Air loss-only when driving

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Air loss-only when driving

July 06, 2014, 06:16:07 pm

So the fun begins. At highway speed, I am losing air at a quick rate. Both tanks go from 125 to 90 and back about every 90 seconds. Trick is there is no air loss while stationary, not even with wheels chocked and brake released.

FOT advises it is okay to drive to next stop (4 hours) and will arrange service tomorrow. Seems like a lot to ask of my compressor.

Thoughts or suggestions?

Re: Air loss-only when driving

Reply #1 – July 06, 2014, 06:52:17 pm

Could be an airbag leak while in motion and the coach in a little different attitude.

Pierce

Re: Air loss-only when driving

Reply #2 – July 06, 2014, 07:24:24 pm

Quote from: Lucky1 – July 06, 2014, 06:16:07 pm

So the fun begins. At highway speed, I am losing air at a quick rate. Both tanks go from 125 to 90 and back about every 90 seconds.

Thoughts or suggestions?

What sorts of roads (expansion joints/bumps/curves) are you driving on? With air suspension there will be some exhaust of the air bags that will cause need to reinflate. 90 seconds seems a little short of an interval, but it's not unheard of if the suspension is having to respond frequently.

We were also surprised to find both our tag air bags were leaking (one pretty significantly) this year. Not obvious until it was soaped. The tag bags are a different mfr and p/n than the other 8.

Re: Air loss-only when driving

Reply #3 – July 06, 2014, 07:34:46 pm

Could it be the mechanical gauges. One of my gauges is erratic with no obvious sign of air pressure loss. Quick correction. Not sure if yours are mechanical.

Good luck.
David

Re: Air loss-only when driving

Reply #4 – July 06, 2014, 07:38:18 pm

Is this a sudden problem? What has changed, what maintenance has been done? Of course 90 psi to 125 psi means the compressor is working correctly, but too often.

Our coach does the same as yours, only it takes many more minutes and it is mainly just the rear brake tank, which on our coach feeds the rear air bags, and gets more often on bouncy pavement. As we move down the road, the rear air tank goes down as rear ride height releases and refills rear bags.

Ride height valves could be a problem, but I am at a loss why both front and rear would go down, and to 90 in a minute and half. If you had the problem with front or rear, I would say a ride height valve could be leaking. Ride height valve is taken out of the circuit when ignition is off, so a bad ride height valve would not show up when parked.

Re: Air loss-only when driving

Reply #5 – July 06, 2014, 07:47:52 pm

Cycle time is still around 1:40 for both tanks and both gauges. Did stop at Love's, built up air and turned off engine. Crawled under front and rear of coach and heard no sounds of leak. Gauges reflect no material loss of air. Interstate terrain has varied from smooth to rough. Cycle time is similar throughout all road conditions. Pressing on to Cincinnati. If any good mechanics are known in the area, suggestions appreciated.

Thanks! Karen (for Joe)

Re: Air loss-only when driving

Reply #6 – July 06, 2014, 07:53:16 pm

I'm sure that your newer models still have the wet tank valve behind the driver side rear tires, this could be opened slightly and you wouldn't be able to hear it over the sound of the engine. I'd start by checking this.

Re: Air loss-only when driving

Reply #7 – July 06, 2014, 08:17:37 pm

Air Governor could be causing cycling while driving. Other than replacing it all I can think to do is diddle with adjustment. If you are in a truck stop there is most likely a mechanic nearby or a parts house.

Gary B

Re: Air loss-only when driving

Reply #8 – July 06, 2014, 09:05:19 pm

Does it leak when the key is on but the engine is NOT running? One thing to check is the air drier.

But, the tanks should both have check valves on them so that air shouldn't leak backwards.

You'd have to check your schematics, but it would appear the only common "out" point from both front and rear would be your brake pedal.

I'd have to double check to see if the parking brake release comes just from the rear tank.

Re: Air loss-only when driving

Reply #9 – July 06, 2014, 09:14:06 pm

If it does not leak when parking brake is applied, would be looking at the parking brake canisters, blown pancake ? They use air to hold the parking brakes off so you can drive it.
If that is the case, would not be driving it as that wheel will be draging the parking brake, sure will get HOT & most likely destroy pads & rotor ?
Be nice to have a better description of what is.

Re: Air loss-only when driving

Reply #10 – July 06, 2014, 09:17:24 pm

Quote from: Gary Bouland – July 06, 2014, 08:17:37 pm

Air Governor could be causing cycling while driving. Other than replacing it all I can think to do is diddle with adjustment. If you are in a truck stop there is most likely a mechanic nearby or a parts house.

Gary B

The air governor sounds like a very likely culprit. We will look at it in the morning and report back. Thank you for all the support.

Re: Air loss-only when driving

Reply #11 – July 06, 2014, 09:20:58 pm

Quote from: Dave M – July 06, 2014, 09:14:06 pm

If it does not leak when parking brake is applied, would be looking at the parking brake canisters, blown pancake ? They use air to hold the parking brakes off so you can drive it.
If that is the case, would not be driving it as that wheel will be draging the parking brake, sure will get HOT & most likely destroy pads & rotor ?
Be nice to have a better description of what is.

