Master Cylinder???

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mopowers

mopowers

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I'm converting the drums on my 68 to later model A-body discs. Do I need to swap the master cylinder as well? If so, which one do I get. It seems there are a million different brands/ bore diameters/ reman. vs. new, etc... out there
 
I converted mine from drum to disc (manual) and i think the master varies in the fact of the size of the brakes and the power or manual factor.
 
I believe that would work, but you need the prop valve from the donor car, or an adjustable one.
 
I've always used a manual for a "75 plymouth valiant" on 3 different conversions. 1 factory and 2 scarebird. Bolts on with the same 4 bolt pattern and uses your same pushrod. The only mods may be for you lines. I plumb the fronts straight to the big reservoir and an adjustable prop valve inline to the backs to adjust bias.
 
Valiantsignet20 said:
I've always used a manual for a "75 plymouth valiant" on 3 different conversions. 1 factory and 2 scarebird. Bolts on with the same 4 bolt pattern and uses your same pushrod. The only mods may be for you lines. I plumb the fronts straight to the big reservoir and an adjustable prop valve inline to the backs to adjust bias.
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So, you just ditch the factory prop valve and 'T' the front line. Then just use an adjustable prop valve for the rears? Seems easier than buying the 'correct' proportioning/distribution valve. I can't seem to find those for any less than $100 anyway. Do you know a good source for them, before I pop for an adjustable one from summit???
 
Yeah, I use the drum brake block for a T. Leave the front lines connected and cap the rear line outlet. Run new line from you adj. valve to the existing rear line. I have got adj valves from pirate jacks on ebay for $25.
 
Valiantsignet20 said:
Yeah, I use the drum brake block for a T. Leave the front lines connected and cap the rear line outlet. Run new line from you adj. valve to the existing rear line. I have got adj valves from pirate jacks on ebay for $25.
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Do you happen to have a link for the adj. valve you are using?? Have you had any problems with it?
 
No I don't have a link. It is just a valve. Just like a water spigot. I have used mopar, summit and the pirate jack one. They all are the same design and probably the same manufacture. You pay more for the name etched on it. Just do a search for Adjustable Proportioning Valve and look for the cheapest.
 
Valiantsignet20 said:
No I don't have a link. It is just a valve. Just like a water spigot. I have used mopar, summit and the pirate jack one. They all are the same design and probably the same manufacture. You pay more for the name etched on it. Just do a search for Adjustable Proportioning Valve and look for the cheapest.
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Thanks I found the one I'm looking for.

http://www.ebay.com/itm/Adjustable-...674&pid=100015&prg=1006&rk=1&sd=160938822999&


That'll save me $50. Thanks!
 
The "several things" about master cylinders

Drum master cylinders traditionally used "residual pressure" valves. These maintain a small pressure in the system, so that when the pedal is released, air cannot pass the wheel cylinder cups before the return springs can react.

Disc systems do not use these. This means that you may have a master with the drum half of the outlet having a residual valve, the disc section will not

Size, of course. Bigger means more pedal effort, moves the pistons/ cylinders further

Recess for the pushrod. It is imperative that the mechanical travel of the piston be complete or it will "hold" pressure which can lock up the brakes. So manual / power, or different makes or models means that the recess in the rear piston is different and needs to be addressed.

Too deep a recess, especially with a booster, costs you usable movement, and too shallow means the cylinder won't work correctly and neither may the booster.
 
I'm going from manual drums to manual discs, so the recess should be the same, right?

After a little research, the bore diameter for a manual drum/drum car looks to be 1", whereas the bore diameter for a manual disc/drum car seems to be 1 1/32". Is that enough of a Difference to worry about??

So, it looks like my only hang up should be the residual valve in the master. Is it bad to run a front disc brake system with a master with a residual valve?
 
There is no "factory prop valve" on a drum/drum car.

There IS a "distribution block" or "safety switch" (same thing).

You just leave that in place and plumb a prop valve into the rear line, beyond the block.

mopowers said:
So, you just ditch the factory prop valve and 'T' the front line. Then just use an adjustable prop valve for the rears? Seems easier than buying the 'correct' proportioning/distribution valve. I can't seem to find those for any less than $100 anyway. Do you know a good source for them, before I pop for an adjustable one from summit???
Click to expand...
 
