Air System Problem

Hey y'all! I've got a 2012 KW T700 with Cummins ISX 450 and a Bendix AD with large cartridge. I admit, I don't know enough about my air system as I should, but let the learning begin!

I am having an intermittent problem with the air system's ability to build properly. Most of the time, it'll charge to 120psi with no prob. The problem is, after the pressure falls past 100, it doesn't start building like it used to. Sometimes, I'll lose all pressure. Then again, sometimes, it all works just fine. I know the cartridge needs to be replaced soon, as I have not had it replaced in the 125k miles that I've had the truck (total mileage is 505k).

Thanks to guys like Rawze, I have learned a great deal of vital info to keep my truck out of the shop and money in my pocket! Any info to help me get this air system running right again would be much appreciated! Thanks y'all!

 

I downloaded quickserve. Looks like a handy app for finding cummins part numbers. I have been looking at TS diagrams for Bendix and air system. Looks like I'll need to stop at a shop and get a few things like springs and o-rings....and definitely a new cartridge.

 

I usually drain my air tanks and don't see any water. But I do see a good bit of water when the AD purges (at 120psi)

 

So, here's an observation I've discovered: my problem went away for a few days, but it just came back out of nowhere. Luckily, it doesn't happen while I'm driving. I noticed that when it fails to cut back in and my pressure drops below the cut-in limit, I can rev up my RPMs and bam, she cuts back in and the pressure goes right on up. So, is this more of a compressor problem???

 

Can't hurt! We'll see tomorrow.