Brake Queston

[tomford]

So i got my truck together, and drove it and then i had no brakes. The pedal would go to the floor, running or nor, no visable leaks. So everyone said master cyl. i just replaced it, bench beld the master and bled it at the fittings on the master. I can pump the brakes up with the truck not running, and get a good soild non faiding pedal. as soon as i start it it goes right to the floor. What could it be, my buddy says it could be the booster, right behind the master. What do you guys think?

Thanks
Tom

 

[chevyuser74]

which truck? and what is the setup stock? or did u switch to disc, otherwise u could still have air in the lines, i highly doubt its goin to be the booster though.

 

[tomford]

81 chevy, d44 front disc and corp 14bff drum rear, as far as i can tell stock setup

Tom

 

[tomford]

But the pedal only goes to the floor when its running

Tom

 

[planedr]

Wow, mine started to do the same thing today when I was driving it. But only occasionally. like at stop lights, it would go to the floor but the truck wouldn't move.

 

[tomford]

yea, last time i drove it it moved when it was at the floor. It apeared to be leaking from the back of the master, the boster was wet where the master sits, Not soaking wet, but damp

Tom

 

[chevyuser74]

the one that does it sometimes would be the master, now yours going to the floor when the truck is running i would start by bleeding all the wheels (this wont cost u anything but fluid), see if your rears are leaking from the wheel cylinders, i work at a shop (not claiming to be all knowing but we've never replaced a booster for this problem the 3 years i've been there) is your brake light on?
or heres what u do pinch off your hoses with vise grips (just lightly enough to close the hose, not to cut it, use common sense this practice alot of people dont like but ive never had a problem doing this) start the truck press the pedal if it goes to the floor bleed the lines, if not have another person take off the vice grips one by one seeing how far the pedal goes down each time one is released, the one that goes down is your problem start by bleeding it, other wiise u might have to replace something

 

[dremu]

When the boosters fail, you have a hard pedal all the time. See, the booster provides power assist to the pedal movement, so when they fail, you get LESS assist, i.e. it's hard to press.

If the pedal goes all the way down you have a brake hydraulic issue, i.e. master cylinder, caliper, wheel cylinder, or hose. Or it needs to be bled more.

-- A

 

[4X4HIGH]

Sounds like a bad master cylinder to me, especially since you said it's leaking at the rear next to the booster. I would also suggest that you make sure the rear shoes are adjusted up properly. The rear shoes not being adjusted properly can cause the wheel cylinders to move much further than they should and end up getting into a portion that may have rust and tear the rubber lip seal within the cylinder and cause a leaking wheel cylinder. Also if you still have your e-brake hooked up it will also affect how well your e-brake works.

 

[tomford]

i just replaced the master, and before i replaced it it went to the floor all the time, running or not, not it goes to the floor when running and you get a normal pedal after pumping it not running

 

[Leper]

Park the truck on a flat surface and let all 4 wheels gravity bleed for half an hour. Then bleed the brakes the regular way. I believe you have air in the lines somewhere. Your old MC could have let the air in. I would never replace the MC without doing a full system bleed afterwards. Brake fluid, by nature, absorbs moisture. When it gets old, it can give the spongy feel you are having. It can also get contaminated enough to destroy brake components. If you have taken the drums off and see no fluid, and you know for a fact the calipers are moving freely, and you have checked every connection for leaks, the only 2 options left are a bad, new, MC or contaminated fluid.

I would bet money on the fluid. Or a line not tight at the MC

You havent replaced any lines recently, have you?(hard or flexible)?

 

[Mike D]

IMO You still have air in the line. Get a friend and bleed all the wheels from the closest to the master cylinder to the farthest using the bleeder valves. Then reverse the bleeding order. If one of the bleeders is frozen or broken off fix it or replace that wheel cylinder/ caliper. That is the culprit. Also adjust the rear brakes out for correct performance.

 

[chevyridinhigh79]

i have the same problem. iirc there should be a rubber seal in between the power booster and the master. if theres fluid in your booster you need to get a new one. i bled the brakes on mine and even though i have a bad master it still feels much better and i have a harder pedal now

 

[Leper]

IMO You still have air in the line. Get a friend and bleed all the wheels from the closest to the master cylinder to the farthest using the bleeder valves. Then reverse the bleeding order. If one of the bleeders is frozen or broken off fix it or replace that wheel cylinder/ caliper. That is the culprit. Also adjust the rear brakes out for correct performance.

I always start with the farthest away.