bigger master cylinder bore

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bigger master cylinder bore

Postby chevy art » Fri Feb 18, 2011 2:45 am

i believe that increasing the size of the bore in the master cylinder (say 3/4 to 7/8) lowers the line pressure. does this make the pedal softer or harder to push in ? i would think softer is the answer, but just dont get it. hate to sound dumb, but i dont remember the answer and i know it has been discussed many times. thanks art
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Re: bigger master cylinder bore

Postby 3pedals » Fri Feb 18, 2011 4:33 am

Art:
You're half right. Pedal pressures being the same, a larger bore will create less line pressure.

After adding the larger bore the pedal needs more pressure to create the same amount of braking force.

I'm not sure if that answers your question....
Last edited by 3pedals on Fri Feb 18, 2011 12:46 pm, edited 2 times in total.
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Re: bigger master cylinder bore

Postby Fastmax32168 » Fri Feb 18, 2011 7:03 am

Bigger bore equals harder pedal.
Smaller bore equals softer pedal.
The smaller bore requires you to move the pedal further in order to transfer the same amount of fluid.
Basically the smaller bore is just a bigger lever. As a lever gets longer, it requires less force to move it, but more distance.
A shorter lever requires more force to move, but you dont have to move it as far.
If you were to make the pedal itself a foot longer it would accomplish the same thing as a smaller bore.
You would have to move it further, but it would require less force to do it, and it would require less pressure to stop the car.
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Re: bigger master cylinder bore

Postby chevy art » Fri Feb 18, 2011 8:45 pm

thanks guys you each answered parts of my question. now i know how things will react when i install the monza discs on my 75 vega. hopefully nothing will change, but , like a good boy scout, i will be prepared art
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Re: bigger master cylinder bore

Postby 454spyder » Tue Feb 22, 2011 9:27 pm

If you go 4 wheel discs, install a Corvette C3 master cylinder. It is a bolt-in (at least it was when I installed one on my 77 Monza). Now that I think of it, I got rid of the power booster and the vette's manual 4wheel disc M/C bolted right up to the firewall and used the original rod/cup also I think (its been a while). I believe the the power version worked the same way.

Also if you go 4 wheel discs, you should replace the brake line going to the back - its a larger diameter designed for drum brakes. The discs use smaller lines for more pressure.
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Re: bigger master cylinder bore

Postby chevy art » Tue Feb 22, 2011 10:50 pm

thanks for the reply 454 spider my 75 vega has a ford rear with the large shoes and the 76 monza disc setup in front., so i am giong to try the stock 75 master and distribution valve to start (i believe cj biaji used this very setup with no issues.) if that dont work, then i will step up one n otch to the 76 monza master cylinder and distribution block. this has a 7/8 bore size. the stock 75 vega MC has a 3/4 inch bore size. art
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Re: bigger master cylinder bore

Postby burnouts&rotorblades » Sat Mar 07, 2020 1:36 am

I know this is an old thread, but I wanted to add some information. It was a good discussion but was kind of incomplete.

The bore size of a stock 1972 Vega brake master cylinder is .75" power or manual brakes makes no difference.

A C3 Corvette master cylinder (I used a power 1972 corvette M/C) has a bore of 1.00" for manual and 1.12" for power brakes.

With a 1972 Chevrolet Corvette power brake Master cylinder:
The brake pedal feel is rock solid. The petal moves about 1" with a significant amount of leg effort before locking up all 4 wheels. This makes heel-and-toe downshifting impossible. I
It did not come equipped to accept the pedal rod.
The lines were the correct size and it bolted to the firewall with no problems.
I would not recommend.

For a little context, I have 2001 Chevrolet Blazer rear axle and brakes. At this time I have the stock Vega front brakes, combination valve, and all lines.
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