Brake light came on.

[Alzamon]

I was driving down the road and had to brake pretty hard, and the brake light in the dash came on. I tapped the pedal again and it went off. Braked again and it came back on and the pedal was creeping to the floor. So I replaced the master cylinder and no more creep but the light sitll comes on. Seems to stop the same as always, which is terrible. Maybe the proportion vale? Anyone got a part # for this or is it a junkyard only type deal? What else could cause the truck to be hard at braking? It's got a new booster on it and the pads and shoes are about a year old. Always been hard to stop. Any ideas would be greatly appreciated.

[Bob Barry]

I would check for leaks in either the front or rear system, or a blown seal at one of the cylinders or the front caliper.

The light is triggered by a pressure difference between the front and rear circuits, which is usually only caused by fluid leaking or spraying from one system.

Check the condition of the line from the proportioning valve to the rear hose; that frequently rots out as well, and it may not be leaking very evidently from a single point.

[carrotman]

On my 76, the brake line along the rear axle, on the passenger's side, rusted out and leaked. I think salt spray must sit there and rust them. Had to gently bend a straight piece as they don't sell the severely-bent original anymore. Did the driver's side too.

[AM Woody]

The proportioning valve, that is "combination valve" seems to be shrouded in black magic around here. I don't pretend to have all the answers, but I had a similar problem recently. I had to bleed it a couple times before the light went out. Did you bleed the the whole system? If not then do it. Use the pump the pedal method. I usually prefer to gravity bleed, but this apparently doesn't actuate the metering valve portion of the comination valve and it won't bleed right. Same problem with pressure bleeding. Otherwise you have to push or pull the button on your combo valve; apparently you don't have to do this if you pump the pedal. My combo valve button wouldn't move, and it didn't bleed out right until I bled it with the pedal. Your results may vary. Good luck.

Andy

[letank]

prop valve need to be reset..... brake shop job

and as for the rear brake line for the 70's, just say you have a 80's, i out a 85 in the 74.... comes pre bent, very nice $30 at the dealer

Michel