Stranded in Georgia

[Nadge]

Originally Posted by ga traveler

I should have said the rear brakes are spring operated. On all the motorhomes with air brakes I worked on, the rear brakes were the parking brake. When the park brake was pulled the air was bled from the rear brakes and the rear brakes were applied by a spring in the chamber. Also if the pressure dropped below 60 psi the brakes would come on.

Are you correct in saying at 60 PSI the rear brakes would engage?
If so, then at what pressure does the low brake air pressure warning alarm sound on your rig?
My 2016 Newmar Ventana LE 4037 brake low pressure alarm comes in at 60PSI and brakes don't automatically engage until pressure drops to 30 PSI allowing you to time your absolute must stop now before the immediate 30 PSI brake lock up occurs.

[jacwjames]

With that air loss you should be able to hear a leak. If you are traveling with someone can they work the brake pedal with the engine running while you listen around the perimeter of the coach without getting underneath. With the engine off can you hear anything with and without pressing the brake pedal.



I have a different coach/chassis but I assume (yup big assumption) that most of these systems are similar in that the system has safety features that would prevent catastrophic air loss so that the brakes would still work in an emergency. Mine does, each air bag and other auxiliary circuits have a pressure protection valve in them so that if a line is tore loose it doesn't let all the air out of the system.

For you to be loosing all air you have a major problem that may start back at the air dryer.

[Roland Trombley]

I think that the mechanic is concerned that the unloader on the compressor may be sticking intermittently, alternately both on and off.
Any thoughts on this?

[mackwrench]

Originally Posted by Roland Trombley

I think that the mechanic is concerned that the unloader on the compressor may be sticking intermittently, alternately both on and off.

Any thoughts on this?

I think you have a leak. The air suspension dump valve is plumed into the power gear leveling system....some chassis have a dash switch that will dump suspension as well.

Since you're having supension losing air issues all once I'm suspicious of the dump valve. It's located just behind the front axle, kinda hard to access and be very careful getting under coach...if suspension loses air it could kill you!

So.....do you have a suspension dash dump valve? If you turn on/off leveling system does suspension go down/up?

The failed dryer has probably worked it's way up to the dump valve....but it can also be bypassed. Just make sure the coach is supported on jack stands.

[Roland Trombley]

Sounds reasonable. He is coming back later to do more checking.
Yes, I do have a switch on the dash labeled "air release" that appears to work correctly, but I'll ask him to check it.
I am beginning to think this problem may be associated with the air suspension.

[wolfe10]

Originally Posted by Roland Trombley

Sounds reasonable. He is coming back later to do more checking.
Yes, I do have a switch on the dash labeled "air release" that appears to work correctly, but I'll ask him to check it.
I am beginning to think this problem may be associated with the air suspension.

Yup, possibly a piece of the desiccant keeping the dump valve from seating.


But, you should be able to hear that massive an air leak.

[mackwrench]

Work the power gear leveling system on/off as well.....it should automatically dump when system is on.

[ga traveler]

Originally Posted by Nadge

Are you correct in saying at 60 PSI the rear brakes would engage?
If so, then at what pressure does the low brake air pressure warning alarm sound on your rig?
My 2016 Newmar Ventana LE 4037 brake low pressure alarm comes in at 60PSI and brakes don't automatically engage until pressure drops to 30 PSI allowing you to time your absolute must stop now before the immediate 30 PSI brake lock up occurs.

I did not say 60 psi, I said below 60 psi the brakes would come on. Different chassis manufacturers have different pressure settings. Some 30, some 40 etc.

[8v8tor]

Sitting still with the brakes released and your tanks full engine off, have someone walk around the coach outside at each wheel position and listen while you apply the service brake. Wondering if you might have a bad pancake in one of the chambers. Wouldn't have anything to do with air intermittently not building pressure, but could be where your air is going while driving. That goes back to the governor, and or unloader. I know it is an apples to oranges comparison as my class 8 truck runs most every day and doesn't sit for months at a time, but my current truck went 1.6 million miles on the original compressor. Changed it when I did the inframe overhaul, but it was still working fine. In over 5 million miles I've not had a compressor fail, governors, dryers, valves, and chambers yes.

[mackwrench]

Originally Posted by 8v8tor

Sitting still with the brakes released and your tanks full engine off, have someone walk around the coach outside at each wheel position and listen while you apply the service brake. Wondering if you might have a bad pancake in one of the chambers. Wouldn't have anything to do with air intermittently not building pressure, but could be where your air is going while driving. That goes back to the governor, and or unloader. I know it is an apples to oranges comparison as my class 8 truck runs most every day and doesn't sit for months at a time, but my current truck went 1.6 million miles on the original compressor. Changed it when I did the inframe overhaul, but it was still working fine. In over 5 million miles I've not had a compressor fail, governors, dryers, valves, and chambers yes.

+1 good advice.

