Air tank leak?

There is a leak in one of the brake systems. There are two, primary and secondary. Some accessories work of one, and some work of the other. For example, the horn could work of the primary, and the suspension of the secondary. Although I have driven trucks that held for several days, many, especially Volvos, wouldn't. Volvos won't hold air for much longer than 1 hour.

 

Listen for air leaks after you shut the truck off. You will have to be in a place where other trucks are not running so you can hear the leak. You will find it eventually. The fittings that air lines plug in at get worn out and air lines that are chafing/rubbing will eventually leak. Air fittings are anywhere between 5-25$ each. most in the range of 6-12$ Fleet supply store is best place to get these fittings.

 

How old is the truck? On my 96 I had an air tank rust thin and would leak. Or could be a leaking air bag on suspension.

 

My mack will hold enough air to not set the buzzer off for 3 days, the old mack will leak down to 0 overnight, the volvo i had been driving would set the alarm after a few hours....

Soap/water mix in a spray bottle and have at all the connections and air lines....you'll find the leak

 

Glass cleaner works great too

 

Air leaks are all to common. That said, if one system drops to zero in less then 24 hours, or less than an hour specifically, that would concern me if I was driving that truck. I will not go into the standard inspection brake check process, but there are things you can do to isolate the area where the leak may be located. In my case, the trailer itself or glad hand seals was a common source. Determine which system, primary or secondary is used for the trailer. (A good thing to know.) An easy way to confirm that is to set both the parking (tractor) and trailer brake, pump down the foundation (foot) brakes until both systems are empty. Start truck and let engine charge air tanks until cut off. Then with engine at idle or off, and all brakes set, release the parking brake (tractor) only and watch which system primary or secondary drops as the spring brakes fill and release. Usually it's the primary. Then reset the parking brake. Next release the trailer brake. Watch which system drops. Usually it's the secondary. If the system supporting the trailer is the one losing air, you can isolate if it's truck side or trailer side by setting the trailer brakes. If over 24 hrs, and the system stays charged, the leak is in the trailer side. If not, it's on the truck supply side. There are other things you can do to narrow down which other minor or sub system is leaking so your leak search with your ear and soap water bottle only needs to be in that area. Knowing where to start your search can make the job a lot easer.

 

It would be easier if you considered which system lost air.

If it is a red needle that went to zero it's your secondary, if it is a green needle that went to zero it's your Primary. OR vice versa. I cannot keep them straight in mind. A educated wild guess would be air ride bags consuming the air as the winds blew the truck over night. Rocking.

Anything else, I have to sit and think carefully. And before anything you need to go over the physical idea that you have a leak somewhere. Get a bottle of spray water with a bit of soap in it. Spray as you go along the entire system from your compressors and working back until see soapy bubbling from active leak or perhaps even hear it.

I can go on but I think AmericanRamber did a very good job here so... I just literally have to sit and wat for you to come back on.

 

I am going to add something else here. Experience is a good thing. By that I mean over time you learn things that help you take care of your truck. And by extension yourself.

One of those is to get to 'know' your truck and what things are normal in the way it works, sounds, smells, feels, looks drives and moves. That way, when something changes, you will pick up on it. The truck will 'talk' to you in many ways.

A lot of that is through the air supported systems. Learn to listen and understand what they are telling you. Do not ignore it. I found in a large number of cases, my truck would start indicating something needs to be looked at and maintained or repaired before if failed.

A couple of examples.

1) One time, (actually on more than one occasion) I noticed a lot more foot peddle travel was required and bigger chunks of air were being used on each brake application. Turned out a slack adjuster ratchet had failed on a brake chamber. This resulted in the loss of the use of one wheel brake as it would no longer activate that brake. It just stroked out.

2) brake peddle started getting spongy and gradually dropping. Initial brake check worked fine for spring brakes. But a diaphragm had failed on the foundation (foot) side and only leaked on foot application. This too was not all that uncommon.

3) was losing primary side air pressure when parked at times. Drove me nuts. Finally figured out It only did it when ignition was on and engine not running. Turned out the engine fan clutch was coming apart. With engine running, compressor kept everything aired up. Found that one just prior to total failure and fan going into radiator. I diverted to repair location in time. Found from talking to some other drivers and the shop that sort of thing would happen from time to time.

4) kept hearing multiple Phiffing and clacking sounds at times and sometimes when ignition first turned on. Also started getting a grabby wheel brake from time to time. Turned out one of the abs regulator air valves was failing. It happened more than once.

5) the air drier started discharging about every 20 to 30 seconds. Air system pressure stated fluctuating rapidly and over pressurizing about 10 pounds. The pressure regulator valve had failed. The over pressure safety valve was opening to release over pressure.

6) brake peddle started getting hard and stopping distances were getting longer. Air dryer started cycling almost constantly. Checked wet tank and a bunch of water came out of it. Very unusual for this truck. Prior checks alway had almost or no water. Engine air compressor was failing and was discharging coolant into air system.

7) running down freeway in middle of no where Nebraska and started getting wide fluctuations in secondary air system. Stopped to check out issue. Trailer air tank had cracked and was leaking badly at weld for drain plug bung.

8) hooked a transfer load trailer late one night. Everything all checked out. Spring brakes fine, tug test fine, foundation brake test fine. But when I started to roll and went to slow for a turn, brake peddle went right to the floor. Promptly hit hand brake, nothing! Hit foot brake again, went to floor, pulled parking brake. When I did that, trailer brake popped too. Then I went to figure out what just happened. Service brake line had a 6 inch chunk missing in trailer 5th wheel plate above drive tire! Turns out the area was plugged solid with ice and it had sealed the leak. When I started moving, the ice broke free and exposed the opening in the line. Hence massive leak. That is also when I learned the tractor protection valve actually works differently than I had been instructed! It takes them a while to activate! That is also when I added an extra check to
my trailer pretrip inspection. It was the first time I found exposed unshielded brake lines in that area. Every other trailer I had seen had a shield in that area protecting the brake lines. You could never see them. I encountered exposed lines in that area additional times on other trailers later on. And even found one other that was damaged on pre trip inspection. Fail!

You Want to avoid finding yourself broke down on the road somewhere.

Its always better to make repairs at times and places of your choosing than a forced shutdown in a poor and or dangerous location.

 

Tractor protection valves contain a double check valve. Trailer supply is supplied by whichever system has higher air pressure.