Difference in Master Cylinder Bore Sizes

Detroit Iron · Feb 13, 2016

Why are there different bore sizes for disc brake master cylinders? I need to replace mine and don't remember what the reason is for the different sizes. Thanks!!

Mancini lists a 1.125" and a 1.032".

65 3 times · Feb 13, 2016

Power or manual will make a difference . If you have been happy with your brakes match the size you have. Dave

Detroit Iron · Feb 13, 2016

Thanks for the input. I don't know what size I have. Do you know what size is for manual, and what size for power?

65 3 times · Feb 13, 2016

If they are stock parts enter year and model on internet parts site. It will give you a part # and specs. on part. Dave

lewtot184 · Feb 13, 2016

manual is usually 1" and power may be as big as 1 1/8". i use a 15/16" for my disc/drum manual combo; works very good.

Kern Dog · Feb 15, 2016

The larger the bore size, the more effort it takes to press the pedal but the brakes will react with less pedal travel due to the greater volume of fluid in the same amount of travel. You may have to read that 3 times to understand....I certainly did.

Power brake systems can get by with larger bore sizes because the booster reduces pedal effort. Power brake systems also have different pedal ratios as compared to manual brake cars. Pedal ratio relates to the amount of leverage between the brake pedal, through the linkage and on to the master cylinder.

Mopars & Missiles · Feb 15, 2016

I'm going to give it a shot to try to clarify what some have been trying to say in this thread.

Large M/C bore size = more fluid volume flow to wheel cylinders/calipers, BUT also LESS line pressure (PSI) to same.
Small M/C bore size = less fluid volume flow to w/cyl/& calipers, BUT also MORE line pressure (PSI) to same.

Now, the consequences of these differences.

Higher fluid volume = less pedal travel
Lower fluid volume = more pedal travel

Drum brakes generally require about 750-1000 PSI line pressure to work well.
Disc brakes generally require about 1200-1600 PSI line pressure to work well.

Hope this helps!

Difference in Master Cylinder Bore Sizes

Detroit Iron

Well-Known Member

65 3 times

FBBO Gold Member

Detroit Iron

Well-Known Member

65 3 times

FBBO Gold Member

lewtot184

Well-Known Member

Kern Dog

Life is full of turns. Build your car to handle.

Mopars & Missiles

Well-Known Member

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