View Full Version : Air leak(s)

04-14-2016, 10:30 PM
My 99 Vantare H3 does not lean or sink down over a day or two but after about 30 minutes the aux pressure goes to zero and about 3-4 hours the other pressure gauges go to zero. Where should I be looking for leaks? Thanks, Cliff​

dale farley
04-15-2016, 10:03 AM
I'm sure others will have more definitive answers, but with that kind of leak, you should be able to walk around the bus when you shut it off and hear the leak. Without getting under the bus, you should be able to check the area around the auxiliary air compressor and the area with the norgren valves in the front of the bus. You may be able to hear a leak in the rear by just getting close to the wheel area.

04-16-2016, 10:42 PM
Cliff, welcome to the inevitable world of air leaks. The first thing to determine is whether the leaks effect the safe operation of the coach. You should perform a DoT brake test. Follow that with a driving test. When driving, do the Primary/Rear and Secondary/Front gauges stay close to a steady pressure when not using the brakes? If so, the leak(s) are as important as you want to make them.

Likely the most common source of leaks is rubber o-rings that have simply aged. These maintain the seal in the push-on fittings used throughout the coach. They are also used in the air relay valves, commonly referred as Norgren valves. Other sources of leaks are leaking brake canisters, air tanks, and defective protection devices.

The other problem that makes troubleshooting difficult is the likelihood there is more than one problem. Your symptoms suggest your coach has more than one problem. The good news is that your air bags and control valve are good. When the ignition key is off, an electrically controlled air valve locks the air in the bags, isolating them from the rest of the aux system.

Aux air leaks are commonplace. Unless severe, you might want to save troubleshooting the aux systems for a rainy day.

There isn't a single item that can cause the aux and 2 braking systems to all leak down. Between the Prevost aux air tank and the aux water separator is a protection valve. This valve only opens when either side of valve has about 60psi. When the aux and braking systems drop below 60psi this valve closes. This means an aux leak shouldn't bring the braking systems down below 60psi. You might want to cap the aux line at the aux water separator and then air up the coach and see if the pressure still drops in the braking systems.

The parking/emergency brake valve is an easy thing to check on the braking system that does leakover time. The only things that are common to both braking systems is the brake or treadle valve and the double check valve located near the treadle valve.

Some leaks are easy to find though their obvious sound or by applying a soapy solution to the leak. Others can be difficult. Some leaks are internal and more difficult to troubleshoot, like the protection and check valves. The biggest challenge for most of us is accessing the under carriage components. Obviously, don't crawl under a coach that is not held up by jack stands or other safety devices.