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Discussion Starter #1
Hi,
My question is twofold,
1. I want to put a twin reservoir master cylinder I already have, onto a vehicle that currently has a single reservoir master with 4 drum manual brake system. How can I tell if the master I have, which has no identifying marks telling me what it is, is for manual or power drum brakes or manual disc or power disc brakes?
2. If it is for manual or power drum/disc brakes, can I still use it on the 4 manual drum brake system?
Any input is greatly appreciated.


Steve
 

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A drum / drum master cylinder should have rubber check valved behind both brass seats where the brake lines screw in. You should be able to "feel" them if you push the back side of a small drill bit into the center of the hole. A disc / drum master cylinder will only have the check valve behind one of those brass seats. As far as will it work, I'd suggest you stay with a master cylinder that has very close to the the same size piston as your old single m cyl has.

Be certain that both m cylinders have the same depth hole where the push rod goes in the back of the piston. A difference there can be a life and death matter.
 
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Discussion Starter #3
Thanks Jon,
Can I see the check valve(s) or only feel for it? What hole am I putting the drill bit in to? Where the brake line(s) go? What am I feeling for? How do I determine the piston size each master cylinder has, in other words, how do I measure them.
Sorry for all the questions. Want to make sure I'm understanding you correctly.

Steve
 

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The check valves are black. You may be able to see them if you have very good eyesight and a really bright flashlight. As to the feel, they will feel slightly squishy. You don't need to apply lots of force. No more than pushing your finger into your arm. It should be easily noticeable. The hole you put the drill bit in is in the center of the brass seat. As far as measurement, you measure across the opening where the piston is in the rear of the master cylinder. And for the depth of the hole in the piston, any difference should be readily noticeable to the naked eye. I just don't want you to have the push rod drop out of the piston and leave you with no brakes when you are going 60 miles per hour. I know of cases where that happened, and the results weren't pretty.

Pictures would help. Also knowing the car involved, and whether it is power brakes or not would also be helpful. I'm taking it that it is 1966 or earlier or you would already have a dual master cylinder.
 

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Discussion Starter #5
Thanks again Jon,
Sorry for delay in responding, I don't get too much computer time.
I'm now clear on what you are saying.
It's a 1966 C10 pick up truck with manual drum brakes on all four wheels, no pics yet.
Would I be better off getting a dual MC off a 67 manual drum brake C10?

Steve
 

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The master cyl needs to have close to a 1" deep hole where the pushrod goes, so it won't fall out if the pedal returns faster than the piston. The brake line port has a brass seat, behind the seat is a piece of rubber the size of an eraser. The front port needs to have this too. Disc brake systems don't have it. Usually a seal rebuild kit will have them. They are replaced by removing the pressed in brass seat. Thread a screw into the hole in the seat and pry out on the head of the screw. I have a pair of vise grips that I screwed a long bolt into the handle where the adjuster goes. I have a sliding weight on the bolt that I use as a slide hammer.
 

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^^^^ What David said. He really knows his brakes. :thumbsup:

Would I be better off getting a dual MC off a 67 manual drum brake C10?

Steve

I'd say that looks like a good place to start. I looked at pictures on Rock Auto and they seem to mount the same. Like I said before, be real sure the push rod goes deep into the piston. You don't want a master cylinder made for power brakes because normally they don't have the deep hole made to retain the push rod in the piston. While you are buying the master cylinder, also pick up a pair of brake lines that will thread into the master cylinder. Front hole has different size threads than the back hole. No doubt this has been done thousands of times before. You can do it!
 

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Discussion Starter #8
Hi David,
nothing behind seat that I can feel. 1/8th drill bit went right in, no obstruction in both ports.
What size screw? #8 drywall screw work? if you need a slide hammer I take it they are hard to remove, correct?
1-1/2" deep hole where push rod goes. 1/2 dia hole inside, 1-1/2 dia outside.

Steve
 

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Discussion Starter #9
Thanks Jon and David for some excellent insight and sharing your knowledge.
Much appreciated.
P.S. I ordered a new M/C.

Steve
 

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The 1967 C10 master cylinder should have a 1 inch bore, the same as the 66 original master cylinder. The master cylinder you have in hand had 1 1/2 inch bore? Likely that would have given you a rock hard pedal. Not good. The one you ordered should work out fine, as long as the firewall bolt pattern matches, which I believe it will.
 

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Discussion Starter #11
When talking about bore, is that the depth of the hole at back of mc? If so, then what is the dia of bore indicate? Will the push rod be the same on the 67 as the 66 and what clearances (play) should I have if any?

Steve
 

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The bore is the outside diameter of the piston that goes into the casting. The one you have coming should be 1 inch, same as the one on your truck now. Can't say whether the push rod will work as is or not. Best thing to do is measure the depth on the old one when you remove it and then measure the new one. Some push rods are adjustable (slightly) for length. If it isn't, making a new one isn't really too big of a deal. You don't want the push rod to be absolutely bottomed out in the piston either. Maybe 20 thousands or so from it, but not completely bottomed out. If it is, the piston won't return fully and that will keep pressure in the system and make the brakes perpetually drag.
 
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