Hey fellow CAD family. I have not posted in awhile glad to see alot more new family members joined. Ok my situation is when I push my brake pedal in I here air hissing behind the dash. Any suggestions? Truck is 2001 Freightliner FLD120 ex Covenant truck. Please give all sugesstions. Thanks your CAD relative Collard Greens.

It probably isn't behind the dash, but on the firewall.

Pop open the hood(without engine running) push in pedal, and have a friend check all the air lines on the firewall.

It also helps to have a spray bottle with soapy water.

Thanks allan5oh will try that.

You'll probably just need to push in the air lines back into the quick connects at the firewall. Push in the biggest ones first as those go to the brakes. Should be simple.

Quick connects usually wear out, and you have to replace the whole quick connect, and cut the air line so you have a fresh line going in.

I've been dealing with this for a while with my truck.

Thanks for the help. I will look at i when I leave the office today.

air leaks can be tricky. i heard air pouring out behind the park brake valve in dash. so i replaced it. air was still leaking. found out it was an air line under truck had rubbedd a good size hole. the sound i was hearing was air being supplied to replace air being lost not a leak in valve.

Sounds like you might have a leak in your brake service line (blue hose) from your tractor to your trailer. When apply the brakes you hear the air going through the valve and out the leak so it sounds like it's in the cab.

Or like heavyhaulerss suggested under the truck.

I opened the hood and sprayed some soapy water on the contraption on the firewall where all the airlines go into. I had to press the brakes myself you know how it can be when you ask another driver out here. But I seen some water squirt away. I'm going to put some liquid soap on the fittings that when I press it I can have some bubbles. Thanks for the assistance. I put new hose red and blue on the tractor.