70 LS1

Can you install a power brake master cylinder on a manual brake car? I am not looking to convert to power brakes. I just want a master cylinder with a larger bore.

thanks

norvalwilhelm

The larger bore will cause less pressure for the same pedal effort. Sure you will move more fluid but at a cost of braking power. While it will bolt in the rod might not be the same. The piston in the back of the cylinder I think is deeper with the non power brakes. Don't know this for sure.

70 LS1

This sounds backwards to me. Can you explain where I am wrong? If you move more fluid for the same pedal movement, then wouldn't your line pressure be higher for the same pedal movement?

redvetracr

You can but it will be very difficult (trust me) to push the pedal.....
.....redvetracr

gerry72

The primary pushrod bore depth is exactly the same for power and manual brakes. The difference I believe you are referring to is the 77 and later master cylinder, which uses a shallow piston hole.

You can use a power cylinder but your pedal effort will be a bit higher for the same system pressure. This is because the power piston is 1.125" and the manual is 1.0" in diameter. So this is one of those: Just because you can do it doesn't mean it's a good idea.

And, no, this is not backward. Has to do with piston area. Think about the PSI as pushing on both ends of the hydraulic system. The bigger the piston in either the master or the caliper(or both), the more of the "inch" there is for the PSI to push on.

stingry

I did this as a interim step before installing the booster. I lasted about 3 weeks. The pedal was so hard it was ridiculous. Sure the brakes work but you have to really apply a continuous pressure on them to stop.

I spent $15 on a non-power master cylinder while I waited to get all the pieces I needed to install the booster and the power master cylinder.

70 LS1

I think I understand what you are saying, but.

I am thinking of this as a sealed system where by you are reducing the volume. With a small bore you will lower the volume by a specific amount per inch of movement. With a larger bore you lower the volume by a larger amount per inch of movement. Wouldn't this cause pressure to be greater in the system?

Now lets say you went to larger pistons in your calipers. Wouldn't you want a larger bore to compensate for the larger pistons?

stingry

70LS1,

Read this.

http://www.mpbrakes.com/mpfaqmasters.htm

It gives some good explanations.

Pete

70 LS1

thanks

70 LS1

So it looks like I need a smaller master cylinder bore instead of a larger one. I was ultimately looking to increase line pressure and reduce pedal effort.

redvetracr

Not to confuse the situation but in the Corvette section of the (older) Chevy power book they talk about a 1.250" truck master for use WITH a booster............it works
.....redvetracr

70 LS1

Ok, I think I have this all figured out.

By going to larger pistons in the calipers, you would require a smaller master cylinder bore to get the same line pressure to actually increase your braking. This explains why my pedal effort was more with the C5 calipers and the stock 1" master cylinder. The C5 calipers are 2 piston calipers which was throwing me off at first.

After breaking out the ol physics book and doing some calculations, it shouldn't matter if they are 2 piston floating or 4 piston fixed due to the design.

With the same line pressure and the same piston diameter the pistons will exert the same force onto the pad regardless if 2 or 4 piston. This is because the pressure pushing the piston is also pushing back on the sliding caliper applying force to the other pad.

The C5 pistons are larger than the C3 pistons meaning the C5 calipers would give more clamping power for the same line pressure.

Looks like I need to find a 7/8" master cylinder.

427V8

What is the diameter of the C5 piston?

A C3 has 1.875" piston is front giving 5.519 in2 of piston area.

an equiv single piston would be 2.65" in diameter.

69autoXr

Any idea what year truck master?

LemansBlue68

My '68 had a power master cylinder on it from the factory and was an original manual brake car. It had never been replaced as far as I could tell. Correct bleeder screws, correct date, correct number (for power brakes).... The power brake master is 1 1/8" bore the manual is 1" bore.

The best I can figure, it was installed by mistake or the line was short of manual cylinders so a power M/C was installed. Neither me or the previous owner ever knew different until I started the restoration.

I installed power brake booster and lines and rebuilt the master cylinder during the restoration.

redvetracr

[QUOTE=69autoXr]Any idea what year truck master?[/QUOT


Sure!! 74-75 20&30 series Chevy trucks, you should also know you will probably need to "slot" the mounting holes and remove the pressure reserve valve from the rear circuit.
.....redvetracr

70 LS1

From a reliable source ( I didn't feel like taking mine apart to measure them) the fronts are 1 9/16 and the rears are 1.75. That seems small to me, but the source is reliable. If I get ambitious I will pull on of the calipers off and measure them.

gunshp

What Master did you use when you were racing? I am using a stock manual and get a lot of knockback

kodpkd

I also had a larger master cylinder bore on a manual car. My brakes weren't worth a darn. It took a while to figure it out. When I went to the 1 inch bore, my brakes improved a lot. I also changed from stock organic pads to HAWK HPS pads, another big improvement. Bench bleeding the calipers also made a huge improvement. This is on a 68.

vettebuyer6369

You are responding to a 15 year old post.