Mike, did your brake warning light on the dash also come on when you discovered this problem ? I had a 77 F-350 Dually with the old school double chambered master cylinder and I had a leak where one of the lines screwed into side of the master cylinder, and I had the master cylinder replaced. So check your master cylinder and also the lines going from the master cylinder to the proportioning valve, and I reiterate PLEASE DON'T DRIVE THAT TRUCK while you have brake issues, or you'll have NO brakes after you pump out all your brake fluid through the leaking brake line.
Sadly, the brake light on 8 gen truck don't come on until it's too late. You loose pedal pressure first, then it makes a mess under the truck, then the light comes on
The same light tells you that the parking brake is on
Hey guys! Apologies for the late reply. Had a professional do it, replaced the line and a cylinder was bad on the rear side. Not comfortable to tackle a break project yet haha.
The brake warning light never came on. In the few daysit sat I just kept up the fluid level with some fresh DOT 3 and put plenty of newspaper under the truck. Thank you all so much for the help, I dont know what I would do without you guys