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Labrauer

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I am putting scarebird disc brakes on my 48 Plymouth coupe and I have read that some guys do nothing with their master cylinder and they work just fine and others say they had to remove the valve to make them work. My question is how do you know if your valve needs to come out or not?

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number one. the stock valve is about 10PSI and that will create a drag on the calipers and keep the pads against the rotors causing drag, heat and wear.   If removed completely there is the chance that the fluid will drain out of the calipers back to the master as the master is vented and will lose such fluid from the vent hole...vent is a small opening in the corner of the stock below the floor master cylinder fill plug....front caliper that are higher than the master should have a 2 PSI check valve installed to prevent the drain and yet be low enough to allow return of the pistons in the caliper....remember, it is the roll of the cut square ring seal in the piston that pulls the piston off the rotor.....

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So Plymouthy - you are saying that if your caliper is lower than the master cylinder then remove the stock 10PSI valve and everything is hunky-doory?

 

I am thinking about putting discs on mine too...although my stock drums work quite good....the only time I feel that discs would be an improvement would be going down a long mountain grade. I have experienced drum brake fade back in the 60's driving a 64 Buick Special, going down a mountain in Chattanooga. Not fun....Solution? Slow down at the top of the grade, put her up in second, and let her hold back going down, use the brakes sparingly........like diesel trucks do now on steep grades. Quite fun, actually........

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8 minutes ago, Cold Blue said:

So Plymouthy - you are saying that if your caliper is lower than the master cylinder then remove the stock 10PSI valve and everything is hunky-doory?

 

I am thinking about putting discs on mine too...although my stock drums work quite good....the only time I feel that discs would be an improvement would be going down a long mountain grade. I have experienced drum brake fade back in the 60's driving a 64 Buick Special, going down a mountain in Chattanooga. Not fun....Solution? Slow down at the top of the grade, put her up in second, and let her hold back going down, use the brakes sparingly........like diesel trucks do now on steep grades. Quite fun, actually........

You still need  the 10psi valve on the rear drum brakes .

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28 minutes ago, Cold Blue said:

So Plymouthy - you are saying that if your caliper is lower than the master cylinder then remove the stock 10PSI valve and everything is hunky-doory?

 

I am thinking about putting discs on mine too...although my stock drums work quite good....the only time I feel that discs would be an improvement would be going down a long mountain grade. I have experienced drum brake fade back in the 60's driving a 64 Buick Special, going down a mountain in Chattanooga. Not fun....Solution? Slow down at the top of the grade, put her up in second, and let her hold back going down, use the brakes sparingly........like diesel trucks do now on steep grades. Quite fun, actually........

no..I did not say that...the question was  how do I know I need it...answer...by the very change to disc and keeping stock cylinder....I did not address the rears as I probably should have and as justold added, you still need the 10 psi for the rear....in regard to the lower master application you have a stock 10psi built in to master.....as you go to disc this is too much...thus the removal and addition of the 2 for disc and a 10 for the rear fitted inline....

 

some folks have said that they never did this and all is well....well some may still have a bit of air in their lines that is buffering the pressure...I have no knowledge of each individual application and or methods of bleed....I do know what is technically needed and the reason for it.  Each can do as they choose or proceed based on a prior learning curve of the industry.

Edited by Plymouthy Adams
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So what I am getting from this discussion is that I don't have to do anything to the master cylinder at all but I do need to put some kind of 2psi valve on the line that goes to the front disc brakes or am I not reading this right. I am  still not sure how to go about getting this done any suggestions or pictures would be of a great benefit 

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5 minutes ago, Labrauer said:

So what I am getting from this discussion is that I don't have to do anything to the master cylinder at all but I do need to put some kind of 2psi valve on the line that goes to the front disc brakes or am I not reading this right. I am  still not sure how to go about getting this done any suggestions or pictures would be of a great benefit 

 

you read over a few lines if that is what you got out of it all......lol

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When I changed over to Rustyhope’s disc brakes in front and Ford 10” drums in the rear, I noticed some drag on the front brakes. I removed the factory check valve in the master fully expecting to have to install external residual pressure valves but I tried it with none. Been running with no valves for a few years now with no issues. 

 

Stock master, disc fronts, modern 10” drums in rear. 

 

If an issue ever arises, I’ll install 2lb front and 10lb rear residual pressure valves. 

