Master Cylinder Selection

[mcmlxix]

I have a 72 K5 Blazer with upgraded disc brakes.

The rear axle is an AAM 14BFF from a 2005 Sierra 2500 with twin piston calipers and 13 inch rotors with built in E-brake. Rear axle total piston surface area is 12.69232 inches (4 pistons total.)
The front axle is a Dana 60 with custom brakes from a 2009 Dodge 3500 with 14 inch rotors at 1.5 inches thick. The front axle total piston surface area is 18.09556 inches (4 pistons total).

I am running a 2005 GM Hydro-boost. The GM master cylinder bore was 1.3125 inches but the donor for the Dodge front brakes had a master cylinder bore of 1.456 inches.

I was looking at the Baer Brakes Remaster master cylinder but its only offered in 1.125 inch bore. Will this work and what can I expect from the difference in MC bore size?


FRONT BRAKES
2009 Dodge Ram 3500 HD
Master Cylinder bore: 1 5/16 ~ 1.3125 inches
Front caliper piston bore: 2.4 inches (2 per caliper)
Front caliper piston surface area: 4.523893421169302 (2 per caliper)
Front axle total piston surface area: 18.09556
Front Rotor Diameter: 14.173 inches

REAR BRAKES
2005 GMC Sierra 2500
Master Cylinder Bore: 1 7/16 ~ 1.456 inches
Rear caliper piston bore: 2.01 inches (2 per caliper)
Rear caliper piston surface area: 3.17308711994203 (2 per caliper)
Rear axle total piston surface area: 12.69232 inches
Rear Rotor Diameter: 13 inches

[mongocanfly]

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[mcmlxix]

Originally Posted by mcmlxix

I have a 72 K5 Blazer with upgraded disc brakes.

The rear axle is an AAM 14BFF from a 2005 Sierra 2500 with twin piston calipers and 13 inch rotors with built in E-brake. Rear axle total piston surface area is 12.69232 inches (4 pistons total.)
The front axle is a Dana 60 with custom brakes from a 2009 Dodge 3500 with 14 inch rotors at 1.5 inches thick. The front axle total piston surface area is 18.09556 inches (4 pistons total).

I am running a 2005 GM Hydro-boost. The GM master cylinder bore was 1.3125 inches but the donor for the Dodge front brakes had a master cylinder bore of 1.456 inches.

I was looking at the Baer Brakes Remaster master cylinder but its only offered in 1.125 inch bore. Will this work and what can I expect from the difference in MC bore size?


FRONT BRAKES
2009 Dodge Ram 3500 HD
Master Cylinder bore: 1 5/16 ~ 1.3125 inches
Front caliper piston bore: 2.4 inches (2 per caliper)
Front caliper piston surface area: 4.523893421169302 (2 per caliper)
Front axle total piston surface area: 18.09556
Front Rotor Diameter: 14.173 inches

REAR BRAKES
2005 GMC Sierra 2500
Master Cylinder Bore: 1 7/16 ~ 1.456 inches
Rear caliper piston bore: 2.01 inches (2 per caliper)
Rear caliper piston surface area: 3.17308711994203 (2 per caliper)
Rear axle total piston surface area: 12.69232 inches
Rear Rotor Diameter: 13 inches

Here is the response from Baer technical support....

Unfortunately, with this I can say that I would NOT suggest using the 1.125” Remaster. While it would bolt up, it would not provide anywhere near enough volume of fluid causing excessive pedal travel. This along with the additional assist from the hydroboost and higher line pressure of the smaller master would also make for a super sensitive brake once the brakes did start to grab.

As for what size master to run, I would probably stick with the master size from the donor calipers assuming everything else is equal. Pedal ration and booster type.