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I have a 69 Camaro that was 4 wheel drums that I recently converted the fronts to discs using the 13" big brake kit from performance online. I retained the rear drums (for now). I purchased a master cylinder (1" bore) and proportioning valve from Right Stuff at a swap meet. I told the salesman that I was going to run manual brakes and have disc/drum setup. He told me the MC and prop valve is what I needed. I installed the brakes, new stainless lines, bench bled the MC and bled all four corners until I got a good solid stream of fluid. The problem is the pedal is extremely hard...harder than the all four drums were previously. Braking performance is very poor, worse than the all drum setup. I can't get the fronts to lock up, but I can get the rears to lock up rather easily.

I initially thought that maybe I had too large of a MC, but I called POL and they said that they recommend a 1" MC. Could it be my prop valve? Or will I just need to install a booster? Any other ideas? Thanks!
 

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The rear drums take very little pressure to work. You need a prop valve in the rear line to hold off the rear brakes so the fronts can work. Get a knob style prop valve, install it in the rear brake, problem solved.
 

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Use the factory style prop valve that mounts under the MC. Make sure it is the right part number, they look the same. Separate front lines, one rear line - calipers should never lock up under load.
 

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Discussion Starter #4
Thanks for the reply.. Well I thought about the adjustable prop valve, but I called both Right Stuff and POL and they both said that the prop valve I bought was a "fixed" style and I did not need to run an adjustable prop valve. Are you suggesting that I go with an original metering block and use the adjustable prop valve? If so, do you know where I could purchase a metering valve?
 

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Sorry RTL didn't see your post until after I replied. Do you know where I could find a stock style prop valve/metering block?
 

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Metering/hold off valve part number 9223N . It serves as a distribution block and proportioning valve. Year One ?
 

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Did you buy the pol 2" drop with 13" rotors?

As far as your hard pedal, are you certain you have a 1" bore and not a 1 1/8" bore, the corvette masters with 1 1/8" bore come in both shallow and deep hole configurations.
 

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If your 13" front brake kit uses a smaller piston area than stock factory discs, then the prop valve you bought isn't going to work. The kits with late model Corvette or Camaro aluminum calipers all require a much smaller master cylinder.

I tried manual brakes on our 2nd gen Camaro with Baer 13" rotors, the kit came with a 15/16" bore MC, it didn't work, I went down to a 13/16" bore and it would stop if I stood on the pedal, but it wasn't easy enough to drive hard on a race track or autox for repeated laps. I think a 3/4" bore might have worked but I couldn't find one.

I put on the 15/16" bore MC and installed a stock sized power booster with a knob adjust proportioning valve in the rear line, it works perfect. A 1" bore will probably work on a booster system too. I have that on our 68 Camaro with Baer brakes.

David
 

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X3 on the adjustable proportioning valve. You can fine tune it to your cars weight bias and it will still work if you ever go to a 4 wheel disc setup. Factory Proportioning valves are only designed for the stock brake, wheel and suspension set up. They might work with changes to the system but you will be leaving some braking performance 'on the table' without the fine tuning you get with an adjustable unit.
-Matt
 

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If your 13" front brake kit uses a smaller piston area than stock factory discs, then the prop valve you bought isn't going to work. The kits with late model Corvette or Camaro aluminum calipers all require a much smaller master cylinder.

I tried manual brakes on our 2nd gen Camaro with Baer 13" rotors, the kit came with a 15/16" bore MC, it didn't work, I went down to a 13/16" bore and it would stop if I stood on the pedal, but it wasn't easy enough to drive hard on a race track or autox for repeated laps. I think a 3/4" bore might have worked but I couldn't find one.

I put on the 15/16" bore MC and installed a stock sized power booster with a knob adjust proportioning valve in the rear line, it works perfect. A 1" bore will probably work on a booster system too. I have that on our 68 Camaro with Baer brakes.

David
I have 13" Corvette C5 on a 1955 Chevy with LT1 Camaro rear discs. It has a 1 1/8" bore master with 8" booster and non adjustible GM prop valve, brakes workbetter than great.
 

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On my last order from RightStuff, the 4 port master cly was sent to me (ended up leaking) and they sent me a two port and I kept the 4 port. In the box was a bullet looking cone spacer? Fits on the master cly plunger rod? I just wonder it this spacer is in the m/c plunger and you did not notice it and its causing a problem?

I have factory front disc and went to rear disc conversion also. I used the distributon block they sent me , removed my orfice and sold it along with the factory drum brakes.
 
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