Thanks Dave. The wheels were chocked, parking brake disengaged, engine running AND off. There was no leak in either situation.

Air leaking when moving

Reply #12 – July 06, 2014, 09:32:45 pm

Lets see, you released the parking brakes, engine running, in neutral, air pressure steady, no leaks. BUT when you put in gear and start moving it LEAKS big time ?
Do I have that right ?

Re: Air leaking when moving

Reply #13 – July 06, 2014, 09:44:20 pm

Quote from: Dave M – July 06, 2014, 09:32:45 pm

Lets see, you released the parking brakes, engine running, in neutral, air pressure steady, no leaks. BUT when you put in gear and start moving it LEAKS big time ?
Do I have that right ?

Yes! You got it.

Re: Air loss-only when driving

Reply #14 – July 06, 2014, 09:52:27 pm

Well that is a mystrey indeed, appears as soon as you engage the D on transmission the leak starts. Not familiar with the Allison air needs, otherwise all sounds normal.
Over my head for sure, I would have bet it was the parking canaster pancakes when released brakes

SORRY TO BE CLUELESS.
Dave M

Re: Air loss-only when driving

Reply #15 – July 06, 2014, 10:02:04 pm

If it was me under this situation, I would get the rig over a pit and soap the dickens out of all rubber air lines and valves that vent to atmosphere. No mysteries, it's going some where. It may not be audible under the conditions you had it in, so maybe it's going into a canister somehow and then to atmosphere. A good soaping should find it. Have a great day ---- Fritz

Re: Air loss-only when driving

Reply #16 – July 06, 2014, 10:06:40 pm

Quote from: fkjohns6083 – July 06, 2014, 10:02:04 pm

If it was me under this situation, I would get the rig over a pit and soap the dickens out of all rubber air lines and valves that vent to atmosphere. No mysteries, it's going some where. It may not be audible under the conditions you had it in, so maybe it's going into a canister somehow and then to atmosphere. A good soaping should find it. Have a great day ---- Fritz

Totally agree with you Fritz. We plan to soap it all tomorrow. Thanks to everyone for the advice. Should we meet up at next event...beverages on me.

Re: Air loss-only when driving

Reply #17 – July 06, 2014, 10:14:06 pm

There's also an air control valve on the transmission retarder. Several of us with 2003's have had to replace it. In our case, though, it was a pretty audible leak and present even when in "N" with the parking brake set. Dick S. has some very useful photos

Replacing transmission retarder valve (split from What did you do to your coach)

Re: Air loss-only when driving

Reply #18 – July 06, 2014, 10:33:40 pm

I had to replace mine too Michelle.

Re: Air loss-only when driving

Reply #19 – July 06, 2014, 10:38:34 pm

I replaced that valve on the 240 I had and got it on amazon for $125 just a short time ago. Was not leaking but at that price I did it. I have the old as a spare.
JohnH

Re: Air loss-only when driving

Reply #20 – July 06, 2014, 11:23:23 pm

Joe here (Karen typed while I drove. Thank you baby.) To make it even more interesting, coming into town, pressure appears to hold below 30 or so. So, tomorrow Karen gets the soapy water task while driving down the highway. :0) Man I over married. When you meet her, you will understand the lucky thing.

No hot brakes upon arrival.

Transmission retarder... Good tip too.

A sincere southern thank y'all! Will let you know how it turns out for future reference.

Re: Air leaking when moving

Reply #21 – July 07, 2014, 12:26:42 am

Maybe you diagnosed it: When you release the parking brake, air pressure is put to the outer brake can to compress the parking brake springs. Just no fun getting under coach with engine running and parking brake off.

You may find that if you have full air pressure, without starting engine, with wheels chocked on level ground and foot off brake pedal, release parking brake and listen for air leak. Then press brake treadle, then listen again for air leak. I have used a stethoscope with a long plastic hose in a long 1/2" PVC pipe to direct hose to listen to leaks. If no stethoscope, just put end of plastic hose near ear.

Re: Air loss-only when driving

Reply #22 – July 07, 2014, 12:44:25 am

Joe, I had the same symptom as you. A relatively rough highway was thought to be the problem, frequent adjusting as drove. I insisted that not sufficient. Mechanics checked it out, was leaking ride high control valve....maybe two as I recall,

Not to say that your problem, but that behavior was mine.

After that fixed, my cycle time back to about five minutes

Mike

Re: Air loss-only when driving

Reply #23 – July 07, 2014, 08:38:17 am

Quote from: Lucky1 – July 06, 2014, 11:23:23 pm

So, tomorrow Karen gets the soapy water task while driving down the highway.

No matter how I read that, it sounds dangerous!

I have visions of Karen securely strapped to a frame member (using Duct tape?) under the coach, applying soap solution to fittings as you cruise down the highway.

She must be a VERY adventurous lady!

Re: Air loss-only when driving

Reply #24 – July 11, 2014, 10:47:06 pm

I read that the same way,

Karens disguise is shot, She is Wonder Woman,

While Joes driving and Barreling down the highway, Karen gets a bit Bored with it all,

So what could be more entertaining for a Wonder Woman than checking out the problems with the air lines under the Coach while its moving,

Just another uneventfull day for her, Hahahahaha

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