[Roland Trombley]

Six different mechanics have looked at this. 4 of them didn't want to be bothered trying to fix it. Local truck shops don't work on motor homes.

Yesterday's test ride was fine for awhile, but lost pressure to the air bags at 3 miles.

I'm about at the end of my rope.

By the way... No sign of any gray powder anywhere

[mackwrench]

Originally Posted by Roland Trombley

Six different mechanics have looked at this. 4 of them didn't want to be bothered trying to fix it. Local truck shops don't work on motor homes.



Yesterday's test ride was fine for awhile, but lost pressure to the air bags at 3 miles.



I'm about at the end of my rope.



By the way... No sign of any gray powder anywhere

I know it's frustrating!

....if you lose air suspension to both front AND rear axles, then dump valve is leaking or stuck open...each axle has it's own ride height valve. Only the dump valve ties them together on this chassis.

You say you have a dash air suspension rocker switch, with air psi up at set point, like 120, shut engine off, turn key on and turn suspension dump switch on/off several times waiting a few seconds between. You should hear the dump valve "spit" (exhaust actually) air just for a second in the "up" position, and steady air exhaust with it in down position.
This dash mounted dump switch is an electric switch. I've seen them fail in heavy trucks where they'll intermittently dump the suspension. You may can get suspension aired up and disconnect the wires at back of dump switch...

Let's get a little more info on this...

When you park, does suspension stay aired up for a while?

During today test drive did air tank pressure drop along with air suspension?.....if you'd lost enough air parking brake would had applied on it's own...

again, I'll ask is the suspension lowering/dumping air when the leveling system is turned on?

When it builds up air pressure parked, you should still hear air exhaust from governor, just like it did when dryer was hooked up.....once it builds up to set psi, can you put your finger or hand over the smaller line from governor to dryer and feel any air continue to come out?

[Roland Trombley]

Thank you so much for all of your help. I'll try to answer your questions now, but since it is dark I will do your additional prescribed testing tomorrow.

Originally Posted by mackwrench

I know it's frustrating!


....if you lose air suspension to both front AND rear axles, then dump valve is leaking or stuck open...each axle has it's own ride height valve. Only the dump valve ties them together on this chassis.

I think front and back were both down. The front was for sure, but will check tomorrow.

You say you have a dash air suspension rocker switch, with air psi up at set point, like 120, shut engine off, turn key on and turn suspension dump switch on/off several times waiting a few seconds between. You should hear the dump valve "spit" (exhaust actually) air just for a second in the "up" position, and steady air exhaust with it in down position.

I will check this tomorrow.

This dash mounted dump switch is an electric switch. I've seen them fail in heavy trucks where they'll intermittently dump the suspension. You may can get suspension aired up and disconnect the wires at back of dump switch...

Let's get a little more info on this...

When you park, does suspension stay aired up for a while?

Yes, it stays up for hours.

During today test drive did air tank pressure drop along with air suspension?.....if you'd lost enough air parking brake would had applied on it's own...

The tank pressures both dropped. I got nervous when it started to go below 80 and pulled off the road. Both gauges were around 75 and the air bags down. As I sat there the suspension aired back up. I drove the 3 miles back to the campground with the gauges reading around 90 all the way. The terrain here is all hills and curves, campground has horrible steep hills and turns abd bad bumps, it is even difficult to drive in my Cherokee. But I made it back to campsite with 90 pounds air. By the time I got ready to level i had 115 pounds.

again, I'll ask is the suspension lowering/dumping air when the leveling system is turned on?

Yes it is

When it builds up air pressure parked, you should still hear air exhaust from governor, just like it did when dryer was hooked up.....once it builds up to set psi, can you put your finger or hand over the smaller line from governor to dryer and feel any air continue to come out?

This evening before dark I did some stationary testing, with airbags dumped and with them full.
Both gauge slowly build 115 to 120 pounds but no exhaust from air dryer.
I pumped pressure down with brake to 55 pounds to bring the alarm on, both ways, and it consistently, quickly recovered and stopped the alarm. I timed 80 to 100 pounds over and over and over and it takes 20 seconds, with and without airbags.

[Roland Trombley]

Originally Posted by mackwrench

I know it's frustrating!

You say you have a dash air suspension rocker switch, with air psi up at set point, like 120, shut engine off, turn key on and turn suspension dump switch on/off several times waiting a few seconds between. You should hear the dump valve "spit" (exhaust actually) air just for a second in the "up" position, and steady air exhaust with it in down position.

This morning I tried this test... suspension aired up and key on, engine off. Operating the switch has no effect without engine running.

With engine running, press at 115, dumping produces heavy whoosh pushed and stops as soon as switch is turned up.

Pressures holding at 115 since I did this 1/2 hour ago.


Do you know of the. Compressor unloader is serviceable on these?
My mechanic is leaning toward Compressor unloader sticking, but is afraid the whole Compressor must come out. He is trying to help me avoid this.