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Old 09-23-2009, 07:30 PM
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Manuel power brake proportioning valve

Hello guy's I have 77 firebird with t-56 and 350 sbc. Actually , I m removing my power brake master cylinder for a manuel one.
When everything was done and the time of bleeding come , it was impossible to bleed the rear calipers (4 wheels disc brake). When I was doing the conversion , I reinstalled the proportioning valve on the car but now I think it may be my trouble. Do you know if I have to use a proportioning valve with a manuel brake master cylinder
Thanks alot for your help

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Old 09-24-2009, 07:48 AM
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Quote:
Originally Posted by Big_AL
Hello guy's I have 77 firebird with t-56 and 350 sbc. Actually , I m removing my power brake master cylinder for a manuel one.
When everything was done and the time of bleeding come , it was impossible to bleed the rear calipers (4 wheels disc brake). When I was doing the conversion , I reinstalled the proportioning valve on the car but now I think it may be my trouble. Do you know if I have to use a proportioning valve with a manuel brake master cylinder
Thanks alot for your help
Yes, you still will need a proportioning valve. That valve is used to "balance" the brake bias between the front and rear brakes. If it is the "stock" style, check that the piston is still centered. If it is an aftermarket adjustable style and only in the rear lines, close the valve all the way (this will yield 100% flow thru the valve) during the bleeding process. Then re-adjust and test the balance between the front and rear brakes after you have bled the system. The front brakes should lock up just before the rear. This is to prevent "swapping ends" when the brakes are locked up.

Check your pedal ratio. Power brakes usually have around a 4:1 ratio. Non-power (manual) brakes will need a pedal ratio of 6:1 or even 7:1. This will enable you to have the ability to apply enough pressure for the brakes to work well. The manual master cylinder bore should also be slightly smaller than the power brake master cylinder. This will enable more line pressure needed for disc brakes.
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Old 09-24-2009, 02:53 PM
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All right , I m ,gonne try that
Thanks
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Old 09-25-2009, 01:14 PM
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the proportioning valve is a stock one and the piston is in center. I was trying to bleed by gravity but it dosent work Do yout think thats because I m using mastercylinder for rear drum and front disc application.
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Old 09-26-2009, 08:15 AM
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Quote:
Originally Posted by Big_AL
the proportioning valve is a stock one and the piston is in center. I was trying to bleed by gravity but it dosent work Do yout think thats because I m using mastercylinder for rear drum and front disc application.
My question to you. Why are you using a master cylinder that is for front disc and rear drum brakes? You posted that you had 4 wheel disc brakes. That master cylinder may not have enough capacity in the reservoir for the rear disc calipers to fully expand. It also may have a built in residual valve that (in your case) can be removed. The correct master cylinder for 4 wheel disc brakes will have both reservoirs the same capacity and no built in residual valve. Since you are swapping over to manual system (no power) the pushrod hole in the piston of the master cylinder should be much deeper than the original power brake master. This will require a longer pushrod from the pedal to the master cylinder.

I have only bled brake systems using the 'pump the pedal and hold while someone else opens and then closes the bleeder valve, then release the pedal. Repeat until no more air comes out. Go to next wheel.' method so I'll leave comments concerning gravity bleeding to others.
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Old 09-26-2009, 03:37 PM
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I used this master cylinder because I was thinking it can work good , but I m gonne chage it for 4 wheels disc master. I think 72 corvette will work good on it.
Thanks again
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Old 09-27-2009, 05:37 AM
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Order one for a 68 vette manual brake 24.99 at the zone.Works well.
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Old 09-27-2009, 06:50 PM
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all right , I m gonne try that tomorrow
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Old 09-30-2009, 07:14 PM
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I putted a 68 corvette master on it but it dosent work I have some good brakes in front but nothing in the rear wheels. do you have an idea about it?
Thanks again
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Old 09-30-2009, 07:26 PM
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Your going to have to get the fluid to the back first, I had the same problem with my corvette. Take the brake line off at the master cylinder to the front brakes and plug it off for now, And now open the bleeder at the right rear wheel get fluid there and then move to the left rear get the fluid there. once you have fluid at the rear wheels be sure to keep the M/C full at all times Now you can hook the line back at the M/C. And start bleeding the front right then left get the fluid there and you should have it from there. Once you have a good flow at the rear then you can do the front. If none of this works then you may need to start at the distribution block . And i did mine by gravity feed. JMO. Cole

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Old 10-01-2009, 05:32 AM
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All right , thanks for your reply , I gone try that I hope it will wirk.
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Old 10-01-2009, 06:53 AM
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it dosent work again I have some fluid in the back without any air buble but I can turn the wheels with my hand. The front brakes work greatly.
I dont know wath I can do maybe put an air brake systeme
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Old 10-01-2009, 08:46 AM
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You posted that you had 4 wheel disc brakes.

What rear calipers are you using?

If they are the GM calipers with the built in emergency brake, they must be adjusted properly to get them to work. I have attached the instructions below for that. They include a photo of the calipers for you to compare with what you have.

I have also attached info pertaining to residual valves when running the GM caliper in the rear. You may or may not need to add a separate residual valve in the rear line. Adjust the calipers first. Re-bleed the system using the "pump the pedal & hold" method. Then check the brakes for function. If you find that the pads in the rear calipers are retracting more than .015-.020 when the pedal is released, then you should consider adding the aftermarket residual valve in the rear line.
Attached Files
File Type: pdf partsTechBrakeT1008.pdf (215.4 KB, 54 views)
File Type: doc residual pressure valves.doc (25.5 KB, 48 views)
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Old 10-01-2009, 09:05 AM
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I m using 98 mustang rear caliper (because I have an 8.8 rearend) and I m going right now ajusting my emergency brake
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Old 10-01-2009, 12:07 PM
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Quote:
Originally Posted by Big_AL
I m using 98 mustang rear caliper (because I have an 8.8 rearend) and I m going right now ajusting my emergency brake
Calipers installed on the wrong side? The bleeder screw should be the high point (above the fluid inlet).

Russ
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