1.5 years ago I bought a parts truck 74 K10 with power disc brakes. It drove fine, I tested the brakes when I bought it anticipating swapping them to another truck. Pulled the engine and put it is another rig. The last two weekends pulled the engine out of my kids PU and put in the donor. Everything went well until we tried the test drive. No brakes, pedal to the floor. Pumped and pumped, decided the master cylinder had lost its seal during the sit and changed it out. Pumped and pumped, bleed and bleed but still cannot get a pedal.

The "BRAKE" light is staying on which indicates something is not well with the propostioning valve, correct? But if proportioning valve had slipped to front or back wouldn't I not be able to bleed the brakes? I am also assuming that the vacuum unit has a straight mechanical connection to the master cylinder, it just assists right? Thanks in advance. Patrick

It is likely that your rubber lines have deteriorated to the point that you are pulling air through them making it impossible to bleed properly.

Denny - thanks for the reply, I am going to check that, especially the back line. Based on more research here it looks like the proportioning valve may be the problem + a better bleeding job.

Anyone else??

Did you get any fluid through the bleeders? I have seen old M/C's where the bottom of the reservoir was so full of rust and sludge that the orifices wouldn't let any fluid through.

Did you bench bleed the master cylinder?

I had a project a few years ago that had sat for a few years, the rear cylinder pistons were frozen from rust/sludge. You can't tell that from bleeding, you'd have to take the drums off.

Thanks for the replys...New master cylinder and yes I bench bleed it to where I had less than 1/4" movement in the cylinder. I'm going to mess with the proportioning valve this evening, I suspect it is just a centering then getting air bubbles out issue.

sounds like a steel line has rusted thru while sitting, Rob

Update: Spent the day and 2.5 quarts of fluid and still no brakes. Checked the lines for leaks, found right front was weeping at the caliper, cleaned it up and retightened. Opening the front bleeder centered the proportioning valve so I bleed the rears until I got clean fluid from the master cylinder. Then bleed the fronts. Took for test drive, no front brakes but rears are working.

Compressed the front calipers and rebleed allowing fluid to push them out, still no pedal, as soon as I try with engine running the front circuit fails and brake light comes on. Opening front bleeder recenters proportioning valve again. Decided I must still have a air bubble in Prop. valve so break the lines to hopefully bleed off any air bubbles. Then rebleed the rears and front again. Start it up, same problem, first pump with the engine running and front circuit fails.

Am I missing something? I have put over a quart of fluid through each circuit, I can't image a bubble is still there. Tomorrow I'm going to rebleed the proportioning valve and front again. Man this is getting frustrating...