Lost air to brakes and air bags

[Probasco]

Stopped over in Klamath Falls headed home from Reno Thanksgiving. Packed up in the morning but the air alarm never went off, no air being pumped into tanks. Without air you can't move it. I climbed under it and purged the tanks which exuded gooey snot like substance and then some air. Tow guy used a pump from his rig to mine so it could be moved. Ended up towing it to Medford, Or, (thank you AAA) to Cummins where they replaced the air pump governor. I drove it home (6 hours) without a problem. Stopped to top off the fuel before parking it and the air alarm started and stayed on until I parked about 3 miles later. I have noticed for the past year it hisses when I stop and park like its letting out air. Thought it was just a quirk. It is a 98 Discovery on a freightliner so it has some seasoning. Any ideas on what the issue might be? Could the air bag(s) be leaking? The fronts pop loud when filling. HELP!!!!

[nothermark]

Does it hold air if you air up the system with a separate compressor?

If the pressure drops as soon as you stop the separate compressor and continues to drop you have a leak problem. If it airs up and stays up it sounds like a compressor problem. That is assuming the system acts the way you said it did.

What I wonder is if the gunk you talked about came from the compressor and fouled the new governor.

[RRR]

The snot like goo was it dark grey or blackish in color? How often do you drain your tanks? Seen this stuff before?

You likely have an air dryer, when was it serviced last? It sounds like the purge valve may be sticking. Should make a loud ppssssttt when the air reaches the cut-off point of about 120 pounds then stop.


Sending you a PM.

[RoadDogYVR]

Black/grey snot-like goo in air reservoirs is compressor oil blow-by mixed with general condensate "ick" from in the tank.

Forgive me as I'm a trucker with no motorhome experience but I do know a thing or two about air brakes...

Do you have multiple inline air tanks like we do in the big rigs? We call the first in line after the compressor the "wet" tank and all subsequent tanks "dry tanks" for a reason. Even with an air dryer, you get get some oily stuff through and frankly routine draining of air tanks all the way to empty is highly recommended. You need to dry to empty to get the bottom sludge out - just "blowing down" tanks isn't enough to clear the crud.

[Probasco]

i purged before the new gov was installed, but maybe the line has some residual

[Probasco]

Not sure, I have 3 tanks, and i think 3 dryers. 1 tank near the compressor, two up front

[Probasco]

Anyone have any experience changing the compressor? I plan n tackling it myself but wondered if there are any shortcuts or long cuts for that matter..


Thanks

[twinboat]

Originally Posted by Probasco

Anyone have any experience changing the compressor? I plan n tackling it myself but wondered if there are any shortcuts or long cuts for that matter..


Thanks

Call a mobile truck repair service before you start tearing the engine apart. Compressor failures are rare.

You need someone to troubleshoot your problem.

I worked on diesel powers stuff for 35 years and changed 2. Both on Cat powered machines, due to a spline defect.

[Probasco]

Cummins gave it a $450 diagnostic and said the compressor is toast. Despite that, if i air up the tanks with a shop compressor, then it starts working fine until i use the brakes a lot then the pressure drops. But it works fine driving around especially on the freeway.

[Probasco]

it has a new governer, but not enough power to fill up the tanks. The coach only has 70k miles but maybe the 1998 vintage has resuled in line leaks?

[nutcker]

Google how to clean the compressor unloader valves, not the governor but the unloader valves in the compressor that the governor opens when tanks are full. Compressors almost never go bad unless they start pumping oil. pretty common for unloader valves to stick,

[Unplanned Tourist]

Crawl under your rig with a squirt bottle filled with soapy water.
With the engine running and building air pressure, spray everything in the air system you can find.
You will see the bubbles any place there is a leak.
If no leaks, it could be your compressor.
Good Luck and Happy Glamping.

[Dale70]

With even small leaks you should not see the issue you are having.

My vote is the dryer unloader or less likely the Air compressor.

As was mentioned in an earlier post -- you should only hear the "Shoosh" sound when the dryer has reached pressure (generally 120-130 PSI) and then the compressor stops. The compressor starts again when the pressure falls below a certain number -- (typically 75-85 psi) That sound should only be occurring every 5-10 minutes with the engine running and the air bags up and not putting on the brakes.

thx Dale

[RRR]

Post #9 the OP stated Cummins diagnosed a dead compressor.