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74 chev 4X4 bleed prop valve???!


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mbavers
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Jun 17, 2012, 1:35 PM

Post #1 of 20 (1094 views)
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  post locked   74 chev 4X4 bleed prop valve???!  

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?


Tom Greenleaf
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Jun 17, 2012, 2:25 PM

Post #2 of 20 (1064 views)
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  post locked   Re: 74 chev 4X4 bleed prop valve???! [In reply to]  

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
_________________________________________
Long retired now


Hammer Time
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Jun 17, 2012, 2:52 PM

Post #3 of 20 (1050 views)
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  post locked   Re: 74 chev 4X4 bleed prop valve???! [In reply to]  

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.



mbavers
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Jun 17, 2012, 2:56 PM

Post #4 of 20 (1042 views)
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  post locked   Re: 74 chev 4X4 bleed prop valve???! [In reply to]  

I think all parts are good. C clamp I tried was on piston end of proportioning valve. Everything is assembled correctly.


mbavers
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Jun 17, 2012, 3:01 PM

Post #5 of 20 (1037 views)
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  post locked   Re: 74 chev 4X4 bleed prop valve???! [In reply to]  

Bleeder is just slightly above where flex line attaches to caliper.


Hammer Time
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Jun 17, 2012, 3:04 PM

Post #6 of 20 (1031 views)
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  post locked   Re: 74 chev 4X4 bleed prop valve???! [In reply to]  

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.




~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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.



mbavers
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Jun 17, 2012, 3:06 PM

Post #7 of 20 (1025 views)
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  post locked   Re: 74 chev 4X4 bleed prop valve???! [In reply to]  


In Reply To
Go look at your calipers and tell me if the bleeder is above or below the inlet line.

Bleeder is slightly higher than where flex line attaches to caliper.


mbavers
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Jun 17, 2012, 3:08 PM

Post #8 of 20 (1024 views)
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  post locked   Re: 74 chev 4X4 bleed prop valve???! [In reply to]  


In Reply To
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.

Brand new master; bench bled thoroughly.


Hammer Time
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Jun 17, 2012, 3:13 PM

Post #9 of 20 (1019 views)
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  post locked   Re: 74 chev 4X4 bleed prop valve???! [In reply to]  

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,




~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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, 3:14 PM)


Tom Greenleaf
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Jun 17, 2012, 4:27 PM

Post #10 of 20 (999 views)
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  post locked   Re: 74 chev 4X4 bleed prop valve???! [In reply to]  

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
_________________________________________
Long retired now


mbavers
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Jun 17, 2012, 4:28 PM

Post #11 of 20 (993 views)
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  post locked   Re: 74 chev 4X4 bleed prop valve???! [In reply to]  


In Reply To
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,

That's what I thought, but I have read in a few different places that if the positioning valve isn't centered correctly you cannot bleed the system completely. Anyway, I have no pressure bleeding equipment and can't drive to where they do. Maybe I'll be able to borrow or rent one.


Tom Greenleaf
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Jun 17, 2012, 4:34 PM

Post #12 of 20 (988 views)
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  post locked   Re: 74 Chev 4X4 bleed prop valve???! [In reply to]  

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
_________________________________________
Long retired now


mbavers
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Jun 17, 2012, 4:34 PM

Post #13 of 20 (986 views)
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  post locked   Re: 74 chev 4X4 bleed prop valve???! [In reply to]  


In Reply To
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

Bench bleed was done on bench. MC sits level on vehicle. When pedal is depress and I hold finger on rubber boot covering end of piston on positioning valve I can feel end of piston as it slides to the left. I read somewhere to clamp it to prevent movement. Anyway, that didn't help. All bleeding was done by the book.


Tom Greenleaf
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Jun 17, 2012, 4:49 PM

Post #14 of 20 (981 views)
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  post locked   Re: 74 chev 4X4 bleed prop valve???! [In reply to]  

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
_________________________________________
Long retired now


mbavers
User

Jun 18, 2012, 1:52 AM

Post #15 of 20 (956 views)
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  post locked   Re: 74 chev 4X4 bleed prop valve???! [In reply to]  


In Reply To
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,

Hammer Time
You got it! I had the calipers on the wrong sides. Now that I look at it I can't believe I made such a dumb mistake. I just switched sides and did a quick gravity bleed and I've got enough pedal to know it's gonna be OK when I do a complete bleed. THANKS!


Tom Greenleaf
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Jun 18, 2012, 6:09 AM

Post #16 of 20 (949 views)
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  post locked   Re: 74 chev 4X4 bleed prop valve???! [In reply to]  

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
_________________________________________
Long retired now


Hammer Time
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Jun 18, 2012, 6:11 AM

Post #17 of 20 (945 views)
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  post locked   Re: 74 chev 4X4 bleed prop valve???! [In reply to]  


Quote
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.




~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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 18, 2012, 6:13 AM)


mbavers
User

Jun 18, 2012, 12:15 PM

Post #18 of 20 (930 views)
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  post locked   Re: 74 chev 4X4 bleed prop valve???! [In reply to]  


In Reply To

Quote
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.

You asked if the bleeder was above or under the inlet line and it was slightly above it, as I responded to you. Now it is directly at the top.


Hammer Time
Ultimate Carjunky / Moderator
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Jun 18, 2012, 12:20 PM

Post #19 of 20 (923 views)
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  post locked   Re: 74 chev 4X4 bleed prop valve???! [In reply to]  

No, not true. When you flip it over it will be below the inlet. It can't be both.




~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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.



mbavers
User

Jun 18, 2012, 12:36 PM

Post #20 of 20 (918 views)
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  post locked   Re: 74 chev 4X4 bleed prop valve???! [In reply to]  


In Reply To
No, not true. When you flip it over it will be below the inlet. It can't be both.

Due to the angle it sits on it appeared to be slightly above. I did go out and check when you asked this question. Anyway, it is directly at the top now and I should have cought this on my own. Thanks again.




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