), hoses, or fittings may have a leak and it needs to be repaired. Leaks in the emergency brake release part of the system will grow larger and to the point where you may be shut down.

Assuming the emergency brake release does not show any additional pressure loss, step firmly on the service brakes, and hold the brake pedal. Again, there should be a drop in pressure momentarily, and then the system pressure should stop dropping and hold steady.

If no pressure drop beyond the initial drop is noted after a period of time (a minute or so) alternately apply and release the brakes. When the brake system pressures drop to 40 or 50 PSI the emergency brake knob should spring back to the brake applied position and the emergency brakes should again be engaged.

That completes the brake system checks for leaks and problems.

The aux system is totally independent and the leakdown rate and methods to diagnose leak sources is a topic for another thread, and it is doubtful if anyone has any real definitive answers for that topic.

[Jeff Bayley]

Here's a cut and paste I put on this topic on a prior occasion.

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Related to this topic, I was at Prevost NJ for 3 days solid while they tried to track down why by bags were falling and the coach wouldn't stay level. After replacing one part after the other including the Norgren valves there was still no improvement but I got a lot of "Well, those were bad anyhow and also needed to be replaced". On day 3 or 4, I was letting myself into the coach and I heard a hissing noise. I got the so called mechanics attention to it and after further investigation, it was found that the air operated strut that works the recess floor was leaking air and that strut was defective. This was a converter item and Royal had tied it into a part of the air system that was directly tied into letting the air bags leak out and fall.

For what it's worth to the issue of problem solving and wasting money.

[truk4u]

Good post from Jon about brake air and I think most of the colorful remarks about air leaks (including mine) were directed at the Aux system. If your Aux air never leaks down, please make application to Guinness Book of Records or click your heals together and keep repeating, " there's no place like home, there's no place like home!)

[dreamchasers]

I see the topic of air leaks are close and dear to all Prevost owners. I currently have my coach sitting on the great jack stands that Jon designed and had made. They work great!

On my Country Coach, I had to remove the coach AC condenser to have access (What a pain!). But once it is out of the way, WOW, I can actually reach things. I would advise any Country Coach owners with the Fridgi-Cool AC system, if you are considering any serious work in the area in front of the 'pumpkin', consider removing the condenser coil for better access. Plus, while it is out, I will replace both electric fans on the condenser as preventive maintenance. I am an R12 user, so I purchased a 30 pound keg of R12 from Ebay. I got the idea for the R12 Ebay purchase from Ted Delorme. Thanks Ted.

With the coach safely supported, I am methodically checking all the air circuits. I will advise what I find when complete. I am taking plenty of pictures as I go.

Hector

[Jon Wehrenberg]

Here's a cut and paste I put on this topic on a prior occasion.

---------------------------------------------------------------------

Related to this topic, I was at Prevost NJ for 3 days solid while they tried to track down why by bags were falling and the coach wouldn't stay level. After replacing one part after the other including the Norgren valves there was still no improvement but I got a lot of "Well, those were bad anyhow and also needed to be replaced". On day 3 or 4, I was letting myself into the coach and I heard a hissing noise. I got the so called mechanics attention to it and after further investigation, it was found that the air operated strut that works the recess floor was leaking air and that strut was defective. This was a converter item and Royal had tied it into a part of the air system that was directly tied into letting the air bags leak out and fall.

For what it's worth to the issue of problem solving and wasting money.

Everybody here should give Jeff a huge "attaboy" for what he posted because he has pointed out clearly why as a prevost owner you need to take control of the process of repairing and maintaining your coach.

What Jeff did not post was the costs associated with several days of chasing leaks and replacing a few parts. What he did post was the direction a repair facility will go if you bring a problem to them and not specifiy how you want it addressed.

First, all air bags and all associated Norgren valves will cost less than $2,000 and to replace them all will take no more than 2 days or about 16 man hours of labor. Instead of paying for three days of a mechanic's time to diddle around looking for leaks, bite the bullet and replace all the parts if the system hasn't been repaired or replaced in a long time. It will be cheaper and significantly better in the long run.

Jeff did make a statement that may lead a Prevost owner to draw an incorrect conclusion. Once you have turned off the key on your Prevost (except for some very old coaches) the air in the air bags should be "locked" in the air bags unless the air bags, the Norgren valves or their respective fittings are leaking. The auxiliary air system pressure can go to zero, every device that uses aux air including the step cover air cylinder can be blowing air from it, and the bus should not lean.

And just for purposes of clarity, our suspension system is really not a suspension system to be viewed as a whole, but as three separate suspension systems (front, left rear and right rear) that operate in unison when on the road, or individually when leveling the coach.

[dreamchasers]

At last!!

It was a battle, but the sweet smell of victory is in the air. My brake system's air pressure has been holding for 5 days without dropping a pound. Hooray!!

First, I rebuilt the air dryer for good measure and to assure the supply system was in good order.

Using the bubbler system that I mentioned in Seiverville last year, I was able to find four air leaks in the brake air system. The biggest leak was in the Brake Spring Valve. This device controls the brake air to the front brakes. I replaced it with a new one. I had a very small leak in the 'push to fit' fitting on the back of the secondary air gauge mounted in the dash. The next leak was in a 1/8" union on the tubing going from the aux air cluster (connected to the double shuttle check valve). It was a tiny leak. To my amazement, the air pressure gauge had a very small leak internally. Whew!

Now the brake air system is bubble tight!

brake spring valve 1.jpg
This is the brake spring valve located below the drivers compartment. I was able to access the unit through the front slide out drawer, behind the bumper. It was leaking out of the exhaust (black rubber cover).

brake spring valve.jpg
After removing the spring brake valve, I started removing the fitting and components to be placed on the new assembly

guage back leak.jpg
The push to fit fitting on the back of the dash pressure gauge was leaking. I replaced with a new fitting.

guage.jpg
I am still amazed that I was able to find the small leak in the dash pressure gauge.

bubler.jpg
This is a photo of my homemade bubbler. It monitors all the air going to the components. As you can see, the slightest leak in detected. See the small bubble. I was testing the gauge and this bubble would form over a 45 second period.

[dalej]

Great job Hector! You have done a good job there.

[Orren Zook]

Congratulations on tracking down your leaks Hector and nice job on the step by step photos too!