Volvo 780 Front air tank keeps draining!

Odd. Both of those should have leaked whether parked or not. Oh well, glad you found them.

 

This happens ALL the time midnight. It sucks that they used these plastic push on fittings and need to go back to certified brass fittings.

Glad you got it straight.

 

Air leaks are super annoying.

Today I heard my truck pissing air, sounded like it was coming from the air tank, it was I saw water bubbling from a puddle I drove through. Then I kicked a hole in it in my yard and told the shop to fix it. It was super rusty not my usual truck or I would have noticed sooner.

About the only time they will fix anything is catastrophic failure. It’s a joke. Half the time I go to the dealer with the company card and the owner doesn’t even get mad because he knows his shop is trash.

 

You can go to a salvage yard and replace all three now but get aluminium tanks this is a upgrade but they don't rust out

 

I've got the same problem - front tank leaks while driving...driving me crazy. Can't seem to find a air schematic that shows supply lines to the cab and rear leveling. Can only find brake schematics. Recently because of leaks have overhauled the dryer bleed - replaced both front brake ABS valves, front pass thru, parking brake control and replaced many a seal in the fittings (don't have front air suspension). I always repair leaks as I find them and have fixed MANY but can't find this one.....any other suggestions?
2014 VNL 780 D13....

Mark

 

On the driver side inside the frame in battery box area mounted plastic pressure protection manifold. Hard to find, hard to see

 

Great suggestion will check..it's been 2 years since I changed that LOL

 

This has been driving me insane also. The front tank (which I assume is the middle one) drops 20 pounds in one minute after the dryer purges. And then the compressor cuts in again. It results in a purge a minute, which is hell on the compressor and purge valve. I've been hunting leaks for an entire week. Mostly this has resulted in my changing lots of O-rings inside the brass quick-connect fittings everywhere, including the firewall pass-through. Tonight I found another leak on the tank from one of those black 90-degree elbows with an o-ring at the base -- maddening things they are, since they're metric and hard to find. If it weren't for this maddening leak, the most insane one would've been the one I could hear under the passenger side of the cab but never pinpoint. For a year or two I've heard it and listened for it and waved one end of a hose around with the other end on my ear, trying to pinpoint it. Finally I stuck the hose at the V-band clamp of the flextube after the 7th-injector diffuser, and the hiss got louder. Then I realized I had air in the exhaust! For a second I considered whether it was coming out of the air dryer and back into the compressor and into the engine and out of an exhaust valve, but no, of course, it was coming from a stuck valve on the hydrocarbon dosing module. In it, there's a fuel valve, an air valve, and an outlet to the 7th injector. If the system wants to send air to that injector, a solenoid clicks a valve open and away it goes. If that valve gets stuck open, the module will be sending air into your exhaust all the time. Then there was the leaky purge valve, the leaky Bendix valve near the dryer, which is part of the dosing system (this was a Bendix 280758, AKA a TR-3 valve, which apparently has been superseded by an RV-3 valve for $200 or somesuch cost. I merely replaced the old Bendix valve with a like part from ebay for $39). Then I thought maybe the O-Ring in the dryer's outlet check valve might've gone bad and let air from the wet tank back into the system (and then second-guessed that theory once I saw the diagram below suggesting there's no gauge on the wet tank -- after all, the governor is cutting in based on the yellow 3/8 line from the wet tank----). And so on. So guess what -- the only thing I've achieved is for this thing to hold air overnight! It still purges about once every 63 seconds at idle and once every 55 or 50 at higher RPM. And the rear tank still sits there with 125 pounds the whole time. But shut the engine off and it'll hold air at 100 just fine for an hour. Start it up and it leaks from 125 to 105 once a minute. The hunt continues . . .

 

Good info - keep us posted on what you find. I continue to have the same problem (I posted last June). For the life of me I cannot find the problem. After all this time I like you have noted that on the highway it does not go down quite as fast. I can't really tell if it's bumpy roads (suspension) or lower speeds and a
I-shift problem. Do you also have an I-shift tranny? As for that, I've checked the 90 degree fitting at the top of the tranny - checked for any air coming from the tranny - nothing. I've even tried sitting still and just shifting through the gears to see of it drops faster - NOTHING.