Need help with brakes on frame off restoration

[Jerblazer72]

Everyone,
I am nearing completion of my 3 year frame off restoration project. 72 GMC LWB 4wd. I need to get brake fluid back into it and need help. I rebuilt the brakes, drained all fluid etc. Now I need to get them working. I have been reading for a couple hours and still am not sure exactly what to do. I have tried to gravity fill/bleed them and the fluid is not going out of the master cylinder. I am not really sure what to do from here. A key thing I noted from some of my reading was that the little pin on the front of the proportioning valve must me pressed in when gravity bleeding. My pin seems to be in all the way already, it does not move in or out from what I can tell. I do know that it worked correctly before I began the restoration. I was thinking of just starting at the pass rear and bleed them as normal until I get fluid down there ad proceed as normal. Any thoughts or suggestions will be greatly appreciated (especially by my wife who has to deal with me when I get frustrated like this)!

[oldspowered67C10]

You may need to bench bleed the master cylinder to get things going but before that Id try to 1 man bleed it. Get a container partially filled w/ brake fluid, attach a hose to each open bleeder(one at a time starting at the r/r) and submerge the other end in the fluid filled container and pump the pedal. You should get bubbles and then with additional pumping hopefully fluid. If that works, great, if not bench bleed.

[68gmsee]

You mention that the fluid is not getting out of the master cylinder. This could be a defective master cylinder or it wasn't bench bled properly as mentioned above.

The master cylinder has two pistons with seals and if the seals are gone it won't pump the fluid.

A good test I've done in the past is to loosen the brake lines starting at the master cylinder and have someone depress the brake pedal while you see if fluid comes out. If it does, then proceed to the prop valve. From there you can loosen the fitting at each brake cylinder to see if fluid comes out.

Things that can keep fluid from reaching the brakes are kinks on the line or internally collapsed rubber brake hoses at the front and back. They swell shut from the inside and you can't tell by looking at them.

[tubbedII]

I'm going through the exact same issue. I was hoping the master wasn't the problem, and by bench bleeding it, it seems to be fine since the fluid went up and down in the reservoir just fine. Just can't seem to get the fluid down into the lines. I tried gravity feeding (over 24 hours) and nothing. I borrowed a friend's vacuum bleeder that hooks up to a compressor to build vacuum and sucks the fluid through the bleeder. I'm hoping to give it a shot tonight.

If my friend didn't have this, I was going to try and reverse bleed it using a horse syringe and pushing fluid from the bleeder up to the master. I read that online somewhere and I guess the syringe is pretty inexpensive.

[lil hoodlum]

Originally Posted by tubbedII

I'm going through the exact same issue.

If my friend didn't have this, I was going to try and reverse bleed it using a horse syringe and pushing fluid from the bleeder up to the master. I read that online somewhere and I guess the syringe is pretty inexpensive.

I did this exact same thing for my girlfriends 1991 Chevrolet 1500. I used a turkey injector with the needle removed. Worked like a charm! I could actually hear the air bubbles escape through the master cylinder as I depressed the plunger. Bonus, I did it buy myself so no help was needed for someone to depress the break pedal, hold, and release!

Good luck!

Keith

[slikside]

subscribed.

[Jerblazer72]

OK, thanks for the comments so far. Just to give an update. Last night after posting the question I called it quits for the night. What I neglected to do was close the bleeder valve on the RR tire and the right front tire. I went out this morning to go to work and there was large pool of brake fluid below the right rear tire. The back of the MC reservoir was empty. Now I know that at least the back has fluid (and air) as it all leaked out in the night.

As far as bench bleeding the MC, I did not even know I needed to do that when I had it all apart, so it was not done. How do I do that if I end up needing to go that route? I did leave the right front bleeder open last night also and there was no fluid down in there so the front is not getting fluid. Any suggestions?

[webfoot]

It should have come with 2 plugs to thread into it. Then you put it in a vice and compress the piston in and out (I use a long flat blade screwdriver) until the bubbles stop coming out of the return holes. You can tell when you are close because it will start getting somewhat difficult to push the piston in. (it needs to be level, whatever surface you use)

[tubbedII]

Originally Posted by Jerblazer72

As far as bench bleeding the MC, I did not even know I needed to do that when I had it all apart, so it was not done. How do I do that if I end up needing to go that route?

You need a kit if it didn't come with one...they are cheap at the parts store. Like said, plug the fittings in right off the master and then you route lines back into the reservoir which should be more than half full. You just pump until no more bubbles...you can do this with the master on the truck, but only if it's level, so maybe jack the front/back up if it's installed.

Since you got the back to gravity feed, try it again back there and see if you have somewhat of pressure at the pedal when done. If so, try to do the normal 2 man brake bleed to get the fluid going through the fronts.

The only other advise I can give you is don't leave the reservoir or the bleeders open too long. I left the cap off mine and in 2 days the fluid is foggy from what I'm guessing is condensation. If not cleaned out it could lead to rusted brake lines. I'm going to clean out the master before I bleed now.