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chunker · 09-20-2017, 08:54 AM

Last month I had an air system failure on the road and had it towed to Freightliner in Yakima WA for repair. The problem was the air dryer controls and governor (see previous thread). For a while I have had a leak of some sort in the front air as indicated by the gauge. The symptoms were when dumped and leveled the front air would drop to below 65,( usually hold around 50+-), and it would take a few days. When not dumped it held pressure.

I'm home now and parked back under the pole barn and when dumped the front air loses all pressure over night. Last night aired it up and let it sit not dumped and this morning the rear is squatted and front air gauge is around 60. It sat over night for around 15-16 hours. I have a Freightliner chassis air lines diagram but can't find the gauges in the diagram. I'm a little confused because I would have though the "front" air would supply the front suspension and the "rear" air the rear suspension. The diagram labels the rear service tank as primary and front service tank as secondary. The diagram also shows the air from the compressor goes first to the primary tank, then to the secondary. As far as where air goes from the tanks, it appears that the primary supplies the rear suspension and secondary the front suspension but there are manifolds in the system so exactly tracing air flow is difficult without knowing the functions of the manifolds. Both air tanks appear to provide air for the brakes.

Now the problem of finding the leak and where to look first. I have wooden ramps that will raise the whole coach 6" which is enough for me to crawl around underneath without being squashed if the air dumps. Unfortunately 45 years of helicopter flying has left my hearing rather poor and my hearing aids amplify all noises, background included. I may ask my girlfriend to roll around under it but hate having her in that position.

When I got towed it was on a low boy trailer. The tow driver connected his air supply to one of the tanks, not sure which, and aired it up long enough for me to drive on the lowboy. He connected at one of the pull drains. I'll check there to make sure it was put back on securely but does anyone have ideas where to start and what the most likely causes are. I have spent a fair amount of time under the coach previously lubing and adjusting ride height and have not heard any leak, but apparently what ever leak is now much worse. I will mix up a soap solution in a spray bottle but would rather not "wash" the whole underside.

Thanks in advance and I promise to update with results and findings.

CountryB · 09-20-2017, 09:12 AM

Just take a spray bottle with water and a few drops of dish detergent to make soapy solution and spray the fittings and valves. The bubbles will show you what is leaking.

With air brakes there are two air systems a "primary" and a "secondary" like the split hydraulic brake system on your car. So if one system fails you have the other to stop with. It is not setup for front of vehicle air stuff and rear of vehicle air.

Go to airbags and trace the air line to the bag leveling (ride height) control valve, see if the valve is leaking. Should look something like this.

chunker · 09-20-2017, 09:17 AM

With air brakes there are two air systems a "primary" and a "secondary" like the split hydraulic brake system on your car. So if one system fails you have the other to stop with. It is not setup for front of vehicle air stuff and rear of vehicle air.[/QUOTE]

The gauges on the dash are labeled front and rear. Normal pressure is 120+- and the low pressure alarms at below 65psi.

CountryB · 09-20-2017, 09:25 AM

Quote:

Originally Posted by drwwicks

With air brakes there are two air systems a "primary" and a "secondary" like the split hydraulic brake system on your car. So if one system fails you have the other to stop with. It is not setup for front of vehicle air stuff and rear of vehicle air.

Quote:

The gauges on the dash are labeled front and rear. Normal pressure is 120+- and the low pressure alarms at below 65psi.

on a split system the "primary air" is for rear brakes and the "secondary air" is front brakes. At least on a semi-truck, that's the way it works.

chunker · 09-21-2017, 03:31 PM

Resolution. Armed with my soapy spray I crawled around under spraying everything that looked air. The secondary air tank purge drain was leaking. That is the one that the tow truck driver removed and connected his air supply to air up for the tow. I first tried to tighten but without much success so I drained the tank and and removed the valve. The threads in the tank didn't look very good and the threads on the valve, brass part, were a bit distorted and stretched. Used a 1/4" NPT die to clean it up and a tap to clean the tank threads. Some teflon tape and pipe dope and the valve went in smoothly and held air. Tank actually seemed to come up to correct pressure quicker than the past.

Several hours sitting and pressure held. I now have it dumped and will see if there is any other point of leaking but so far so good.

pbucha · 09-21-2017, 04:12 PM

Nice work!

ladagobago · 09-21-2017, 05:04 PM

Just a note: I once had a valve stick open slightly after a periodic pull on the drain cables. It could have been a small particle but as soon as I jerked the cord a few more times it stopped.