Problems replacing my master brake cylinder

[grabowski]

Hey guys,

This is my first post and I'm super thankful that this community exists!

I just bought a 1985 K20 Scottsdale in pretty good condition considering it's 30 years old. My first bit of repair work on it was to replace the old leaky brake master cylinder and I decided to throw in a new power booster as long as I was at it. After bench bleeding the new cylinder, I installed both components into the truck which seemed to go well but I'm now facing two issues:

• I can only push the brake pedal half way to the floor before something stops it from moving
• Using a mightyvac handpump, I am not getting any fluid out of the rear passenger wheel cylinder bleeder

I'm pretty sure that I did not crimp or bend the brake lines during installation. Could this be an obstruction in one of the lines or perhaps a problem with the combination valve?

Any advice here is most appreciated!

[bake74]

     Welcome to the site, you are on the right track.  Retrace from master cylinder, through combination valve all the way back to rear and find out where you no longer get fluid.
     It sounds like you got it handled, maybe just a little stuck with the problems.

[Elpresidente]

What bake 74 said; check for pressure at the cylinder, if none move back to the valve, if none move back to the master cylinder, or any other connection points on the way. As for the pedal, you mean it feels spongy and has no resistance at all until half way to the floor? Is that with the truck running and vacuum going to the booster? Sounds a lot like air in the system to me and likely connected to your problem with the rear passenger cylinder not bleeding because it could be trapping air inside somewhere.

[VileZambonie]

I can only push the brake pedal half way to the floor before something stops it from moving

That's a good thing unless you are saying with a bleeder open or removed.

[grabowski]

Thanks for the replies!

I believe Elpresidente was right and the lines were just clogged with air. So far all of my repair has been with the truck off.

I used the old blow torch trick to release the seized front driver bleeder valve and was amazed by how much air was trapped in the line. Once that line was bled, I was successfully able to bleed the rear passenger cylinder but nothing is coming out of the driver's rear cylinder.

Is it normal for the master brake cylinder to shoot a bit of brake fluid up out of the reservoir a few inches when you hit the brake pedal? I've confirmed that air bubbles are not coming out when I pump the brakes but wasn't sure about the geyser situation.

[bake74]

Is it normal for the master brake cylinder to shoot a bit of brake fluid up out of the reservoir a few inches when you hit the brake pedal? I've confirmed that air bubbles are not coming out when I pump the brakes but wasn't sure about the geyser situation.

     Yes, if the top is off.

[grabowski]

     Yes, if the top is off.

Phew. Thanks!

[78BIG-TEN]

You might take the bleeder out and check for blockage.I see them plugged up all the time

[grabowski]

Alright. I have fluid successfully bleeding out of 3 wheels but the driver side rear is still being stubborn. Even with the bleeder valve fully removed from the cylinder, nothing is coming out.

Must still be some air trapped in the lines somewhere?

UPDATE: That last wheel started to bleed after some vigorous pumping from the pedal. I should be in business now. Thanks again for the advice, guys!