Brake problems

[Wharf Rat]

I have a 1970 C-20 with front and rear drums and I am having some problems.

The truck would stop fine but you had to stand on the brake pedal to get the thing to stop. So I changed the master cylinder and now I have almost no brakes. I have bled the master cyl 3 times and the brakes about 5 times and nothing has changed. The idiot light light comes on now when you step on the brake pedal, too.

Any ideas?

[sneakysnake]

You still have trapped air in your system, but it sounds like you may have other problems as well.If you had a good pedal but just wasnt stopping well is more of an indication of worn or glazed shoes or leaking wheel cylinders.

[Longhorn Man]

You say the pedal is hard....is it hard like when the engine is off and no vacume in the booster?

[70GMC_BOB]

I just had my brakes fixed on my 72 c20. I had hard pedal and leaky master cylinder. So I installed a new master cylinder and had a soft pedal and no brakes. when i bled the rear brakes the pedal would not go all the way to the floor. I then discovered leaky looking rear hose(the one on the axle). I am currently moving so with the new hose in hand took it to the shop to install and bleed brakes. I believe the hose was blocked inside. Now they are correct. this was just my experience. good luck!

[Brainchild]

Did you bench bleed the master before you put it on?

[70GMC_BOB]

If you didn't, I bled the booster on the truck with the kit using short pedal pushing so I didn't have to play with a wooden dowl! worked great

[86SILVERADO]

Well, I can tell you that on the 67 I had the exact same problem. My shoes were not worn. I finally figured out that they were not self adjusting ( with hard braking in reverse) and I manually adjusted them and now they are fine. Try jacking up a wheel, use a friend or a 2' piece or so of 2x4 to hold the brake pedal to the floor and go out and see if you can still spin the wheel, you most likely will find you still can spin it somewhat. You just have to pull the little plug at the bottom of the backing plate keep turning the wheel upwards with the end of a screwdriver blade until you cannot spin the brake drum at all by hand with the pedal to the floor. You will also have to bleed the whole system first as stated but my guess is your real problem was with the shoes not adjusting or they could also be worn down too much.

[Wharf Rat]

It isn't hard anymore. It actually feels fine, but there just isn't any brakes there when you press the pedal.

When I was bleeding them the rears would go to the floor but the fronts didn't. Sounds kinda like what happened to 70GMC_BOB?

I did bench bleed the master cyl before I put it on the truck. I actually did it 2 more times on the truck when nothing was working.

What is the idiot light telling me? What is triggering that?

[70GMC_BOB]

I have been told it is a pressure diff switch. i think if the front or rear have low or high pressure(not equal) it would come on.

[blazerparts]

Those self adjusters are kinda tricky. I always take the time to clean/oil them while doing the brakes. Wanna make sure they are put back in the right position (yes, I've put them in backwards). Adjust them so shoes are just draggin on drum, then back off half a turn. Check again after bleeding. Then a couple hard stops while backing..........bada bing, bada boom.

[Wharf Rat]

Yup, it was the self adjusters not adjusting and a little more air in the line. Stops on a dime now. Thanks guys.

[Longhorn Man]

Blazer parts...try antiseixe compound instead of oil on the self adjuster threrads. Works much better and lasts longer.
These should also be avalible at the parts stores...and it is a good idea to replace them and the hardware that holds it all to the backing plate when ever you put new shoes on.

[CHEVIBUBBA]

[QUOTE=What is the idiot light telling me? What is triggering that?[/QUOTE]
is the light staying on?
the proportioning valve also doubles as an isolation valve.
when pressure is on one side & not on the other the valve inside shuttles over & cuts the "no pressure" side off.when it does it also trips the switch
sometimes it can get stuck.to reset this you'll need to stomp the brake pedal.
make sure you have no air in the line between the m/c & prop valve.
if that doesn't work you may need to disassemble it & manually reset it/replace it.