bleeding brakes!?!?!

[Rochlow]

So I'm about to blow this pig up. Everything has fought me on this truck.

69 Blazer/jimmy mix.. New booster, M/C, calipers, pads, wheels cylinders, drums, and shoes. The front brake lines are new. the rears are in good shape.

I have bled the brakes atleast five time. No air coming out of the lines after pumped and held a few times. The pedal is firm when the truck is not running. However, when I start the truck the pedal is really spongy..

Any help would be greatly apperciated..

[70cst]

I am sure you will get someone will respond shortly.

[68gmsee]

Make absolutely sure you follow directions on bench bleeding but if you have gotten all the air out of the lines, go back to the parts store and tell them the master cylinder is defective.

I had to return one of mine twice and the third one I just got my money back and went to another parts store. New parts are not like they used to be.

[Rochlow]

I bench bled the M/C in the truck. Cracked the lines and let in run in a bunch of towels.

Why would it build pressure when the truck is not running, but doesn't when it's running... I looked for and listen for a vacum leak thinking that might be the issue..

[bobs409]

New brakes will feel spongy at first, especially when replacing all of them.

Do you mean it just has a lower pedal when running? If so, I think that may be normal with power brakes.

[Rochlow]

they go to the floor with little effort. When the engine is off there is back pressure and the pedal is firm. When I start the engine it goes to the floor easily.

I am going to try and readjust the rear brakes tonight. One question I have is are the bleed screws for the front suppose to be on top or bottom?

[MARKDTN]

Make sure you bench bleed the MC thoroughly. It is sometimes hard to get all the air out, especially on the truck because it is at an angle. It is best to do it flat in a vise. Your front bleed screws should be at the top of the caliper. I like to vacuum bleed instead of pressure bleed. Finally, bleed using short clear tubing into a can of brake fluid. That way the air goes out and can't get back in again. It can be frustrating, but don't give up.

[k2rm]

I just converted both front and rear drums to disks on my '70 and had a similar problem. It was a combination of air in the lines and minor leaks in the fittings. I would find a leak, fix it, and then the system would hold a bit more pressure. But then I would find the next 'less' leaky fitting.

I also gravity bled after the pumping method wasn't getting the air out. I would open the bleeder and watch the fluid come out and look for bubbles in a clear tube draining into a cup. It took a while, but I eventually got it and have a nice firm pedal now.

[Rochlow]

Well, I switched the caliper to the correct sides and bleed fronts and readjusted the rears. It is getting better..

Any question? Does the larger portion of the m/c conatian the fluid for the front or rear brakes?
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[MARKDTN]

Originally Posted by Rochlow

Well, I switched the caliper to the correct sides and bleed fronts and readjusted the rears. It is getting better..

Any question? Does the larger portion of the m/c conatian the fluid for the front or rear brakes?
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Larger is for the front discs.

[Rochlow]

Thanks for the answer.. Yup, I got that backwards too!
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[PHAT TONY]

You need to hold the pin on the end of the prop valve in with something if you're "pedal" bleeding. I bought a few shares in the fluid industry before I got this right! However, my pedal has almost no resistance while the engine runs but locks the brakes up quick and hard, my booster's out of a '91....

[sneaky]

my wife and i bled mine sat nite, took maybe 15 mins....do it with the truck on. i only had to do the pass frt and the driver frt...i have discs...there is a dummy lite on the dash too that will let you know its good...should go out when you got it. i just put a vacuum line on the nipple and ran it into a bottle halfway full of brake fluid....crack open the valve, have your pedal person push down....then while its still down close the valve have them go back up....then open, have them push (you'll feel the air leaving) then close and up...repeat til just fluid. usually youre suppose to start from the pass rear then driver rear then pass frt then driver frt...i tore the driver frt line when doing my drop coils (ouch btw it hurts when the whole assy drops on your leg,lol) anyways, good luck.

[lil hoodlum]

I hear you! I know how frustrating it can be to bleed the brake system.

When I first bought my truck, the PO told me the truck had "standup-brakes." Literally meaning the driver had to standup on the brake peddle to get the truck to stop. Even then it didn't really come to a stop. It just kept rolling forward a few inches at a time. Talk about scary. So my first project on the truck was to rebuild the brakes. I replaced everypart one at a time. Every little thing helped a little more than the last one, but, it would not still stop. Finally the last thing to do was the master cylinder. After I bench bled it and installed it I finally had brakes!!

On my girlfriends 1991 chevy pu with hydralic clutch we had a real hard time bleeding that sucker. I mean I tried everying in the book. What finally worked for me was I took a turkey injector (i.e., a really big syringe) and installed a clear hose onto it and I pumped brake fluid up from underneath to the clutch master cylinder. It was easy and I did it by myself! No one to hold down the clutch pedal. It did force the air trapped in the line and brake fluid out of the clutch master cylinder. So be ready to "catch" the spillage from the master cylinder.

Good luck!

Keith

[zeeklu]

Make sure the back brakes are adjusted right . If they are not adjusted right it will give you a low pedal. Chris

[Rochlow]

Would a bad proportioning valve create this problem. It's the only thing I haven't changed. Plus, the pin the front of it I can't seem to push in

[jocko]

pedal dropping once truck is started (i.e. vac signal to the booster) could be a sign your power booster is bad/diaphragm torn internally. is it new as well? Still seems that is the main clue - that you have a solid pedal when engine not running and no not when it is - only diff between those two states is vac signal to the booster. Most of the problems alluded to above - and they are all valid problems and things that happen - would mostly seem to occur whether or not the truck is running. i.e. an open line or big air bub will compress regardless of engine vac signal, won't it? (and I'm not sure what the answer to that question is...)

[Rochlow]

After talking to a friend that's been a mechanic for awhile, he thought that it sounded like a vacuum issue also. I've looked for leaks but haven't found any. This has really got me stumped!

I think I might return the m/c and booster to see if they are faulty. After that it's pay someone who has more knowledge than me to fix them(which I hate to do!)

Thanks guys for all the help! It's what makes this site so great!
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[hatred]

When I had my 67 I would put a clear tube on the bleeder then put that into a clear jar full of brake fluid. Just pump until no air comes out. It will push the air out and suck fluid back in. Never had a problem with them after doing it this way.

[Rochlow]

So I've bleed these brakes about 20 times. I'm only getting air out of the rear and there are no leak!

So I think the master cylinder is bad? That the only place I can see that would suck in the amount of air I'm getting out
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[68gmsee]

As I mentioned in my original post.... I had to take mine back twice and got my money back on the third failure. Went to another store and got a different brand, bench bled it exactly to directions and never had another problem.

Don't know if anyone mentioned, but when you have a booster getting a solid pedal without the engine running is normal. I always adjust my power brakes with the engine running.

Hope that solves your issues.

[fastwillie 696969]

im wondering if the right push rod is used on the new booster > just sayin"

[LostMy65]

Was this ever resolved?
Did you ever figure out the issue?
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