swapping a cast iron master cylinder for an aluminum

[moonrunner1972]

I am considering swapping the cast iron master cylinder on my 1973 Dodge Polara for the newer, later 1970's OEM aluminum style with the plastic reservoir. My Polara came factory with the disc/drum setup so I would imagine all I will need is the adaptor that bolts to the power brake booster. Are their any other things I need to do for the swap? Thanks.

 

[Big_John]

What would be the advantage of doing this?

 

[commando1]

Ditto.
Three times over....

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[thrashingcows]

I have the aluminum one on my wagon. It works well....maybe too well! With the power assist I barely have to touch the pedal to get the brakes to apply. So much so that the brake lights don't always come on....I did not realize this until this year while on vacation.

I don't know if the issue lies with the MC I'm using, or if the MC with it's bigger cylinder bore, and the possible over assisting of the brake booster, is just applying too much line pressure?

This is one of the main reasons I want to go to manual brakes...but still keep the aluminum MC.

 

[commando1]

So they are that much better?? I never gave that a thought until now if what you say is true.

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[bluefury361]

I have the aluminum one on my wagon. It works well....maybe too well! With the power assist I barely have to touch the pedal to get the brakes to apply. So much so that the brake lights don't always come on....I did not realize this until this year while on vacation.

I don't know if the issue lies with the MC I'm using, or if the MC with it's bigger cylinder bore, and the possible over assisting of the brake booster, is just applying too much line pressure?

It could be that the pushrod is to long.

 

[moonrunner1972]

I always assumed the aluminum body and the plastic reservoir were better at dissipating heat. I am guessing that any benefits would hardly be worth the effort?

 

[Badvert65]

All things equal, main thing is saving about 10 pounds of weight (based on comparing the 76 Volare cast iron unit to the 79 Volare aluminum/plastic one).

 

[commando1]

All things equal, main thing is saving about 10 pounds of weight (based on comparing the 76 Volare cast iron unit to the 79 Volare aluminum/plastic one).

10 pounds? In a C-body??
And I can lose ten pounds just by the gas I use driving twenty miles.
Not an issue.

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[68Bigred]

I like to jump in on this one...I have the early 70's MC on my car because I swapped to 4w disc. Althought the brakes are a ton better then the drums I've felt I wished they were more powerful. I was told to go to a new style one that uses just 2 bolts to mount to the PB booster as they supply MORE line pressure not less. Smaller bore higher line pressure I was told. Is what I am being told wrong? If the smaller bore one does work I also want to do the swap. Summit has the adapter kit to mount 2 hole MC to 4 stud PB booster.

Thrashingcows...What is ithe MC you are using???

 

[67Monaco]

So they are that much better?? I never gave that a thought until now if what you say is true.

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Technology, it's not just voodoo anymore...

 

[moonrunner1972]

So back to my original question....aside from the adapter, are their any other pieces that need to be changed to make the swap complete???

 

[bluefury361]

Smaller bore higher line pressure I was told. Is what I am being told wrong?QUOTE]


I think so. I'm working on a build now that has Wilwood 4 wheel disc's. I'm using 4 piston calipers with 12" discs. I didn't want to use a power booster because of restricted space .... plus they are just ugly to look at. Wilwood suggusted their 1" bore master cylinder. Pedal effort is minumal with plenty of line pressure.

 

[Fishfan]

I like to jump in on this one...I have the early 70's MC on my car because I swapped to 4w disc. Althought the brakes are a ton better then the drums I've felt I wished they were more powerful. I was told to go to a new style one that uses just 2 bolts to mount to the PB booster as they supply MORE line pressure not less. Smaller bore higher line pressure I was told. Is what I am being told wrong? If the smaller bore one does work I also want to do the swap. Summit has the adapter kit to mount 2 hole MC to 4 stud PB booster.

Thrashingcows...What is ithe MC you are using???

If it works like humans work then smaller bore does equal more pressure. Plaque in your arteries makes them have a smaller bore and drives up your blood pressure. Put your thumb on a garden hose and see this in practice.

 

[Big_John]

Smaller piston equals higher pressure, but more movement. The piston has a smaller area and the same pressure (your foot) is applied. Example: a 1 inch diameter piston is .785 square inches. A 1.25 diameter piston is 1.227 square inches. Let's say you apply 100 pounds of force with your foot. 100lbs/.785sqin=127 PSI. 100lbs/1.227sqin=81 PSI. There's more force, but you have to push the pedal just a touch farther to push the same amount of fluid.

Back to the original question... You'll need to match the bore size of your existing master cylinder to keep the force the same... or figure out what the desired size is for whatever brake mods you are doing. Then you need to make sure the push rod length will work out. There are adjustable rods out there. Then you have to mount the new master which will mean an adapter.

I still really don't see any advantage to making the change unless you are doing a lot of other mods to the brake system. But that's just my opinion.

 

[commando1]

So they are that much better?? I never gave that a thought until now if what you say is true.

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Technology, it's not just voodoo anymore...

There is zero technology advances from the late 60's to the present.
Push piston to compress fluid to exert pressure...

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[commando1]

I did a lot of work with early 2000's M/Cs for another project. There was zero difference in principles and application. In fact, I found that they had much less possibility of having a normal service life. Yes, they wore junkier in quality. OEM is what I believe in.

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[thrashingcows]

It could be that the pushrod is to long.

I have messed with everything in the system to try and dial it in. Nothing seems to make the braking "normal".

 

[commando1]

Your pedal travel length is totally wrong.
There are formulas to calculate the exact pedal travel length based on a bunch of M/C parameters.

M money is on that the M/C is fine but you didn't change your throw.

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