Community Forums

jeveler · 11-28-2021, 11:04 AM

Hi. I have a 2006 Newmar ventana model 3935, CAT C7 engineer, 330 HP. When I start my coach the air pressure for both front and back brakes remains at 25 lbs. as you may know I need a minimum of 65 lbs to release the brakes. Any thoughts where I should check? I’m in Davenport Fl at the moment. Any assistance would be appreciated. Happy post thanksgiving holiday. 703-362-2255 call/Text. Jeff

Warhorse6 · 11-28-2021, 11:12 AM

You don’t by chance have an air drain valve open? If not I would check the air drier filter housing first.

jeveler · 11-28-2021, 02:52 PM

Thank for providing me some direction. I’m fairly handy with tools and making repairs, but this my first time working on the air braking system Where are this parts you mentioned typically located on the RV?

Warhorse6 · 11-29-2021, 03:49 AM

I have a different model but most have an a drain release valve in the fuse compartment which should be in the basement below the drivers seat. I have others in my DEF compartment as well, but suspect you don’t use DEF so you might not have them. The air drier is a cylinder looking device with air hose lines running to it. It’s mounted near the rear axle. Best I can describe mine is its black, about 4 inches in diameter, and about 6 inches long. Easy way to check if it’s leaking is using some soapy water. Would get the air as high as I could, then turn off the engine and apply. Hope this helps.

gatorcq · 11-29-2021, 07:47 AM

There is a pressure relief valve on the dryer. Start engine and start listing. Put your jacks downs and raise coach a little so you can crawl under and look

wolfe10 · 11-29-2021, 07:57 AM

First, listen for an air leak-- build as much pressure as you can, turn off the engine and listen.

Next would be to replace the air governor-- not expensive or difficult to replace.

Other question is how long since your air dryer has been replaced/serviced? This is part of routine air system maintenance. Best bang for the buck is to buy a FACTORY reman (as in the factory that made it, NOT one of the many cheap "replaces .... ones). Not only are the filters new, but all the valves, heater, etc.

rvbiker45 · 11-29-2021, 08:33 AM

The first thing that I would do is verify that you really do not have adequate air. If you have the HWH leveling system, after starting the engine, push the STOW button on the touch pad.

After about 5-10 minutes of running the engine, see if the parking brake will release. If it does release, you have an indication problem that may be in the air sending units (usually two) that send pressure information to the gauges.

jeveler · 11-30-2021, 05:26 PM

Thanks for everyone’s feedback. I’m going back this weekend to work at a possible resolution to this building air issue. I’ll get under the coach and first drain the air tanks as someone suggested. Then I’ll start the coach to see if any air pressure builds. Then l I’ll move to the air dryer and governer (sp??)

jeveler · 12-04-2021, 08:30 AM

Sorry I’m not sure how to use this site to simply reply to the original tread. I let the air out of the 2 tanks. I notice one of the tanks sounded solid near the rear where there are 2 hex screws. Are these for drainage? They have some rust so I will spray with wd 40 and legit sit for a while until I defeat response to proceed or not.

jacwjames · 12-04-2021, 08:42 AM

One thing that has not been mentioned in the governor which actually controls when the compressor turns on and off to charge the air system. If it is not working you may not build air.

Do you own a small compressor. Usually somewhere on the rig there is a male connector that a compressed air source can be connected to. This is usually used by a tow truck driver but you can also use it to charge the system.

If you have a compressor hook it up & turn it on and see if it builds air.

Crawl underneath with a bottle of soapy water and spray all the connections going into the tanks. If you have air bags it may be difficult. Rule of thumb is not to rely on jacks for safety reasons. I made a set of 6 ramps that I can drive up on.

I had a problem with my coach loosing air and found all my PPV's leaking so I am in the process of replacing. The Pressure Protection Valve is designed to stop air leaking in the event of a line failure to auxiliary systems like the air bags. My air was leaking down overnight where in the past it would stay up for days. But what got me concerned was that when I stopped one time for ~30 minutes my air leaked down below ~60psi causing my alarm to come on. So I cut my trip short and headed to repair. In the process now, going to replace all 4 PPV's and one large diaphragm type check valve plus all the fittings.

amosnandy · 12-04-2021, 08:45 AM

Quote:

Originally Posted by jeveler

Sorry I’m not sure how to use this site to simply reply to the original tread. I let the air out of the 2 tanks. I notice one of the tanks sounded solid near the rear where there are 2 hex screws. Are these for drainage? They have some rust so I will spray with wd 40 and legit sit for a while until I defeat response to proceed or not.

If your coach sat and the air pressure went down to 25 psi but seems to be holding there you don’t have a leak. If pressure does not build with the engine running and you hear no leaks it is likely the compressor governor. The only other thing it could be is the compressor itself.

I’m not sure exactly where the governor is on a cat c7 but it should be right on the compressor.

One thing you can do if you have a portable air compressor is hook it up to the air line that should be in your generator compartment and see if you can get the air up above the 90# required to get the brake off.

While driving semi I replaced many governors

amosnandy · 12-04-2021, 08:49 AM

Quote:

Originally Posted by Tedo

You don’t by chance have an air drain valve open? If not I would check the air drier filter housing first.

If he had a valve open his pressure would be zero.

jacwjames · 12-04-2021, 08:56 AM

Quote:

Originally Posted by amosnandy

If he had a valve open his pressure would be zero.

There may be check valves in the system that may allow air to stay in the tanks but bleed out from other areas. Not sure on his coach but mine is set up that way.

The governor could be remotely mounted so that it can be adjusted and/or replaced easier. Mine is mounted on a cross member on the front of the engine (rear of the coach). In my case the governor gets it's pressure sense line from the front tank.

You almost need a chassis air schematic ( I have one for my coach) to know how everything is plumbed.

twinboat · 12-04-2021, 09:03 AM

If it's your governor, often replaced only because it's cheap, you can test for that.

Take the line from the compressor to the air dryer off and see if it's pumping air.

Before you do that, stick your finger in the air dryer purge valve hole. You should not feel air coming out of that, except when it gets to full tanks, and then just one big woosh.

No air coming out bottom of dryer, check for leaks along the line from the engine to the dryer. Most are a flexable steel braid. Heat and chaffing causes them to fail.

Don't start changing parts just because. It's to easy to mess up something and create another issue.