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74 chev 4X4 bleed prop valve???!
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mbavers
User
Jun 17, 2012, 10:35 AM
Post #1 of 20
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74 chev 4X4 bleed prop valve???!
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1974 CHEVY 1/2 ton pick-up, full time 4WD, auto trans, front disc brakes, rear drums, 350 engine. Drove after winter lay up and had good brakes, but front pistons seized, so replaced front calipers and let fluid drain out while calipers were off (2 days). Bled, but pedal still went all the way to the floor. Replaced master cylinder (new) after thoroughly bench bleeding. Still no pedal. Tried reverse bleeding front lines by disconnecting front line from master cylinder and pumping fluid in from bleeder and capturing excess at disconnected end of line (at least 1/2 cup from each side). Still no pedal. Parking brake holds. There are no leaks. I disconnected front line again from master cylinder and plugged master cylinder with plastic plug and got some pedal, so it seems the problem is surely in the front. I do not know if the proportioning valve is the culprit-it's the only thing I can think of. Read somewhere to use C clamp on piston end to keep it from extending. Tried this, but same results. The proportioning valve is mounted on the front cross member under the radiator. It also contains the brake warning light switch. Anyone know for sure how this valve is supposed to be clamped or held while bleeding brakes? Could the problem be anything else?
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jun 17, 2012, 11:25 AM
Post #2 of 20
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Re: 74 chev 4X4 bleed prop valve???!
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Long time ago so digging at memory only. It's a combination valve. Some (perhaps only Fords) had a button to push on the valve. Other trick was to pump, hold and release pressure to rear brakes to center the thing but don't allow air in.
Do rear brakes bleed out at all? What is the rust situation with the parts - lines everywhere, bleeder to wheel cylinders or any other observations that might help figure it out? It's old enough for several possibilities.
Instead of using a "C" clamp for bleeding on the piston why not just put them back on? Can't say if that is flexing too much or what.......
T
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Hammer Time
Ultimate Carjunky
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Jun 17, 2012, 11:52 AM
Post #3 of 20
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Re: 74 chev 4X4 bleed prop valve???!
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Go look at your calipers and tell me if the bleeder is above or below the inlet line.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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mbavers
User
Jun 17, 2012, 11:56 AM
Post #4 of 20
(2898 views)
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Re: 74 chev 4X4 bleed prop valve???!
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I think all parts are good. C clamp I tried was on piston end of proportioning valve. Everything is assembled correctly.
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mbavers
User
Jun 17, 2012, 12:01 PM
Post #5 of 20
(2893 views)
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Re: 74 chev 4X4 bleed prop valve???!
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Bleeder is just slightly above where flex line attaches to caliper.
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Hammer Time
Ultimate Carjunky
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Jun 17, 2012, 12:04 PM
Post #6 of 20
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Re: 74 chev 4X4 bleed prop valve???!
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OK, just making sure the left and right weren't switched.
Try pinching off the flex hoses to all 4 wheels and bleed the master. If you can't get a pedal that way, then i would suspect a bad master.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Hammer Time
Ultimate Carjunky
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Jun 17, 2012, 12:13 PM
Post #9 of 20
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Re: 74 chev 4X4 bleed prop valve???!
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This isn't rocket science. you have a dinosaur with no ABS or anything else fancy. If all the wheels are dead headed and it has no leaks, the master and bleeding it are the only thing left in the system. Use a pressure bleeder if you have to,
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
(This post was edited by Hammer Time on Jun 17, 2012, 12:14 PM)
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Tom Greenleaf
Ultimate Carjunky
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Jun 17, 2012, 1:27 PM
Post #10 of 20
(2855 views)
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Re: 74 chev 4X4 bleed prop valve???!
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This is messing me up. What's with a "C" clamp on a proportioning valve? A good one should reset to center by itself. Yes, some even then would throw fits to bleed out but finally did for me anyway.
Pressure bleeding as HT said would prove air is out and they force a bit more volume than plain pumping brakes. If no pedal then, then I too blame the new master. Don't think this one sits at a steep angle on booster as at least some GM cars did but if not level it won't do a bench type bleed while installed.
One more - are you using a helper pumping brake, holding while bleeder is open and not releasing the brake pedal till bleeder is closed again? If not - it's just sucking air back in,
T
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Tom Greenleaf
Ultimate Carjunky
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Jun 17, 2012, 1:34 PM
Post #12 of 20
(2844 views)
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Re: 74 Chev 4X4 bleed prop valve???!
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Look back as we both posted at about the same time. If (never happened in the decades of working on these) a proportioning valve was firmly stuck it may have to go but make sure if so it's exactly = to the OE one,
T
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Tom Greenleaf
Ultimate Carjunky
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Jun 17, 2012, 1:49 PM
Post #14 of 20
(2837 views)
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Re: 74 chev 4X4 bleed prop valve???!
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The only thing from my work on those when not so old is that they were all 2WD and there might be some difference. Almost all would just plain "gravity" bleed out when all was well.
I'm in and was then in rusty New England. Two family owned and all others I knew of rusted so fast it was like they were designed to on purpose rendering them near useless in short order or too expensive to fix body rust. They ran great otherwise and pretty basic to work on,
T
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Tom Greenleaf
Ultimate Carjunky
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Jun 18, 2012, 3:09 AM
Post #16 of 20
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Re: 74 chev 4X4 bleed prop valve???!
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Jeez - Hammer hit that one early!
Thread locked to save you from spammers as I think you are all set. Any moderator can unlock it or just start a new thread if need be.
Good luck,
Tom
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mbavers
User
Jun 18, 2012, 9:15 AM
Post #18 of 20
(2786 views)
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Re: 74 chev 4X4 bleed prop valve???!
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Hammer Time
You got it! I had the calipers on the wrong sides. So you're saying that you were also wrong when I asked you to check that?.............. or you didn't even check it? edit, i unlocked it for now. I want to hear the answer to my question.
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Hammer Time
Ultimate Carjunky
/ Moderator
Jun 18, 2012, 9:20 AM
Post #19 of 20
(2779 views)
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Re: 74 chev 4X4 bleed prop valve???!
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No, not true. When you flip it over it will be below the inlet. It can't be both.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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