On my 94 Ranger, yesterday I took my wife to the dog groomers to pick up the dogs, she went in I left the truck running, keeping my foot on the brake pedal. All fine and well, until about 10 mins of idling. Brake pedal sank all the way to the floor and truck started rolling, slammed on the e brake, pumped the pedal a few times and finally got the brakes back. The brakes work excellent, except for the above stated incident. Will slide the tires, and throw you into the dash. It has never done this to me before, plenty of idling and holding the brakes.

So today, I drove the truck around to get it warmed up, came home hooked up vacuum gauge to engine to see if power booster was leaking down, all ok, 22" of vaccum at idle, hit the brakes vacuum goes to 19" and stays there, held pedal for about 15 mins, the brakes went to the floor again. Crawled under truck no fluid leaks, master cylinder resivoir full, fluid is a little old, 3 years since I completely overhauled brake system.


So any suggestions? Master Cylinder crapping out? Contaminated fluid? Please give me some input, cash is kinda tight and I want to go in the right direction!!!

Note all brake components (except, power booster and master cylinder)only have about 15k miles on them, I dont drive the truck much. All new calipers, wheel cylinders, rubber lines, springs, pads, etc have been replaced. The master cylinder and booster have 130k on them.

Thanks

 

sounds like a internal leak in the master cyl. or air has entered the system.

 

^ + 1 on the master cyl.

 

I can't think of anything but the master cyl. Who knows when that could happen again, maybe in a panic stop. I wouldn't F around just replace it.

 

Thanks for the input master cylinder ordered!!