I was driving this morning and came up to a stop and the brake pedal went all squishy and sank to the floor, had to use the emergency brake to get home. The brake light and the ABS light is on now. When I got it home I took a look and noticed a little brake fluid that had spun up into the rear wheel well - don't see any busted lines running to the rear brakes though & the lines look fine up to the point where it goes into the brake. Anybody know what the most likely culprit would be inside the rear brake (rear drum 4 wheel anti-lock). Also 1 section of the master cylinder is empty now (because it all leaked out somewhere in that rear brake). I've worked on the front disc brakes before and it was all fairly straight forward, but never messed with the rears. I had a brake shop replace the rear drums, shoes, wheel cylinders etc. about 2 years ago and thought everything was good for a while back there. Any help at all appreciated.

 

My guess would be a line is rusted out, a hose broke, or a wheel cylinder is shot and leaking.

Im not sure if there is anything else back there that could leak. Jack it up and set it on some stands and pull the wheels and drums off. Im sure it will be pretty obvious once you're under there.

Have a good one. Hope this helps.

 

Probably rotted the line behind the fuel tank like I did.
Get yourself a motorcycle jack from sears or something and use that to lower the tank. theres two hangers with a nut on one side and a slot on the other. disconnecting the lines from the tank is a bit tricky, youll need to squeeze up there and look with a mirror. You can decide whether you want to do this with fuel in the tank, or use a transfer pump to move it to some jerrycans.
once you have the tank off its a good idea to check the fuel sender and the mesh filter.
Id buy two chevy one-ton wheel cylinders (dont fool yourself thinking the bleed screws are gonna come off) from an auto parts place (part #'s on this forum someplace) and a bunch of brake line (two 6' sections) and a bunch of spare connectors and unions. Good time to flush the system with fresh fluid too.
Its not a difficult job its just a PITA.
Oh yeah.. put grease on those bleed screws for the next guy.

 

You're exactly right - rotted line behind the fuel tank! I had spotted the fluid that hit the rear tire when the line blew and just assumed it was coming from inside the brake. I'm going to try to replace the bad section without dropping the tank (kinda wish I hadn't filled up before starting out yesterday) it looks like everything from the front, back to where the frame bends down behind the cab is okay - no rust anyway. I think if I can pre-assemble an 8' section (I'm assuming Autozone only has 6' pieces) I can just thread it through the frame rail, it looks like I can just reach the fitting at the other end if I drop the spare tire down. I'll paint the new line section with some rust inhibitive paint like I did with the fuel lines - might help them last a little longer.