Air bag/leveler / ride height problems on heavy loads???

No enough air pressure to the ride height valve. There is a pressure protection valve that will cut off the air bags at a certain pressure to protect the rest of the truck from loosing air in the event of a blown air bag. If the valve screws up it could only be letting a few psi back to the air bags, which is enough to lift the suspension empty, not enough when loaded.

 

Sometimes they screw direct into the air tank. They are 2' long and about an inch across. Some have a round part on one end. Tap it gently with the end of a screw driver and see if you can get the air flowing.

 

You won't have any where near 100 psi in your suspension. More like 60/70 depending on type of air ride and weight on drives

 

You would have to remove the supply line to the ride height valve and put an air pressure gauge on the line and see what pressure is available to the valve. I was working on a 2000 9400I today. The pressure protection valve for it was plumbed at the second supply port of the rear service brake relay valve.

 

Good question, LOL. You know, I really can't remember ever having to change one of those valves in almost 20 years. I think that valve may be closer to the ride height valve. Screwed into the tank is one spot it could be too. Like I said in the last post, I saw a truck a few years older than yours today, and it had the protection valve about 1 foot from the ride valve. International doesn't have air line schematics like they do with electrical, so I really don't know where it would be. Basically the valve should allow no pressure to the air bags until the system pressure is up to about 70 psi or so. Not sure on the exact pressure, somewhere in that neighborhood. Once the pressure is up high enough the protection valve will open and allow system air to the ride height valve. So technically, if you have 100 psi in the tanks, there should be 100 psi at that valve. The valve could be stuck partially closed and only allowing 10 or 20 psi to the air bags, and that would explain why it can't raise a loaded trailer to the correct height.