MackTech

You said it only drops air when the lift axle is in the up position right? If so it very likely will be on the lift bag portion of the lift axle setup.

I'm thinking since the air bled out the axle dropped and no air was put into the ride bags. I've seen that at the plant. Now if air was in there if question it. I'm thinking there is a leak at the ride bag quick release, the solenoid, or it's one of the lines between the solenoid and the quick release or between the quick release and the lift bags.

Prior to Volvo dictating air piping Mack piped lift axles to the primary tank with a pressure protection valve. I remembered when they changed it at the plant.

The valve in the pic you posted is one of the old style pressure protection valves. It will close when the pressure gets to low to protect against too much air loss which could seriously affect controlled braking. Once you lose too much air your yellow button will pop out and your spring brakes will lock up.

Did you replace the actual terminals in the connector or just the plastic part? The female part of the terminal could be losing connection. It's been too long ago since I worked on wiring to remember what circuit to look at, but if grounds are good, check the terminals.

I'm not sure when it changed but when a truck is made at the factory they put the net weight of the truck which is the weight of the truck without a driver, without a body, with minimal fuel (maybe 17 gallons). Removing the lift axles will reduce weight, but you need to check where they will be used that there aren't axle weight limits you may be affecting with removing the lift axles. At the plant we refer to the lift axles in front of the first drive axle as a pusher axle, and the lift axle behind the last drive axle as a tag axle.

There are federal regulations on brake timing. (Time that brakes apply and another regulation for when they release) Timing is done when there are changes made at the factory to make sure that the brakes apply and release within a certain amount of time. If you make any changes to the air system, from how it was built at the factory you could change the timing. Little changes from changing from a straight or 45⁰ fitting to a 90⁰ fitting could even change your timing. So putting a smaller house on that was originally on there can possibly affect your timing. I work in Macungie

The green needle is for primary air. The red is for secondary. The lift axle should be operating off of a solenoid. When I'm the up position the solenoid will provide air to the lift bags and when in the ride position the air will go to the ride bags. Now if you have a loss of air when I'm the up position, you'll want to check the ride bags. Then check the solenoid. Check the supply line for the solenoid which is very likely coming from a "red hat" pressure protection valve like you have in your picture. I am pretty sure the CL pooping is different than the current generation trucks as

Nick, Mack is now making a light duty truck at the RVO plant in Virginia.

I know that occasionally the coolant level sensor will go bad, if it's not the harness that Mackpro suggested, I'd try the sensor.

When the yellow button is pressed in, it puts air into the spring brake side of the brake chamber and releases the auxiliary brake. When the brake pedal is pushed in, it supplies air to the service side of the spring brake chamber and applies the service brake. I'm thinking the ch likely has either and sr7 spring brake inversion valve (bendix) or the ir2 (Wabco). (Unless you have a bridge formula semi, which only had a spring brake qrv) Ron what is yours doing wrong?

The Customer Adaptation Center is still in operation, but they do farm out some mod work to Trans Edge.

No problem at all!

If it's an electrical issue you sure have a lot of hunting to do, I'd check all your grounds, both chassis and engine grounds as well. Make sure there is no corrosion and you have good contact with the terminals.

Best way to remove it is to unscrew the four t27 torx screws from the cover and pop it out by hand.