Brakes are kill'n me

[marco chevy]

I just recently became a member after being referred to this site by my Cousin. Best thing I ever did. I'm working on finishing my 69 C-10 lwb from the frame up. Everything looks great and works awesome accept the four wheel drums. I've replaced all brakes with new brake kits, brake lines, rubber lines, and the master cylinder. The problem is that the brake pedal goes to the floor and the brakes work a little when the truck is running. When I plug the vacuum line that goes from the booster to the manifold they stiffen up but still work a littler. I've bled the entire system many times and still can't get he darn things to keep steady pressure. I also adjusted the shaft that goes into the master cylinder in and out with no noticeable difference. Do you guys think the booster may be bad? Thanks for any help.

[68gmsee]

If you're absolutely sure there is no air in the brake system then the master cylinder could be the problem. There's a primary and a secondary piston and even on new ones the internal seals can leak. Just make sure there aren't any cracks or loose connections on the brake lines, cylinders and rubber brake hoses.

Bench bleeding of the master cylinder is an important part of the job so insure that's done correctly according to the instructions.

If you want to isolate further, you can temporarily convert it to non power brakes if you have the pedal to master cylinder linkage for non power brakes. I did that on my 68 GMC when my booster went bad on me.

I just removed the m.c. and moved it forward, removed the booster and bracket, bolted the master cylinder up and installed the original link.

[cdowns]

are the brake shoes adjusted properly? they should b adjusted out to where there is a very slight rubbing sound if you spin a wheel

[Longhorn Man]

Pump the pedal up and hold it. If the pedal stays firm and doesn't drift down, then you need to adjust the shoes up.
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[68gmsee]

Just to clarify... You indicate that by plugging the vacuum line to the booster the brakes stiffen up. Does the pedal drift down slowly or goes all the way down right away?

[marco chevy]

Thanks 68gmsee. I will try the non power brake trick if replacing the master cylinder again doesn't work.

[marco chevy]

Hey longhorn man does pumping and holding need to be done while the vehicle is running? I assume so, but just want to make sure.. Thanks

[marco chevy]

The pedal is more stiff but it still goes down all the way. No real slow drift or anything like that. The brakes still respond the same. They only slightly work when the pedal nears the bottom.

[marco chevy]

Does anyone know for certain the length of the push rod that the booster forces into the master cylinder. IT has that little adjustable nut and threads that I've been screwing in and out to no avail.

[americanmusc1e]

more than likely you have an air bubble near the master cylinder or the adjustment is out on the drums....

here is the easiest way ever to bleed your brakes..... you need a couple feet of clear hose that will fit over your bleeder screws and one of these from harbor freight http://www.harborfreight.com/8-oz-hi...ler-66350.html

Make sure that the master cylinder is almost empty....fill the oiler with brake fluid and attach the hose between the oiler and the bleeder screw..... open the bleeder and start pumping brake fluid up from the bleeder to the master cylinder until no air bubbles come out of the master cylinder....do this for all the bleeder screws... works every time.... even on stubborn clutch hydraulics....

[68gmsee]

Originally Posted by marco chevy

The pedal is more stiff but it still goes down all the way. No real slow drift or anything like that. The brakes still respond the same. They only slightly work when the pedal nears the bottom.

Okay. The stiffer pedal is normal but if it goes down and doesn't pump up make sure the brakes are adjusted as cdowns and longhorn man mentioned above as the next step.

If they're adjusted properly and everything else looks good, then the master cylinder is still the primary suspect.

I don't know what the length of the link is supposed to be since I'm sure all vehicles are going to be different, however, if you have extended it and it doesn't help that's not your problem.

[Longhorn Man]

pumping the pedal with the engine on will make it easier. Doing it with the engine off will make it easier to tell if it is pupming up.
Either way won't matter in all reality.
As for the pushrod length, with the engine off, press the brake pedal a few times will the pedal is hard. Now get out, and lean down and press the pedal by hand with light breassure. You want about a 1/2 inch to an inch of free travel in the pedal.