Brake Master Cylinder Swap.

[wnagel]

I have a question, I would like to import some brake parts, My car come with the straight master cylinder ,picture "orig" ( see attach), but I would like to use the most modern master cylinder "step bore master cylinder" , picture "orig2", my car are 1978 , It is possible to remove the original master cylinder and put the most modern without change the brake lines, pipes or servo?

Thanks a lot.


Waldo.

 

[pontiacgp]

the picture isn't always correct but if you search for a master cylinder for a 1978 Cutlass it shows the new cylinder you want to get...Clutch has the same car you have so maybe he has some info that could help you...

http://www.partsgeek.com/ymm/1978/oldsmobile/cutlass.html?category=brake&part=brake_master_cylinder

 

[wnagel]

My car come with straight old style master cyllinder, when I search in rock auto , its offer a old and new style....here in Chile, I can buy only a new style.... thanks pontiacgp !

 

[Monte Cristo]

It is possible to remove the original master cylinder and put the most modern without change the brake lines, pipes or servo?
.

If the new m/c has the same size fittings, yes you can do this, meaning they will bolt up. Will it work properly? That is the real question. You need to be very careful that piston in the new m/c is the same size or bigger than the old one. Otherwise, the pedal will need to travel further to move the wheel cylinder pistons to activate the brakes. You also should measure the pedal travel with the new linkage. I recommend that you consult Fred Puhn's book, Brake Handbook, if you are modifying your brake system.

A newer translucent reservoir on the top of the m/c is better since you can read the fluid level without opening the system. Opening the reservoir allows moisture into the system where it might dissolve in old brake fluid and boil during an emergency stop causing the brakes to fail.

 

[wnagel]

If the new m/c has the same size fittings, yes you can do this, meaning they will bolt up. Will it work properly? That is the real question. You need to be very careful that piston in the new m/c is the same size or bigger than the old one. Otherwise, the pedal will need to travel further to move the wheel cylinder pistons to activate the brakes. You also should measure the pedal travel with the new linkage. I recommend that you consult Fred Puhn's book, Brake Handbook, if you are modifying your brake system.

A newer translucent reservoir on the top of the m/c is better since you can read the fluid level without opening the system. Opening the reservoir allows moisture into the system where it might dissolve in old brake fluid and boil during an emergency stop causing the brakes to fail.

Hi,

Its a good point, the original master cylinder is a 1" bore and new style is 15/16 " bore, but the rear cylinder,( from drums), are the same in all years, brake booster and caliper are the same too , I pressume new style, ( step bore) are more powerfull than the original straigh bore master cylinder.....

Waldo.

 

[pontiacgp]

If the new m/c has the same size fittings, yes you can do this, meaning they will bolt up. Will it work properly? That is the real question. You need to be very careful that piston in the new m/c is the same size or bigger than the old one. Otherwise, the pedal will need to travel further to move the wheel cylinder pistons to activate the brakes. You also should measure the pedal travel with the new linkage. I recommend that you consult Fred Puhn's book, Brake Handbook, if you are modifying your brake system.

A newer translucent reservoir on the top of the m/c is better since you can read the fluid level without opening the system. Opening the reservoir allows moisture into the system where it might dissolve in old brake fluid and boil during an emergency stop causing the brakes to fail.

I agree with your points but the master cylinder he is looking at is the recommended replacement for his car

 

[wnagel]

I agree with your points but the master cylinder he is looking at is the recommended replacement for his car

I pressume that , only in 1978 olds use this straight master cylinder...1979+ use step bore...

 

[Monte Cristo]

Hi,
Its a good point, the original master cylinder is a 1" bore and new style is 15/16 " bore, but the rear cylinder,( from drums), are the same in all years, brake booster and caliper are the same too , I pressume new style, ( step bore) are more powerfull than the original straigh bore master cylinder.....
Waldo.

