ratzen fratzen brakes!

[speesh]

I have a 71 c10 burb, with power brakes. I have replaced the master cylinder. The brake light comes on if I push on the brakes hard but if I use them gently it doesnt. When I am pushing on the pedal, it feels like it is working, but if I give a little more pressure it goes down about an inch more and the light comes on. The brakes always work though. I bled the brakes this weekend and now it is worse than before! It feels like the brakes are working ok, but maybe not the booster? Can someone tell me how to bleed them correctly? or any other ideas ? I have always had problems with brakes on these trucks, is it just me?
Oh yeah, am I supposed to adjust the rear drums? or is it automatic?

[Blue4x4]

I have found that the Auto bleeder sold at harbor freight works well. You might want to bleed the rears also. The fitting looks like a grease fitting. Good luck

[VTKidder]

I've always bled brakes with 2 people; never used a one man bleeder setup. Have someone running the pedal and one on the bleeders. I start at the farthest corner from the booster (passengers rear), then worked up to the front drivers wheel. Have your friend pump the brakes 3 times (engine off), then stand on that damn pedal. Have them holler at you "ON!" or something so you know they're standing on it, then just loosen the bleeder. Fluid comes out (hopefully air too), and when it's done flowing, close the bleeder. Make sure your friend doesn't release the pedal until you've closed the bleeder. Do this to the passengers rear, then drivers rear, then passengers front, then drivers front. MAKE SURE YOU CHECK THE FLUID RESERVIOR LEVEL BEFORE AND AFTER EACH INDIVIDUAL BLEED!! If you're bleeding down low, but suck all the fluid into the master cylinder and start sucking air, you're doing no good at all. Probably making things worse. As far as adjusting drum brakes, it isn't automatic. There should be a threaded setup you can see through the dust cover with teeth on it you turn with screwdriver that pushes the bottom of the shoes further apart (closer to the surface of the drum). Best of luck.

[Zeus]

You better double check the bleeding order. I always thought you bleed from the closest to the farthest.

[68LSS1]

Farthest to closest is correct.

Edit: Also after bleeding the brakes again and you are sure all the air is out, stand on the brake pedal. If it slowly goes down and then stops before bottoming out you still have air. If it bottoms out then your master cylinder is leaking internally (I've gotten more than one remanufactured mc that is bad out of the box). Make sure you bench bleed them before installing.

[PanelDeland]

You should pull your drums and take the adjusters out.You can free the adjusters up then lube them well.They may work for a while but after 20 years of owningm one of these trucks I have never gotten a set of auto adjusters to work for the life of a set of shoes.

[JayDubBlazer]

Bench bleed?

[Southpa]

Hmmmm, I had to log in for this one.

If your brake light is coming on I would suspect the proportioning valve is a little off and needs some adjusting. Never done it myself but others here can advise you on that one.

For rear drums I usually adjust them myself. Rear end jacked up, wheels on and tighten the ratchet pawl (little toothed wheel) until you get one full revolution before friction makes it stop. The self adjusters might work if the workings are lubed with "Never-seize" or some other graphite lubricant. But I never trust 'em.

[Blue68]

The prop valve trips when there is an unequal pressure between the front and rear ciruits. Most likely, you have air in one of the circuits, and possibly both. It may also be a bulging hose. As you apply more pressure, it would bulge more where the other circuit won't thus putting more pressure on the sound circuit and pushing the piston in the proportioning valve one way or the other.

[ddsmith]

Bench bleed?

This means to put fluid in the master cylinder and mount it in a vise or suitable substitute. Run short sections of brake tubing from the master cylinder outlets back up to the reservoirs and push the piston in the force fluid to flow through the outlet ports and into the reservoirs. When the fluid runs air free then the bench bleed is complete. This will ensure air is out of the master cylinder and as long as you don't allow the reservoirs to go empty will rule out this as one of the sources of problem when bleeding the brakes.

[speesh]

Thanks, everyone, for all your posts. Now can someone please explain to me how to "adjust the proportioning valve" ? I know it has something to do with the little red button on the end...........

[Blue68]

There is no 'adjustment' available. It is either tripped or not. I have heard of resetting when it trips. The circuits require equal pressure on both sides of a valve. If one side drops a piston slides to that side shutting off pressure and triggering the light, which is the switch in the middle, right above the piston. It can be reset by getting the pressure up to snuff on the low side and cracking a bleeder on the high side to push it back. Sometimes, they will 'stick' and require replacement instead of being able to reset.

[FrankHoy]

You are suppose to be able to set the rear brakes by driving in reverse (10-15 mph) and pressing the brake firmly. You may need to do this a few times. This works, provided the star adjuster is not froze/rusted.
I would suspect your problem is with not being bench bled properly. Follow DDSmith's instructions.

[my new 72]

I just finished replacing my whole brake system except the prop valve and had to reset it. Here is how I did it. I got a large c-clamp and clamped it onto the prop valve so it held pressure on the pin and allowed the rear lines to flow. I them bled the rears. After the rears were bled I took the clamp off and bled the fronts. After that they work great. they even lock up the big ass 255/55/18 rubbers. Try it and I'm pretty sure your problem will be solved.