DO NOT use your drum/drum MC. The residual pressure valve will cause the disks to drag and overheat. Even if you remove the valve, the drum MC has a much smaller reservoir for the front line, and you may need the capacity of the disk MC.

For a manual disk/drum setup, use the POWER disk brake MC listed for A-bodies. This will have the smaller 15/16" bore and give reasonable pedal effort. If you're feeling macho, you can use the MANUAL disk MC, with a 1-1/32 bore -- this gives a very stiff pedal requiring about, oh, 180-200lbs of foot pressure.

BTW, do not trust the on-line application listings for MCs on Rock Auto or NAPA, etc. They contain a lot of mistakes and misinformation, particularly for cars earlier than 1972. For instance, for a 1967 Barracuda, they will show the drum/drum MC for disk brake applications, if they show a disk brake option at all. So be sure to read the specs -- don't just order based on the application.




mopowers said:
I'm going from manual drums to manual discs, so the recess should be the same, right?

After a little research, the bore diameter for a manual drum/drum car looks to be 1", whereas the bore diameter for a manual disc/drum car seems to be 1 1/32". Is that enough of a Difference to worry about??

So, it looks like my only hang up should be the residual valve in the master. Is it bad to run a front disc brake system with a master with a residual valve?
Click to expand...
 
mvh said:
DO NOT use your drum/drum MC. The residual pressure valve will cause the disks to drag and overheat. Even if you remove the valve, the drum MC has a much smaller reservoir for the front line, and you may need the capacity of the disk MC.

For a manual disk/drum setup, use the POWER disk brake MC listed for A-bodies. This will have the smaller 15/16" bore and give reasonable pedal effort. If you're feeling macho, you can use the MANUAL disk MC, with a 1-1/32 bore -- this gives a very stiff pedal requiring about, oh, 180-200lbs of foot pressure.

BTW, do not trust the on-line application listings for MCs on Rock Auto or NAPA, etc. They contain a lot of mistakes and misinformation, particularly for cars earlier than 1972. For instance, for a 1967 Barracuda, they will show the drum/drum MC for disk brake applications, if they show a disk brake option at all. So be sure to read the specs -- don't just order based on the application.
Click to expand...

Thank you! Thats good to know! I'll go ahead and pick up a Power disc/drum master for a 74 Dart. Are the cheap Reman. Cardone ones any good???
 
I was just talking to Bill Reilly today, (he makes the AlterKation front suspension I just bought) I'm going with front discs on my alterkation and he said for manual brakes use a smaller diameter bore size master cylinder to get the PSI you need. 15/16" or 7/8" bore. He suggested a 73 Dart manual disc/drum application like mentioned above. It's supposed to be a 15/16" bore.
 
any of the factory masters will suck. spend a few extra bucks over the factory junk and call Dr Diff and get one of his late model ones. smaller unit and works awsome for big brakes. your prop valve should work fine. i am running 6 piston wilwood front and Dr Diff"s rear cobra kit and it is amazing. he is the man on info for brakes. call him,you will thank me later.

View attachment DSC03028.JPG
 
wracks71 said:
any of the factory masters will suck. spend a few extra bucks over the factory junk and call Dr Diff and get one of his late model ones. smaller unit and works awsome for big brakes. your prop valve should work fine. i am running 6 piston wilwood front and Dr Diff"s rear cobra kit and it is amazing. he is the man on info for brakes. call him,you will thank me later.

View attachment 1714572153
Click to expand...

Define "a few extra bucks." I would need an adapter and one of those fancy aluminum masters. How much does all that cost???? Is the difference THAT important?? I just wanna DRIVE my car.
 
Valiantsignet20 said:
Yeah, I use the drum brake block for a T. Leave the front lines connected and cap the rear line outlet. Run new line from you adj. valve to the existing rear line. I have got adj valves from pirate jacks on ebay for $25.
Click to expand...

I did the same on my 64 & 65. Recently got an adj prop valve w/ Jegs logo off ebay for $28, same Chinese factory. The plug is "3/16 male inverted flare" in bubble packs at Autozone. Ditto for the 1/4 to 3/16 adapter us early A guys need.
 
mopowers said:
Define "a few extra bucks." I would need an adapter and one of those fancy aluminum masters. How much does all that cost???? Is the difference THAT important?? I just wanna DRIVE my car.
Click to expand...

i can understand that. i THINK it was like $160 or something. but if you ever upgraded,you have it.
 
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