losing air

capt mav · 04-10-2009, 12:30 PM

2000 winney journey freightliner chasis
Issue: Running down the road I lose air (about 20 pis in 10 minutes) air runs down till compressor kicks in and it then returns (front and rear).
This problem prevailed for many months. Then starting recently as I used brakes air would bleed down and not return. Not every time though this is intermittent, when air does stay down the only way to get it back up is to rev engine over 2000 rpm at this time it will recover. During this air loss the brakes get mushy, have actually had it bleed all the way to zero by pumping the brakes. Finally after sitting with coach lowered air bags wont re inflate when I start coach back up until I run eng up over 2000 rpm, at that time bags re in flate.... (6 months ago i had the rear bags replaced, not sure if any of this is related).. I have it at the freightliner service ctr right now where it has been for 4 days, they tell me they cant figure out the problem.... right now all they are offering me is a huge bill,, any ideas....

**Gary RVRoamer** · 04-11-2009, 08:42 AM

Obviously either a major leak or the compressor is not putting out much air to begin with. If the shop techs can't find it, I doubt if anybody here will be able to help much without even seeing it. Especially without any idea of what the service guys have already checked out.

Normally the compressor should be able to deliver air fast enough to keep the system fully aired up, even with a significant leak, but yours sounds weak. I had a major hole in my left rear suspension and it deflated within 10 minutes with the engine off, but with the engine idling it stayed right up where it belongs.

You did not distinguish between the front and rear air tanks. If you lose ALL air pressure in BOTH tanks, then the leak must be in the brake system. That's because the suspension air is supposed to be isolated from the brake air and not able to bleed the brake air tank (usually the front tank) below about 75 psi. If the air loss is rear (suspension) tank only, then the leak has to be in the suspension. At least that's how it is on my 268" XC chassis.

Jim Stewart · 04-11-2009, 02:53 PM

I just started losing air in one tank and found the problem. The accessory air hose was coroded and I had tried to force the nipple into it. The nipple would not go in, the crude did and it blocked the valve from fully closing. It would leak down about 20 PSI on the one tank and come back in when the cutout kicked in. Probably not your problem but worth a check.

bdpreece · 04-11-2009, 11:12 PM

Have you ever had the air dryer serviced?

SteveG · 04-22-2009, 07:32 PM

On our 2004 36G Journey I have a similar leak down on our rear air brakes, maybe not quite as quick, but certainly faster then our front brakes. I have limited air brake experience which means close to none. My air dryer is routinely serviced.

I found some air brake tests to run in a 2007, 3rd qt FL Chassis Owners Club quarterly magazine at this URL
http://www.freightlinerchassisowners...Qtr07final.pdf

This includes the air governor test, the static brake test, the applied brake test, low air warning test, emergency brake system test. All of these tests indicate that everything is working OK. I have yet had an air issue but it seems to me that I might be experiencing potential symptoms.

Because the test are OK my thinking is I can't have a leak. True or not true? I have gotten myself underneath to try to see if I can hear a leak but nothing so far. Any ideas? Or just leave well enough alone? Thanks, SteveG

**Gary RVRoamer** · 04-23-2009, 08:35 PM

Those tests do not prove you do not have an air leak, brake system or elsewhere. As long as the compressor can keep 65-75 psi in the brake air tank, your coach should stop normally. The compressor may be running full time to do it, but it will stop.

Besides, the leak may well be in the suspension, which merely bleeds the tanks down from 125 psi or something less but still at least the 65 psi needed to keep the brake system operational.