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 Post Posted: Wed Jun 29, 2016 7:59 pm 
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Location: Malin OR
Installed the front blazer spindles with the 2 piston calipers. Also installed the rear disc of a 97 olds bravado(mad my own caliper brackets). Rear is a 12 bolt Chevelle Have changed the prop valve to a 4WD valve. 7/8 bore g body master cylinder. System doesn't seem to flow enough fluid causing low pedal. Most of the time need to pump the pedal. Any ideas on a master cyl that would work good?

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1987 Monte Carlo aero coupe on Alky
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 Post Posted: Wed Jun 29, 2016 8:35 pm 
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Location: Houston, TX
To help with a low pedal, make sure you have new rubber brake lines front and rear or upgrade to stainless steel flexible lines. Old rubber lines will start to balloon with age when pressure is applied and cause a low pedal

You can upsize the master cylinder to a 24mm master cylinder.

If you bought the kit through manualbrakes.com, I will send out a 24mm master cylinder that will bolt in place at no extra charge.

Let me know if you have additional questions.

Call, text, or email.
832-264-5566
david.schultz@manualbrakes.com

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Last edited by malibudave1978 on Sat Dec 10, 2016 1:11 pm, edited 1 time in total.

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 Post Posted: Thu Jun 30, 2016 9:43 am 
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Thanks for the input. Thought about putting ck valves in. Had some in a friends car but with the master in the stock location the brakes dragged enough to make it harder to turn the wheel than I liked when off the ground. took them out. Have braided hoses for the lines. Maybe a larger master will do it but how much more effort will be involved?

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1987 Monte Carlo aero coupe on Alky
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 Post Posted: Thu Jun 30, 2016 8:59 pm 
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Location: Houston, TX
If you plug both ports of the master cylinder, does the brake pedal firm up with almost no movement?

I want to make sure that the master cylinder is functioning correctly before you change out the master cylinder.

If you plug the rear port of the master cylinder that goes to the front brakes, does the pedal firm up?
And after reattached the brake line back to the rear port...
If you plug the front port of the master cylinder that goes to the rear brakes, does the pedal firm up?

I would want to know which end is giving you the issues. Is it the front brake system giving you issues, or is the rear brake system given you issues? Does the pedal effort for each stay the same between the two tests?

Here are the inputs that are that will apply to both sizes of master cylinders.

• 6 to 1 pedal ratio
• 25.5” tall tire
• 100 ft/lb pedal pressure
• Manual Brakes – NO POWER ASSIST
• Pad Coefficient of Friction - .45
• Use of stock type (tandem) master cylinder

24mm Master Cylinder
Twin 46mm diameter Piston Caliper with 24mm bore master cylinder.
• Rotor Diameter – 10.5”
• 24mm Bore Master Cylinder Area - .701 sq-in
• Line Pressure – 856 psi
• Front Caliper Piston Area – 5.152 sq-in
• Front Clamping Pressure – 4410 pounds
• Front Rotor Torque – 868 ft/lb
• Tire Forces – 817 lb

46mm diameter REAR Piston Caliper with 24mm bore master cylinder.
• Rotor Diameter – 11.6”
• 24mm Bore Master Cylinder Area - .701 sq-in
• Line Pressure – 856 psi
• Front Caliper Piston Area – 2.81 sq-in
• Front Clamping Pressure – 2401 pounds
• Front Rotor Torque – 523 ft/lb
• Tire Forces – 492 lb

TOTAL TIRE FORCE W/ 24mm MASTER CYLINDER: 2540 lb
_________________________________________________________
_________________________________________________________

7/8" Bore Master Cylinder
Twin 46mm diameter Piston Caliper with 7/8" bore master cylinder.
• Rotor Diameter – 10.5”
• 7/8" Bore Master Cylinder Area - .601 sq-in
• Line Pressure – 998 psi
• Front Caliper Piston Area – 5.15 sq-in
• Front Clamping Pressure – 5142 pounds
• Front Rotor Torque – 1012 ft/lb
• Tire Forces – 952 lb

Single 46mm diameter REAR Piston Caliper with 7/8" bore master cylinder.
• Rotor Diameter – 11.6”
• 7/8" Bore Master Cylinder Area - .601 sq-in
• Line Pressure – 998 psi
• Rear Caliper Piston Area – 2.81 sq-in
• Rear Clamping Pressure – 2799 pounds
• Rear Rotor Torque – 610 ft/lb
• Tire Forces – 574 lb

TOTAL TIRE FORCE W/ 7/8" MASTER CYLINDER: 3052 lb
_________________________________________________________
_________________________________________________________

From the calculations above you will loose roughly 150 psi of line pressure going to a 24mm bore master cylinder. This translates to lower clamping pressure and rotor torque that you will have to compensate by pushing harder on the brake pedal. You will notice the effort.

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 Post Posted: Fri Jul 01, 2016 10:46 am 
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MalibuRacing Junkie
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Do you have the pushrod in the right hole on the brake pedal?

Tommy

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 Post Posted: Fri Jul 01, 2016 6:56 pm 
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LS6 Tommy wrote:
Do you have the pushrod in the right hole on the brake pedal?

Tommy



guess so. In the one that lines up with the master. Lower hole I believe.

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 Post Posted: Fri Jul 01, 2016 7:47 pm 
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The lower hole is for power brakes; the upper hole is for manual brakes.


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 Post Posted: Fri Jul 01, 2016 9:10 pm 
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t5montecarlo wrote:
The lower hole is for power brakes; the upper hole is for manual brakes.



will have to look. Brakes seem ok once I get a pedal.

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 Post Posted: Sun Jul 10, 2016 8:02 am 
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They will feel even better if you use the upper hole.


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 Post Posted: Sun Jul 10, 2016 10:03 pm 
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Could someone please take a quick pic of the "2 holes" that are in the brake pedal and which one to use with either manual or power brakes? My BBC Malibu has a serious brake deficiency and the p.o. converted it to manual. Seems ok with regards to pedal height and effort (for the most part), but at high speeds, I can stand on the pedal, and it seems like I could open the door, and drag my foot to get the car to stop quicker. Has a Ford 9" rear with a disc conversion, too. Apparently, he has the popular "Corvette" master cylinder that most people do for this type of conversion. Now that I'm sorting the car out, and converting it from an ex drag car to a nice street/strip car, I'd like to tackle the brakes next.

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1979 Malibu Coupe BBC M21 4 speed the "Big Gun"
1979 Malibu Coupe LQ9 TCI 6X
1979 Malibu Wagon 305 TPI 700R4


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 Post Posted: Mon Jul 11, 2016 7:18 am 
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MalibuRacing Junkie
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The upper hole is for manual brakes; the lower hole is for power brakes. Though all pedals have both holes, the pin is only in 1 hole. A manual brake car uses a small brake pedal pad, just like a manual transmission car.

The factory pin for power brakes is a different diameter than for power brakes. I don't recall which is larger or smaller, but figure the difference in diameter prevents the wrong hole from being used in the wrong application.

Here is a picture of a manual brake pedal that I may still have. The pedal came from an automatic car.
Image


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 Post Posted: Tue Jul 12, 2016 9:55 am 
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Thanks T5! I'm going to confirm I have the pin in the correct hole. Step one, lol.

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1978 Malibu Coupe SBC TH350
1979 Malibu Coupe BBC M21 4 speed the "Big Gun"
1979 Malibu Coupe LQ9 TCI 6X
1979 Malibu Wagon 305 TPI 700R4


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