Dumping air bags

I honestly don't know how big of a leak will get you a ticket, but to be placed OOS you have to have a big enough leak to not be able to maintain 90psi at idle. That is a pretty big leak, and way above the 3 psi per minute test.

Also, a truck that leaks down within a few hours can still pass a air brake test. I'm guessing most of you that claim a truck should hold 60 psi for days on end must drive new trucks. All of our trucks are older, and will pass a air brake test, but you will drive yourself crazy chasing every little leak. The fact is, if somebody with good ears can walk around a stopped truck and not hear any leaks, the system is in pretty good shape. If you can hear it, it needs to be fixed, but to go all over the truck with a soap bottle looking for every little bubble will drive you insane.

 

It would be interesting to know how much really is a 3-psi-per-minute leak converted to idling. Then there is the 4-psi-per-minute leak for the brake application. A leak that can be heared or a truck that cannot maintain over 100 psi while idling is a really big leak. Lots of older trucks (4+ years) that haven’t been maintained properly when it comes to air leaks, will have leaks all over the place. So expecting to come to the day when you can hear the air leak may not come as leaks are usually scattered and collectively create a big leak. I have a 2014 Freightliner Cascadia with 722k miles. It is very common for my truck to still have air in the system (70+) after a 10-hr break and even a 34-hr break. If it’s very cold outside, sometimes my truck goes under 70.

 

I drove a 2000 FLD starting in February of 2007. It held air over the weekend except one that was super cold for where it was. My current truck, due to it having a bad brake pressure switch, I would only use the trailer parking brakes, and overnight it would still have enough air to keep the tractor brake from popping. That's in a 26 year old truck.

I have never driven a Volvo, even one less than 5 years old that would hold air for more than 90 minutes!

 

I always thought about those trucks parked next to me at night idling with the air dryer poping off every couple of min would be something dot would pick up on pretty quick cause to me that's a sure sign u got a pretty good air leak

 

Not at all. They drier has gone bad, and they're constantly purging what little moisture there is. They can't build enough pressure to keep up with it if they were cycling because of an air leak.

 

That's just a broken governor. It might be popping off the tank pressure safety valve.

 

Yeah I agree. Just had valve replaced on my ad9. Truck was sneezing every 45 seconds with no air leak

 

Well, I hate to disagree, but I recently had this same problem, which I fixed myself (with the help of this site and YouTube). It is an air leak, but the leak is not constant. Sometimes it leaks a lot (through the purge valve) and sometimes only a little. This is absolutely a safety issue. I had to pull over 2 times on the freeway because the leak was so bad my PSI was going under 70. Another time in temperatures under zero, it took my truck a few minutes of idling to finally get it past 100 PSI.

The mechanic who diagnosed the problem told me it was only the purge valve, but he recommended replacing the entire air dryer. In my truck that includes the governor. They didn’t have the part in stock, so I kept rolling and fixed it days later.

 

Your standard “run of the mill” truck air compressor will pump around 7cfm at idle. I don’t know how that converts to psi, but that is still a pretty big leak for a compressor not being able to keep up.

 

That's like a 3/4 rattlegun.