VERY bizarre brake problem

[rccardude04]

Okay! pumped new fluid into ALL FOUR TIRES from the electric pump. Loosened hoses from M/C, pushed pedal down, fluid came out. yay. Still does a similar thing but it kinda almost seems to workish. My buddy has a vacuum pump that we're going to use on Saturday (which stinks but that's how long it takes to order hoses and the only time he can help us).
-Eric

[5.0zone]

I've known this to happen on two GM cars and both times it was the rubber brake line to the caliper. The rubber would breakdown inside and act like a check valve. You might try taking it off and inspecting the inside if you can get enough light in there to see.

[rccardude04]

You're like the 8th person to say hose, so I finally broke down and got one. O'reilly actually had one! $24.99 though so I hope it works. We're going to change it tonight. I'll keep you guys posted. Thanks again for all the help and advice!!
-Eric

[rccardude04]

Hose didn't fix it. We now know why it won't work though. When you press the pedal to bleed it, and then release the pedal, the thing WILL NOT suck fluid back into the M/C from the reservoir. It's just not doing it. I don't want to go through how we verified this, but that's what is happening. It sucks it in fine for the RF/LR wheels but not the LF/RR. Any other ideas?? Even simple crap that we shouldn't have overlooked? I'm open to anything now. It's getting annoying.
-Eric

[mechanicaldj]

first of all
you bled the brakes in wrong order in the first place

you start with the right rear then the left rear, right front and last the left front (longest line first, shortest line last)

[rccardude04]

We tried to do the right rear first a couple of times. It doesn't matter. It still won't pull fluid into the reservoir. We had thought about that. Thanks though. Good suggestion
-Eric
--Edit: Will it really make that big of a difference bleeding the left front first? Because I guess we didn't try it properly recently. Just when it started doing it first.

[snag]

Oh no

I just got done replacing the LR brake line and installed a new MC and I have the same thing happening. No fluid coming out of the RR tire. I figured I got some crap in the line replacing it. But now I'm leaning towards MC bleeding. Does it make a difference in stroke if I bleed it on the car vs on the bench?

[mattswabb]

Re: Oh no

Does it make a difference in stroke if I bleed it on the car vs on the bench?

I've always done it in the car.

[rccardude04]

Okay, when we were bench bleeding it last time, I tried putting my fingers over the ends of the PVC tubes they give you, and it wouldn't pull fluid into the MC from the reservoir. It just collapsed the PVC tubes instead. Is this a sign? Should I try pinching the lines right by the ports?
-Eric

[rccardude04]

JUST tried an experiment...
I took the front line off since that's the one we're having trouble with.
Assistant pushed the pedal down and a little fluid squirted out.
I plugged the hole with a plug thingy that came with the bleeder kit.
He released the pedal.
I waited ~10 seconds, and pulled the plug off. Sure enough, I heard this PSST noise as air got sucked in.
I repeated this a couple times and it seemed to push fluid each time. The longer I waited between the release of pedal and release of plug, the less air seemed to want to be pulled in. Is it normal for the master cylinder to draw fluid in very slow from the reservoir??
-Eric

[mechanicaldj]

fluid is supposed to go both ways

pressure out to the wheels(applying brakes)

and return (releasing of the brakes)

when you bleed the master cylinder (bench or in the car)
you keep pressing the plunger slowly , in and release, until no air is be expelled from the tubes from the ports back into the master cylinder reservoir

could mean as little as 10 - 15 strokes or as many as 50 strokes

they do sell brake bleeding kits with clear bleeding hoses , which makes it easier to know when the air is expelled

[rccardude04]

We used the kit that the MC came with that had the clear hoses in it, and it didn't seem to push fluid out any faster than it pulled it in through the hoses. We pumped it a BUNCH. I didn't count, but we did it a bunch. There was one air bubble in one hose (I don't remember which one) that would not go away. It was in the hose permanently. It wouldn't go back down into the master cylinder, but it wouldn't leave the hose out the top either. We're going to try the vacuum pump tomorrow and see how that goes. I'll keep you guys posted.
-Eric

[mechanicaldj]

master cylinders can go bad sitting on the shelf in part houses


and have you checked the combination valve after the master cylinder?

[rccardude04]

Combination valve? the little box thing on the firewall? We haven't checked it but it should create enough vacuum to allow the MC to replenish its brake fluid supply shouldn't it?
-Eric

[rccardude04]

We've almost beat this bad boy!!!!!
Came down to ANOTHER bad master cylinder I guess. We got another one, and the piston was a lot harder to push after a few pumps of bench bleeding. It still didn't work a couple of times after it was on the car, but I finally just got angry at it and we fired it up and I just pumped the pedal pushing about as hard as i could about 50 times and sure enough it started building pressure.
We did discover, however, that the rear brakes are TOAST. You can hold the pedal down firm and actually rotate the rear tires by hand. Parking brake has about the same effect. It seems to hold a little better but not very much.
Anyway, we're about 3 hours and 30 bucks away I think.
I'll post again after we fix it
Thanks for all your help.
-Eric