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Discussion Starter · #1 · (Edited)
I've re-assembled my brakes (disc/drum) on my 70 Chevelle.

The problem I'm having is i can't get any fluid at the rear brakes.
I have bled 8-10 times at the fitting before the rear hold off valve and get a good stream of fluid.
After the hold off valve i get nothing. This is a new valve, I had to replace the rear hold off valve and purchased one from Right Stuff. Has anyone had trouble with these new valves?

I basically rebuilt the whole system and had everything off the car except the front distribution block and line running to the rear of the car.

I get a good shot off fluid at the MC bleeder for the rear line when bleeding.
I've gotten a good bleed and pressure on the front.
I've tried bleeding with the car running as well, no luck.

Re-sleeved MC
Rebuilt calipers and wheel cylinders
New rubber lines
New rear hold off

Thanks in advance
Dave
 

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Did you try gravity bleeding? The valve may be holding off the pressure and not letting it pass. But with gravity bleeding there is no pressure. Just something to try.
 

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Out of curiosity did you bleed rear right 1st and than left etc?
I did and got frustrated and started on the front and blew the proportion valve where it moved the valve due to pressure differential and it blocked the rear from getting brake fluid. I had a ccp non adjustable valve. I unscrewed the top where the low pressure brake light connects and used a dental tool and was able to move the valve back to center. The original gm pv have a button you press for these kind of situation,much better design.
Fritz
 

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1. There is no hold-off valve for the rear brakes. The hold-off (also called a "metering") valve is for the front disc brakes when the rears are drums. And the button on the GM combination valve pushes the hold-off valve into a position that allows fluid flow to the FRONT brakes.

2. The valve for the rear brakes is the proportioning valve. IF you have fluid at the inlet to that valve; but no fluid at the outlet--it's defective. Send it back. That valve should do NOTHING until the brake pressure increases to some set point; at which time it reduces the pressure rise compared to the front brakes. At no time should it BLOCK flow. Now, if you really do have a hold-off valve installed there, it'll block fluid flow from about 5 psi until you have ~100 psi in the system--then it should unseat and allow flow. With zero or very very little pressure--it's also open to flow. So it should gravity bleed just fine.

I think you've got a defective proportioning valve--or it's installed backwards, or there's a chunk of rust/crud blocking the port.
 

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Discussion Starter · #5 ·
It seems strange that both Ground Up and Right Stuff call this block mounted on the rear cross over a "Hold Off Valve". I agree that it is performing a proportioning function to the rear brakes.
The fact that i get fluid pressure before it but not after it seems to indicate it may be defective. I'm have to pull it out and check it over.
Thanks
Dave
 

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This is from inline tube's site

This item is an exact reproduction disc brake correction valve. This valve was used to hold off pressure to the rear brakes so the front brakes would go on a split second before the rears. This was also considered a correction valve for several model years. During extreme braking conditions, this valve prevented the rear of the car from washing out sideways and evened out braking loads. Inline Tube has reproduced this valve for every application. This item is an exact reproduction featuring a brass body, the correct bracket, phosphate plating and functioning internals. The reproduction has no tool stamping marks and the edges of the part are cleaner than the original. When you expect the best, Inline Tube is your first choice.



1970 GM F-Body Camaro / Firebird / Nova
1970 GM Chevelle / El Camino / Monte Carlo
1967-69 GM F-Body Camaro / Firebird / Nova
1970 GM A-Body Pontiac GTO / Grand Prix Type of Brakes







Are we talking about the same thing?
 

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Discussion Starter · #7 ·
Yes that is the part. I did buy mine from Right Stuff.
Any ideas why i can't get fluid past it?
The way it mounts and the offset to the inlet and outlet won't allow you to put it in reversed.
Thanks
Dave
 

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This is from inline tube's site

This item is an exact reproduction disc brake correction valve. This valve was used to hold off pressure to the rear brakes so the front brakes would go on a split second before the rears.
That's funny.

The whole point of putting a metering valve into the combination valve body is to PREVENT the front brakes from applying before the rear brakes had enough hydraulic pressure to overcome the brake shoe spring tension.

They may be selling the part; but it seems they have very little idea of what it does.
 

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Discussion Starter · #10 ·
I talked to Right Stuff this afternoon and they are willing to do an exchange. They said they haven't had any trouble with them. If theres a first time it'll be me. Thats usually how it goes.
I'll be pulling the valve out tonight and checking it over before i send it back.
 

