Lost power brakes and brake warning light on...need some assistance.

[05crewcab]

Hi guys,

Over the last month or so every so often i would apply the brakes and have a squishy pedal...no power assist. Yesterday, the brake warning light came on on the dash, but the power assist was still there. Today, the light was still on and I have NO power assist...damn.

I tried to bleed the brakes to see if air was the culprit. Started with the rears and they bled fine...moved to the front passenger side and bled out about 4-5oz's of fluid then it just started pumping air, large amounts of air. moved to the driver's side and same deal. I believe I bled them the right way. I don't see any leaks or wetness or kinked lines anywhere, and the rear did not do this...

At this point I started reading here and decided to try and reset the prop. valve thinking that it was stuck blocking the front lines. I first pulled the warning light switch and checked out the hole. looks like at the bottom of the hole there is a pin or rod (which I presume touches the switch and causes the light to turn on). Anyway, I tried to reset the prop. valve and that pin is still in place. Normal? I put the switch back in and topped off the master cylinder. Then cranked the truck up and the light still came on with no assist. What gives?

Is my master cylinder kaput? Prop. valve extinct? Would the brake booster cause all this? (These are all factory parts) The air in the front lines is troubling me the most...


I'm stumped...any suggestions?

[cdowns]

bad master cylinder is probablly the problem

[68gmsee]

Yes. Replace the master cylinder. Keep the receipt, cause they don't last like they used to. Be sure and do a bench bleed.

Since you're going to have it disconnected and if the three rubber lines are original, might as well replace those also. If they're not bad now they will be sooner or later.

[05crewcab]

Thanks for the input guys. Any recommendation on where to get the brake lines? I looked at oreilly and they only have the rear line...

[68gmsee]

I got mine at auto zone.

[05crewcab]

Thanks. I was looking at the master cylinder numbers from ACDelco and it looks like the MC is used up until 1980 on the 3/4 tons so I will check and see if maybe lines from those model years will work...seems like that would be the case since the whole front subframe is interchangeable.

[05crewcab]

Pulled the MC tonight and have a question. The short brake line to the Combo Valve from the rear reservoir in the MC is smaller in diameter than the front line. (pics) I would think that the front brakes would need more volume hence a larger diameter tube?? Just wondering if I need to re-do these lines while things are apart, and what is the diameter supposed to be?

[wilbilt]

Is that orange silicone sealant around the top of the MC? Why?

[05crewcab]

The gasket leaked and that orange gasket maker was an ill fated attempt to seal it up better...

[05crewcab]

It was the master cylinder...$45 bucks and an hour later I have power brakes again Thanks guys.