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Discussion Starter · #1 ·
I just put new '69 front disc brakes on my 68SS. I installed a new manual disc MC from a 69 corvette per the recommendations on this site. I then installed a Speedway motors adjustable proportioning valve in the rear line after the distribution block. I have a gauge on the rear brake side of the valve and cannot get it to read any pressure, no matter what the adjustment. I did bleed the front line and did get some air from the rear.

Would my new MC use a different pushrod then my stock manual drum MC?

I did a bench bleed on the MC before installation. The front calipers seem to be actuating, but the rear drums will not even grab enough to stop the wheel from free spinning. Any help would be greatly appreciated.

I really need to get these brakes fixed so I can drive away from my wedding next week!!

Thanks
 

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I had a similar situation when I upgraded to disc on my son's car. We ended up having to bleed the brakes at the master cylinder even though it was bench bled. Worth a try. Pete
 

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I just rebuilt the brakes on my 69. I had a problem with the factory hold off valve sucking air. I removed it from the system and installed a brass coupler in it's place to bleed the system. After they bled, I drove it and the brakes work perfect. All four grab under a hard stop.

What I am trying to say is if you are having a problem with rear lockup Then add a prop valve, or you may be throwing away money on something you don't need.

Try taking the valve out and see if they bleed/operate OK.
 

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I just put new '69 front disc brakes on my 68SS. I installed a new manual disc MC from a 69 corvette per the recommendations on this site. I then installed a Speedway motors adjustable proportioning valve in the rear line after the distribution block. I have a gauge on the rear brake side of the valve and cannot get it to read any pressure, no matter what the adjustment. I did bleed the front line and did get some air from the rear.

Would my new MC use a different pushrod then my stock manual drum MC?

I did a bench bleed on the MC before installation. The front calipers seem to be actuating, but the rear drums will not even grab enough to stop the wheel from free spinning. Any help would be greatly appreciated.

I really need to get these brakes fixed so I can drive away from my wedding next week!!

Thanks
:confused:did the new MC have a deep or shallow pushrod contact area?
it should match the old one, or a different pushrod is indicated....

if you only got a little air out of the rear bleeders then you may still have air in the lines, also the valve in the distribution block on the frame may be stuck, blocking pressure to the rear brakes. this would mean centering the distro-block valve and retrying to bleed the brakes. hope this helps. you could do a search for a similar problem and see how it was fixed. good luck.:thumbsup:
 

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Discussion Starter · #5 ·
All good suggestions. How do I recenter the dist. block valve? Do I only need the porp.valve on the rear line if I am having problems with the rears locking up?

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To re-center the dist. block you have to take a line off and push it to center with a small screwdriver or pick. I have never had a problem with this, but some have.

First I would remove the adjustable prop valve, you might as well check the dist block while the system is open. Couple the lines together so you can install it later if needed, then gravity bleed the rears. You do this the same way as pumping but without the pumping. Start at the right rear and let the fluid drain put your finger close to the bleeder so that the fluid touches your finger as it's coming out. This way you can see the bubbles easier when they come out. Let it run untill all the bubbles are gone.

After it gravity bleeds check the pedal and see how it feels. I didn't have to pump mine, gravity bleeding did the trick. If it feels good, drive it and see how it stops. If you are confident they will stop you and not do something unpredictable, Get it up to speed and hit em' hard. If the rears are locking up, then install your adjustable prop valve.

You want all the braking power you can get. If the rears are locking up then you are losing braking power. If the are not locking up, but they are grabbing, then they are doing their job. In this case the adj. prop. valve would make your braking power even weaker.
 

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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.
I spend days on this same problem with air hose bleeder and all the vaccum patience was key but everything has to be right. MC has to be bench bleed. MC rod is different when going from manual to power. The difference is quite noticeable. But that is not your issue!
Fritz
 

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1. Most (I hate to say "all") General Motors brake light switches are spring loaded; they'll center themselves AFTER you fix the hydraulic system. Any that aren't (Ford comes to mind) will center by having a helper step on the brake pedal and then just barely bleeding either the front or the rear brakes--whichever hydraulic system DIDN'T have the original problem.

2. The "button" that gets pressed on the GM combination valve is not for the warning light, it's used when bleeding the FRONT (not rear) brakes with a pressure bleeder.

In practice, I've NEVER needed to screw with it. You WON'T need to press the button when bleeding by pressing the brake pedal; and you WON'T need to press the button when gravity bleeding. If there's fluid coming out of the front caliper bleeders, you don't need to dick with the button.



First Guess: You still have air trapped in the master cylinder. Does the master tilt up in front? If the master is tilted, and there's air in it, you'll NEVER get the air out until you unbolt the master from the booster or the firewall, pull it off the studs, level it, and tickle the piston. Then the air will bubble up through the compensating ports into the reservoirs. DON'T unscrew the brake tubes when you do this.
 

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1. Most (I hate to say "all") General Motors brake light switches are spring loaded; they'll center themselves AFTER you fix the hydraulic system. Any that aren't (Ford comes to mind) will center by having a helper step on the brake pedal and then just barely bleeding either the front or the rear brakes--whichever hydraulic system DIDN'T have the original problem.

2. The "button" that gets pressed on the GM combination valve is not for the warning light, it's used when bleeding the FRONT (not rear) brakes with a pressure bleeder.

In practice, I've NEVER needed to screw with it. You WON'T need to press the button when bleeding by pressing the brake pedal; and you WON'T need to press the button when gravity bleeding. If there's fluid coming out of the front caliper bleeders, you don't need to dick with the button.



First Guess: You still have air trapped in the master cylinder. Does the master tilt up in front? If the master is tilted, and there's air in it, you'll NEVER get the air out until you unbolt the master from the booster or the firewall, pull it off the studs, level it, and tickle the piston. Then the air will bubble up through the compensating ports into the reservoirs. DON'T unscrew the brake tubes when you do this.

I was refering to the front button that will center the valve back to center on the PV valve. My CPP pv does not have one and when you dont have one there is a method that you use but on mine the valve was stuck completly.
I spend many hours on that pv. If bought another one I would highly recommend the pv with the bleeder button. The warning light is hooked up to the center on my pv. So when there is a pressure differential the warning light will come on. This will unscrew on my pv and you can center the valve back with a sharp dental tool,just my humble experience. When all fails.
I converted to 4 wheel disc and bench bleed made new lines and it took me forever to get fluid to come ouf the back. This is espcially true when replacing brake lines.
Fritz
Fritz
 
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