Yesterday, my brakes went on vacation. They can be reached, though-- but not easily. On first application, the pedal goes all the way to the floor. Pump it two or three times & they work adequately, which is quite a change from the day before yesterday when all seemed to be well. Fluid level was about an inch down in the rear portion of the reservoir, which I brought up to about 1/2" right after this started. Whaddya think? I'm thinking maybe the 90w that has been leaking out of the hub finally rotted the rubber parts in the wheel cylinder, but I haven't checked for signs of fluid leakage because it's so flippin' muddy around here. Oh, and truck has 225K on it. Thanks!
- Chris

 

Sounds like you have air in the system.

 

That occurred to me, but I haven't touched the brakes on this truck, and <<POOF>> air gets in? Any ideas on that one? Thanks for the reply, G.
- Chris

 

fluid leaking past the piston in the master cylinder.

 

I'd say you have about a 95% chance that the master cylinder is shot. I've had the same thing happen on several different vehicles, and each time it was the master cylinder. Check your booster to make sure the vacuum diaphram isn't shot - brake fluid leaking into the booster can kill the rubber diaphram.

 

The fluid in the rear section of the master drops as the pads wear. Normal and natural, I do not recommend topping that off since it just gets pushed out when you change the pads. I do agree that it sounds like a master cylinder problem. If a new master doesn't cure it, then it's the ABS dump valve.

 

Like Wanna said, replace the Master Cylinder and if it doesn't change at all it's the Hydraulic (dump) Valve. My truck did what you described, and it was the dump valve. Got a new one at NAPA. It's in the frame rail toward the rear of the truck.

 

I just has a similiar problem. One day my truck started veering to one side whenI applied the brakes. Also, if applied to hard they would lock up because the drums would get hot and stick. I checked the master cylinder and all of the fluid for the rear was gone. Since brake fluid doesn't evaporate and I just put new brakes on all around, it ended up being the wheel cylinder. Replaced them and now she stops fine...just another option...

 

Just changed the seal on the right rear wheel & the wheel cylinder appeared fine; no leaks (FWIW- a Mercury boat propeller makes a great seal driver... ), so that's probably not it. As I drove in the driveway tonight (& almost through the garage door), something made me think it was the master cylinder, also. Thanks for all the help, every one.

So what's a dump valve cost? My checkbook's kinda all dumped out...
- Chris