Brakes - round 3 of a 4 round battle

[don t. - 72gmc]

God, I edited this and its still long. I wanted to remove more but stay informative.

Started 8 weeks ago, a complete brake r&r. Why? Front pass was only thing stopping truck, pedal needed help comming up, seepage in 2 middle sections of the hard lines.
Replaced wh. cyls, 3 flex hoses, hard lines, fr. calipers, mstr cyl., turned rear drums, had to replace fr. rotors (bearings/grease seal just cuz I was there). Used old prop. valve and front T fitting. These I cleaned up/blew comp. air thru. Prior owner had replaced pads, shoes, one section of hard line.
Got it back together Sat. afternoon. Bench blead mstr., installed. Gravity blead(mstr cover off), started w/rears. Worked ok, then flow stopped. Figured since its a dual master, grav blead fronts, no problem. Still no flow from rear. I had 1 leak to rear, 1 to front, both couplings needed tightening. Still no rear flow.
Sunday...neighbor helped w/manual bleed(mstr cover just sitting on mstr). Started w/rears, doing great, both sides(had a leak by rear flex hose, fixed). Did fronts in half the time of rears, no problem, flow great.
Here's where problem starts. Went back to rear dr. side, flow started to decrease. Rear pass side same. Went back to fronts, started good and got worse/same as rears. Took 45 mins to bleed 12 oz. bottle thru system. Called brother who said master cover needed to be sealed/clipped down and start over. Bench blead mstr, no prob. and reinstalled. Blead thru prop valve, no problem. Connected prop valve. Blead almost 1 qt. thru entire system (took almost 2 hrs.), nothing more than drops, no stream unless I let everything sit for 10 minutes or more. Multiple pumps on pedal help only on first bleed at each corner, then decreases even if you increase pedal pumps.
At this point
A - i've never ran into the above. Its all new parts, from NAPA, what the muck!
B - I just don't know. Brother says keep bleeding but 1 qt. over 2 hours and no better. I trust him but?????
C - the wife is ticked that this "thing aint done". Like this helps!!!
Any help is greatly appreciated!
.....don t. .....

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It aint gonna be a trailer queen, its gotta work, just like me.
3/4 ton,350 w/HEI, 79 q-jet, th400, Dana 60.


[This message has been edited by don t. - 72gmc (edited May 20, 2002).]

[This message has been edited by don t. - 72gmc (edited May 20, 2002).]

[bigvinnie]

sounds like something that's common to all 4 corners, like master cylinder or prop valve... I would probably try a second master cylinder as a reality check...

when you bleed each wheel cylinder, does the pedal go to the floor or does it get tight and stop short? if it goes to the floor and you only get drops, fluid is most likely slipping around master cylinder push rod.... if it gets tight and stops short, you 've got some blockage, either in the mc, prop valve, T fittings, or lines... process of elimination. Good Luck.

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'72 short step, 350, 700R4, tilt, ps, pdb, a/c, lowered coils, etc., other work in progress... San Diego, CA
http://www.ixpres.com/vlusardi/chevtrk.htm




[This message has been edited by bigvinnie (edited May 20, 2002).]

[Blue68]

Bled mine the other day. I had similar results in the rear, but it got better. Problem was I flipped the prop valve when I moved it out of the garage without having bled the lines. So the rears weren't getting much of any pressure (like one bubble at a time).

Does your brake light come on when you turn on the key?

Odd thing is, you get it on both ends. I'm assuming the engine isn't running while you do this. If it is, when you open a bleeder and with pressure assist, you will flip the prop valve and it will more or less shut down flow to the front/rear system where you opened it up.

If that's not the case, it's strange. You should be able to go through a can of brake fluid in about 10 minutes of steady work. I just about sucked the rear dry on my truck ONCE it started to flow. Again, got to get the pressure equalized if the prop valve has tripped.

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'68 C-10 LWB, '98 Z-71 350 w/accessories (Serpentine), Edelbrock Performer, Edelbrock 1405 (600cfm) carb, GM HEI, CompCam Extreme 4x4 roller cam, Thorley Headers, Carter Electric Fuel Pump, Vintage Air, 700r4, 3.73, disc brakes and power steering upgrades.


Way too much money and time..But it's a hobby.

[CoryM]

Definatly sounds like you tripped your proportioning valve. it will block off the pressure to the rear wheels if there is a leak. There is a little button you have to push to center it again, then be careful not to pres the pedal too far when bleeding next time. Remember, that little valve doesnt move for 30 years then all the sudden does, gonna be a little sticky. Good Luck, let us know.
CoryM


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1970 heavy duty C-10 fleetside sport truck. Vancouver B.C. Canada
http://www.geocities.com/chevroletc1070


"Take up our quarrel with the foe:
To you from failing hands we throw
The torch; be yours to hold it high."
Lieutenant Colonel John McCrae, Canadian Army

[1-PU70]

Check how deep the bore is on the rear of the master and then mesure how far the rod sticks out of the Booster. The rod should be just a little shorter then the bore.