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Thanks guys for the answers you all have given. I took the master down out of the car and took out the rubber cup like item hoping it was the this was the valve you are suppost to remove. Put the master back on the car and filled with fluid pumping slowly till all air seem to be out of master but never got any peddle on the brake, I called napa and they don't have a 2lb pressure valve and nor does auto zone or oryles. does anyone know where I can get one and I am assuming I also will have to put a 10lb one in for the back brakes? 

One other thing is when I took the master out the cap under pressure was leeking (squarting) out fluid is that suppost to happen. i got the master from one of the vendors on the fourm a year ago. The cap is tight.

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It’s the rubber disc looking thing encased in a metal holder closest to the nut on the back of the master. If that’s the one you removed, you should get a pedal even if you end up needing the valves. The next day after sitting, if your first pump goes to the floor and the brakes feel normal after, you need residual pressure valves. I found them on amazon. 

 

Adam

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When I put disc brakes on my truck, I asked the same questions.  the answer I took was to have a master cylinder that matched the newest component, so used a MC from a 98 Cherokee. Brakes are number one (1) priority for me. I've installed disc brakes on my B3B and my '53 Plymouth Suburban. Love the discs.used Rusty Hope both times.

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Hey Labrauer, If you took out anything that looked like a cup, it wont build pressure very well. In Keithb7 second post the valve is what comes out. Also if it is under pressure check the rod adjustment. The piston cup should be centered between the two holes in the bottom of the MC. One is a service port to supply fluid and the other small, small, small hole is the return port. (Relieves the pressure from the bakes back into the MC reservoir)Also most MC's have a breather hole in the side of the MC cap.  Watch the vid it gives a really good explanation of the MC system.

 

Joe Lee

 

 

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  • 2 weeks later...

Ok guys I once again got a little time to work on the disc brake again. I have gotten a 2# pressure valve and a 10# valve on the brake lines and also took out the valve in the master but still have know brakes. I can't seem to get any pedal pressure on the brakes. I can't seem to figure out what i am doing wrong. I have adjusted the rod going to the master from the brake pedal trying to get the rubber cup washer in be tween the two holes on the bottom of the master. it is hard for me to see if this is correct or not but I think it is. any suggestions would be appreciated 

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Plymouth Adams what do you mean what else have I changed in the process. I have not changed the rear brakes, I haven't changed anything except for the entire brake lines from back to front. A while back I changed the back shoes and wheel cylinders and a new master cylinder. I changed the brake rod link to what I thought was right. The front brake hoses were changed to the disc brake caliper.  I have checked for leaks and there were non found in the lines or cylinders. pump the brakes and get no pressure at all. Master is full of fluid and when brake peddle pumped no air bubbles come out of the holes in the master. This should be a simple change but it's turning into a disaster. 

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On 5/13/2019 at 8:57 PM, Labrauer said:

. . . I have adjusted the rod going to the master from the brake pedal trying to get the rubber cup washer in be tween the two holes on the bottom of the master. . .

 

Bad idea. If/when you get your brakes bled you will find that they will lock up on the road almost immediately. When the pedal is released the cup must clear both holes in the master cylinder.

 

On 4/24/2019 at 3:17 PM, Cold Blue said:

I am thinking about putting discs on mine too...although my stock drums work quite good....the only time I feel that discs would be an improvement would be going down a long mountain grade. I have experienced drum brake fade back in the 60's driving a 64 Buick Special, going down a mountain in Chattanooga. Not fun....Solution? Slow down at the top of the grade, put her up in second, and let her hold back going down, use the brakes sparingly........like diesel trucks do now on steep grades. Quite fun, actually........

 

The reason my father avoided automatic transmissions for decades was so that he could get compression braking on mountain roads.

 

I was on a Chrysler club tour back around 2000 where we headed down the back side of Mt. Hamilton on a very steep and long down grade. Even with the tiny drum brakes in my '33 Plymouth I was fine. Just kept it in 2nd. The car behind me, a late 1950s DeSoto with an automatic transmission, started overheating his brakes. Fortunately he managed to get it stopped before ramming me and the whole caravan of cars had to wait until his brakes cooled down.

 

Again, just this last March my wife and I took the '33 to car camp in the desert. The downgrade from Julian to Anza Borrego loses about 2000 feet in maybe 8 or so miles on a very curvy road. No problem even with a full loaded car: Just downshift as needed and keep it slow using the brakes only for fine adjustment of speed.

 

If I had an automatic transmission that prevented me being able to use engine compression for braking, I'd seriously consider switching to disc brakes. But with a manual transmission drums are fine on long downgrades. You just have to drive it differently than a new car which is fine by me.

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