AIR Leak - HELP!

[DebnDan]

Thankfully my brakes locked up in driveway after 800 mile trip. Air pressure would not build up. Air is gushing out of the valve in the first photo. The second photo is the canister this valve is attached to. I assume this "canister" is part of the air compressor... or is it the dryer I keep reading about? Have had 5 gassers before this DP which I purchased a few months ago - there is a learning curve going from gas to diesel. At any rate I assume I can go to a Cummins dealer and purchase this valve and replace it. Any info from this group would be most appreciated. Right now I am parked in the driveway with locked brakes. Thanks in advance for any of your help.

Dan Callahan
2008 FW Excursion
2007 Freightliner, 360 Cummins and Allison

[Gary RVRoamer]

It's not really a Cummins part, but most any Cummins Coach Care facility could fix it. Or most any heavy truck shop. The air system is part of the chassis, so its a Freightliner component, though they undoubtedly sourced it from one of the major truck component suppliers.

That looks like an air dryer cartridge but could be part of the air pressure regulator too. The valve itself may be simply doing its job, as a result of some other failure. Maybe a clogged air dryer (no air gets through). Has the air dryer ever been serviced? A 2008 should have had the cartridge changed at least twice (usually a 36 month interval on late model DP's).

[jergeod]

The second photo is your air drier, you can replace the valve but if you haven't been draining your air tanks on a regular basis the inside of the drier is fill of gunk and a new valve won't last long. I myself would replace the drier with a new one, drain air tanks then drain tanks once a week while in use. If unit has been stored, when you get it out run the air up then drain the tanks, condensation will build up while sitting. If you have alot of oil blowing out the drier or the tank valves when dumping now you need to look at the air compressor because that is where the oil would be coming from.

[DebnDan]

I have owned the coach for 4 months. Based on it's condition I assume it was maintained, however I doubt there are many people crawling underneath and draining their tanks. I will get under and try and locate the tanks this evening. I think what you guys are saying is take the tank apart, clean it and the fittings up and then replace drying cartridge. If there is still a problem I should have a mechanic look at it. Correct?

[no3putt]

on our Freightliner Chassis by the behind front wheels, there are three lanyards to pull, two on one side and 1 on the other. to drain the air tanks, pull the lanyards and when tanks have air you will hear air come out.

[Darrel]

Dan - your approach is what I would do also. When they speak of emptying the tanks (especially after your valve stuck) there should be some cable lanyards connected to each of your air tanks. Pull on them and the tanks should purge. Watch to see if any moisture comes out which could indicate other problems.

Have a nice day - Darrel

[twinboat]

The part that is leaking is the Air Dryer safety valve, used to protect from over-pressure. You need to find out why it blew.

The air dryer is installed to eliminate the need to drain your air tanks often. It is still good practice to drain all of your tanks a few times a year.

The order of components is "Engine mounted Compressor", "Air Dryer", "Wet tank" and then 1 or 2 "Dry tanks". Sometimes 1 of the tanks is a dual tank, so it would have 2 drains.

The line from the Air Dryer goes to the wet tank fitting, that has a check valve in it, to hold the air in the system, when the compressor stops pumping.

From the wet tank, there is a small line that runs back to the governor, that is mounted on the compressor. If that line is leaking, the compressor will not stop pumping, causing the safety fuse to blow.
There is also a small line from the governor to the Air Dryer, that sends a signal to the air dryer to open the un-loader valve, whenever the set pressure is reached. If that line is leaking the compressor will cycle often, with the air dryer un-loading every few minutes.
Another reason for an Air Dryer cycling, is a leaking wet tank check valve. As the wet tank air leaks back thru the Air Dryer exhaust, the pressure drops and re-starts the compressor.

The pressure gauges you see in the cab are hooked to the 2 dry tanks, so, even though the pressure looks normal, the wet tank could be leaking because there are other check valves to protect your air supply when something goes bad.

Hope this helps

[Dutch Star Don]

"twinboat".....nice/helpful description of system in easy to understand terms.

[Larrikin]

Replace the entire drier unit. It can be done in your driveway by a Mobil truck tech who knows his stuff. Call Freightliner in Gaffney SC with your VIN number handy and they can give you the correct p/n for your coach. The big unit should be replaced every 5 years, filter in the unit is changed on a 2 year cycle.

I had this failure in Upper MI 3 years ago, got it fixed on site in an hour. Part came overnite, but you may have one available in your area. As I recall, it was about $300 for the unit (Haldex).

Good luck, it's easier than you may think.

[Coma]

Haldex pure air. Two service kits upper and lower. The overpressure valve should not be operating that way. It may be clogged with the coalescent effluent.

[DebnDan]

Thanks everyone.... I found the 3 valves and emptied the tanks, no moisture to speak of. Is it necessary to take the whole dryer unit off to change the cartridge. I think I want to try that first. I assume the cartridge is dropped in from the top. But maybe I should take the whole unit off the coach to see if it needs cleaning or do as Larrikin suggests, just replace the whole thing.

[DebnDan]

BTW, I am not trying to be a pest or cheap, I really want to learn all about the air system. Coming from gassers this is all new to me.

[twinboat]

Get a fitting to connect the 2 bigger hoses together and plug the small one.

Start the engine and watch the air gauges. If they climb, make sure they stop before they get to 130 pounds. If they keep climbing you have other problems. If they stop and hold 120 pounds, there is a blockage in the dryer.

You don't NEED an air dryer. You can jump it out of the system, just remember to drain your air tanks often, until you put one on.

Hope this helps

[DebnDan]

Good news... I bypassed the dryer as suggested and all is fine. The coach is now drivable. The issue is in the dryer. Probably going to winterize and put in shop for routine chasis and transmission service and have the dryer handled there. Thanks everyone for all your help.