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That's funny.

The whole point of putting a metering valve into the combination valve body is to PREVENT the front brakes from applying before the rear brakes had enough hydraulic pressure to overcome the brake shoe spring tension.

They may be selling the part; but it seems they have very little idea of what it does.
The thing that's funny is everyone is missing the key issue!

This is a 1970, it doesn't have a COMBINATION valve. Schurkey, you are correct BUT, for the 70 model, a proportiong valve AND a hold off/correction valve was used in conjunction.

Danhalt, if your proportioning valve looks like this:


Then you have the correct stock set-up. You may have to start removing lines and find where the flow is stopped.
 

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Discussion Starter · #12 ·
I can get fluid to bleed at the rear MC, at theline coming out of the distribution block below the MC and at the inlet fitting of the rear hold down valve. It would appear that the blockage is at the rear hold down valve.
The proportion valve you have pictured is in the front brake circuit and I don't believe it should affect the rear circuit. Correct me if i'm wrong.
 

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I can get fluid to bleed at the rear MC, at theline coming out of the distribution block below the MC and at the inlet fitting of the rear hold down valve. It would appear that the blockage is at the rear hold down valve.
The proportion valve you have pictured is in the front brake circuit and I don't believe it should affect the rear circuit. Correct me if i'm wrong.
You would be correct.

Did you try gravity bleeding??

If so, you probably have crap in the rear hold off/ correction valve. Whatever the real name is.
 

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This info also taken from inline tube's website


In 1969-70 a third valve was added to correct problems from the previous years. This valve now went in the rear line to restrict pressure to the rear because rear drums were now locking up before the front brakes were even activated. By 1971 GM had all the problems worked out and combined all these valves into one valve that is now called a proportioning valve.
 

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Discussion Starter · #15 ·
Tried the gravity bleed thing earlier. No luck.
I was wondering if you would be able to get any fluid past this valve with just gravity?
 

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danhalt, Do you know if your rebuilt master has a residual valve installed behind the rear seat of the MC for the drums ? That might be a problem (not sure) if used with the 70 style rear hold off valve.

I've read info thru the years GM installed residual valve's behind the rear seat on 67 thru 70 disc/drum MC but i have yet to find one on the half dozen or so i've taken apart.
 

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Discussion Starter · #17 ·
danhalt, Do you know if your rebuilt master has a residual valve installed behind the rear seat of the MC for the drums ? That might be a problem (not sure) if used with the 70 style rear hold off valve.

I've read info thru the years GM installed residual valve's behind the rear seat on 67 thru 70 disc/drum MC but i have yet to find one on the half dozen or so i've taken apart.
Well i don't know if i could identify one if i saw one.

I did take the valve out tonight and compared it to my old one. the old one was still working, just a problem with stripped threads.
The old one would allow low pressure air through it in both directions. The new one would not.

Hopefully the new one works better.
 

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This is from inline tube's site

This item is an exact reproduction disc brake correction valve. This valve was used to hold off pressure to the rear brakes so the front brakes would go on a split second before the rears. This was also considered a correction valve for several model years. During extreme braking conditions, this valve prevented the rear of the car from washing out sideways and evened out braking loads. Inline Tube has reproduced this valve for every application. This item is an exact reproduction featuring a brass body, the correct bracket, phosphate plating and functioning internals. The reproduction has no tool stamping marks and the edges of the part are cleaner than the original. When you expect the best, Inline Tube is your first choice.



1970 GM F-Body Camaro / Firebird / Nova
1970 GM Chevelle / El Camino / Monte Carlo
1967-69 GM F-Body Camaro / Firebird / Nova
1970 GM A-Body Pontiac GTO / Grand Prix Type of Brakes


Are we talking about the same thing?

I purchased this valve from inline tube. Installed it (just dressing up the underside) and it would not bleed. I put the old one back in and it worked fine. Inline tube gave me a hard time about returning it for a new one. I will not deal with Inline Tube any more. (this is not the first time I have had problems with their return policy on defective parts)
 

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I can get fluid to bleed at the rear MC, at theline coming out of the distribution block below the MC and at the inlet fitting of the rear hold down valve. It would appear that the blockage is at the rear hold down valve.
The proportion valve you have pictured is in the front brake circuit and I don't believe it should affect the rear circuit. Correct me if i'm wrong.
correct!
 

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Discussion Starter · #20 ·
Right Stuff came through and replaced the defective hold off valve and the new one works as it should.
Thanks
 
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