Another Brake question, tearing my hair out

[centexan]

Evening folks. Having a bit of an issue with my brakes and was hoping I could get some insight from you. '89 v1500 Suburban. I felt it was time for an overhaul of the brake system. Had leaky rear wheel cylinders so replaced those, all soft hoses, new rear shoes, new front calipers and pads, new master cylinder and after trying to chase down the issue, new brake booster today.

Bench bled the new master cylinder, used compressor driven vacuum tool to bleed the air out of the lines, then bled them traditional way (numerous times to make sure we got the air out). When turned off, have firm, high pedal. Turn the truck on, pedal gets spongy and sinks. Replaced the brake booster and it's about the same, except the pedal doesn't rebound as quickly. When I press the pedal from inside the cab, the rear chamber in the master cylinder seems to either gurgle or spout brake fluid up into the cover and the brake booster seems to flex forward. Is that normal. We've spend 4 afternoons this weekend trying to figure it out. Thanks in advance for your help!

[franken]

Brake feel is subjective. Action is different. The front brakes provide ~75% of braking and the rears provide a lot of feel. Drive it.
Start the engine w/ the foot on the brake and the pedal will drop a bit if the booster is good.
I don't think spitting fluis w/ the cover off is abnormal.

[homemade87]

Is the master cylinder one of those alum ones with the large piston on the rear side ( dual bore size ) . If so you may not have it bleed correctly yet . Those things are a pain to bleed . When you think you got the air out bleed , bleed , & bleed some more . Tip it back and forth while bleeding let it set and do it again . Took me about an hour to get mine right . I could not believe how much more air came out of that dual bore master after all I had done to it . There is a proper tool to bleed those but most will not have one . I was fighting a soft pedal as well . Take a look on the net , should find some info on it . You will have to take it back off to do this .

[JMMotor]

My guess you got pockets of air still stuck in system. Does the truck have rear anti-lock? Might have some air stuck in valving. Try driving and locking-up the brakes to get the anti-lock to activate, that'll push the air through to the rear. Another trick for those aluminum master's is to jack the back up as high as you can so the master cylinder is level and then bleed master, front and rear brakes.

[GM-power]

When you're driving, if you pump the brakes do they firm up?

[oldpurple]

I recently dealt with two re-manufactured master cylinders that didn't work straight out of the box. Don't assume it's not the issue because it's a new part.