Brake Problems Again!

[meyerk]

I just replace my Master Cylinder in my 86 GWag. and my front brakes work fine but my rear brakes don't even work. I don't know that they ever worked since I bought it. Any ideas or hints would be appreciated. Thank You

[andy d]

i wonder if the proportioning valve clamped down because the rear brake line is leaking.

[Treeshark]

Could need to do some more bleeding. The rears can be a pain with the proportioning valve release button. Depending on the year, you've gotta have it either pushed or pulled to get pressure to the rears while bleeding. The button is on the front of the valve which is located on the frame under the driver's side of the vehicle directly below the master cylinder. Hope this helps.

[AM Woody]

If it's the combination valve doing that, then it would turn the brake warning light on. I'm assuming it's not on. Is the bulb good - i.e. does it it light when you turn the key on?

Have you even bled it? If you have, are you getting anything at the rears? Probably just needs (more) bleeding. If you bleed pump the pedal method, you shouldn't have to push/pull the button on the combo valve.

I've also had rear wheel cylinders sieze before on a 10-year old car. If they never worked you may need wheel cylinders.

[meyerk]

The Brake light comes on and always has but i figured it was the parking brake that was stuck when i got it until I disconnected it. But when I do try to bleed it I don't get anything not even air bubbles. Could you tell me more about this Combonation Valve, would it be on the '86 Grand Wagoneer?

[andy d]

did you bench bleed the new m/c? are all the fittings tight? if they arent, then they will suck in air and it will never bleed. the 86 definitely has a valve.

[meyerk]

I bled my m/c and all the fittings are tight.

[carrotman]

Have someone push the brakes while you open the bleeder on both rear brakes. If fluid comes out both sides there must be a cylinder leak or something mechanically wrong. You should pull the drums and check it out. If no fluid, somethings wrong with M/C.

[driftpin]

Mine did the same as yours, prop valve went south.

[AM Woody]

I agree it's the combination valve. Follow the brake lines from the MC down to the frame rail and there it is. Has 5(?) brake lines and a wire going in/out of it.

It might be shot since it's been that way for a while. Question is can you get it working? I heard tapping on it can help get it unstuck. I would also try to push/pull the button/pin on the front of it. And keep trying to bleed - pedal method - and maybe it'll start working. I did all the above and mine is working okay now.

[carrotman]

According to the 76 TSM, the combination valve consists of three parts. 1. The metering valve holds off (delays) full hydraulic fluid pressure to the front brakes until the rear linings make contact with the drums. 2. The warning light is activated when a hydraulic pressure loss occurs in either the front or rear brake systems. 3. The proportioner section provides balanced front-to-rear braking during high pedal pressure stops. The proportioner does not operate during light pedal pressure.

If meyerk's brake warning light is on, there must be a leak, probably in the rear. I don't know about the 86, but for bleeding a 76, the metering section must be held open using the easy to make J-tool. If the problem is in the the valve, it isn't repairable.