The problem here is that calipers are not actually the same on a system designed with the "quick take up master cylinder". That was its official name in GM's 1981 patent application: http://www.freepatentsonline.com/4445334.pdf
It is also known as a "fast fill" or "step bore". It was designed to reduce drag by keeping the calipers further away from the rotors and thus improve gas mileage. With the older model, the calipers are closer to the rotors and will clatter against them without applying the brake pedal. The m/c and caliper wheel cylinders are designed specifically to work together. The m/c in this system starts with more pressure, and the at a point specified by the wheel cylinders' design, it is reduced. Because of that, mixing and matching a m/c with calipers designed for the other system causes problems without the benefits of the system that it was designed to operate. There is also a problem with aftermarket calipers that were rebuilt from cores indiscriminately with the wrong seals reinstalled in the seal groves, or having one type of caliper on one side of the car, and the opposite type on the other: http://www.remaninc.com/pdfs/lowdragcalipers.pdf

So, at a minimum, be sure that the m/c and the front calipers are intended for the same design on this car. (I omit the rear because both original and modified are/were drum, but otherwise would include the rear too.) Any kind of change in the brake hydraulics is a kind of reengineering of the original system that should require much thought, and if undertaken, sufficient road testing and comparison to be sure the system operates at least as good as stock. It requires more than just mixing and matching hydraulic system parts. See this warning here:
"Re-Engineering your brake system is a dangerous thing to undertake, DO SO AT YOUR OWN RISK! NONE OF THE ABOVE IS APPROVED BY ANY MANUFACTURER, I AM NOT AN ENGINEER. David"
http://www.pozziracing.com/quick_take_up_master_cyl.htm

I agree with your points but the master cylinder he is looking at is the recommended replacement for his car

What is recommended by one vendor is what they are selling, and not necessarily what is needed, or best, for the car.

 

[wnagel]

Okey I understand, In this case Its more safe to obtain a caliper from 1979+ who come with step bore master cylinder? respect to rear drum brake, I see in parts wharehouse the cylinder are the same in all years.....

Monte cristo thanks a lot!

 

[pontiacgp]

The problem here is that calipers are not actually the same on a system designed with the "quick take up master cylinder". That was its official name in GM's 1981 patent application: http://www.freepatentsonline.com/4445334.pdf
It is also known as a "fast fill" or "step bore". It was designed to reduce drag by keeping the calipers further away from the rotors and thus improve gas mileage. With the older model, the calipers are closer to the rotors and will clatter against them without applying the brake pedal. The m/c and caliper wheel cylinders are designed specifically to work together. The m/c in this system starts with more pressure, and the at a point specified by the wheel cylinders' design, it is reduced. Because of that, mixing and matching a m/c with calipers designed for the other system causes problems without the benefits of the system that it was designed to operate. There is also a problem with aftermarket calipers that were rebuilt from cores indiscriminately with the wrong seals reinstalled in the seal groves, or having one type of caliper on one side of the car, and the opposite type on the other: http://www.remaninc.com/pdfs/lowdragcalipers.pdf

So, at a minimum, be sure that the m/c and the front calipers are intended for the same design on this car. (I omit the rear because both original and modified are/were drum, but otherwise would include the rear too.) Any kind of change in the brake hydraulics is a kind of reengineering of the original system that should require much thought, and if undertaken, sufficient road testing and comparison to be sure the system operates at least as good as stock. It requires more than just mixing and matching hydraulic system parts. See this warning here:
"Re-Engineering your brake system is a dangerous thing to undertake, DO SO AT YOUR OWN RISK! NONE OF THE ABOVE IS APPROVED BY ANY MANUFACTURER, I AM NOT AN ENGINEER. David"
http://www.pozziracing.com/quick_take_up_master_cyl.htm



What is recommended by one vendor is what they are selling, and not necessarily what is needed, or best, for the car.

he is not redesigning the brakes, the master was superseded by the master he wants and if you look up the calipers the same caliper was used from 78 up to 87.