Is this correct for swapping Master Cylinder from single to dual?

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gdizzle

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I am not getting anywhere with my research on this topic. in my 66 dart, swapping to disc front, keeping rear drums (9in). When I bought the new Master Cyl Dorman M80266, and I removed the original MC and I reused the original Push rod. I simply pulled it out. However I also have the original spring and booty that can not be properly installed onto the new MC. See my pic of what I have done and let me know if I am supposed to still use this spring, or is it not needed with this new MC. You can see the thing on the ground is what is supposed to hold the spring from the old MC.
IMG_3700 2.jpg
 
So why don't you drill two holes where they belong 1/4 in or even a little smaller and tap them so you can screw the original part on ? Seems like a simple enough thing to do to have it right.You know these Chinese parts like Centric and Dorman cut corners like leaving those holes out.
 
You really don't need the boot or the spring, or that plate. The boot just keeps dirt out, but unless you're driving off road a lot I can't see all that much dirt getting in there. The spring is a return spring, but on the later master cylinder a version of that spring is inside. One word of warning, you may need an adjustable push rod to get your pedal height in the correct place.
 
I have never seen seals "killed" by lack of rubber boot.
They put it there for a reason and drilling two little holes and running a tap thru them so the mount for the boot can be attached seems like a smart thing to do to me and I'd want it on my car just because of that .But , hey,to each his own.
 
Are you saying the spring is not needed? It does feel like when I push brake it takes too far before braking begins. And as I let it up I can feel toward the end, that something changes and the pedal keeps coming up. Is it possible that this spring is pushing the pedal too hi? It is a major issue for me. I've even ordered another MC to see if it is any different. Do the adjustable rods all fit this type of MC? Any links would be greatly appreciated.
 
The spring isn't attached to anything, is it? Far as I know on later cars the only "return spring" is inside the M/C. If your pedal is too high it sounds as if you need an adjustable push rod. Putting a newer model M/C on a '66 car is not something I've personally done, but I always thought '66-'72 were all mostly the same. So I'd say contact Dr. Diff... he probably knows more about this than anyone else around here. Mopar '62 -'70 Adjustable Master Cylinder Push Rod
 
I have never come across this but that don't stop me from having ideas.
If the spring is not attached to the pushrod then it is not doing anything. If the original pushrod had a method to anchor the spring, then it was a pedal return spring. As others have said, the dual M/C has the pedal return spring inside of it. As mentioned, the pushrod has to be the right length to park the pedal high-enough so that during use it will brake without hitting the floor.
However, the pedal also has to be up high enough that if a brake-line ruptures, on one end of the car or the other, that the safety system still works. And finally, it has to be up high enough that you can't put your toe under it and yank the pushrod out of the back of the M/C
But it cannot be so long as to prevent the compensating port from opening inside the M.C. When this happens, the pedal sinks lower and lower over time, eventually running out of brake travel inside the M/C. Most of the first inch of pedal travel gets used up closing the compensating port, before any braking action occurs, and this is normal.
Usually the pushrod is anchored inside the socket and it's a really good idea to have it working that way, cuz if it slips outta that socket it's bye-bye brakes.
I suspect the unusual thing you are feeling is probably the pushrod slipping back into the socket.
Don't forget, the large reservoir goes to the discs.
If the pedal forces it's way back up, then you probably have either boiling/contaminated fluid, in the calipers; or air in the system( front or rear). Disc brakes need disc-brake fluid which has a higher boiling point than drum fluid. All of the old fluid has to come out, or it will reduce the effectiveness of the new fluid... plus the old fluid may already be a large enough percentage water, that it is already long past it's best-before date.That's a joke, eh. Brake fluid is hydroscopic, which means it attracts water like a magnet attracts iron. Use only fluid from a sealed container, and that means SEALED.
 
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I have never come across this but that don't stop me from having ideas.
If the spring is not attached to the pushrod then it is not doing anything. If the original pushrod had a method to anchor the spring, then it was a pedal return spring. As others have said, the dual M/C has the pedal return spring inside of it. As mentioned, the pushrod has to be the right length to park the pedal high-enough so that during use it will brake without hitting the floor.
However, the pedal also has to be up high enough that if a brake-line ruptures, on one end of the car or te other, that the safety system still works. And finally, it has to be up high enough that you can't put your toe under it and yank the pushrod out of the back of the M/C
But it cannot be so long as to prevent the compensating port from opening inside the M.C. When this happens, the pedal sinks lower and lower over time, eventually running out of brake travel inside the M/C..
Usually the pushrod is anchored inside the socket and it's a really good idea to have it working that way, cuz if it slips outta that socket it's bye-bye brakes.
I suspect the unusual thing you are feeling is probably the pushrod slipping back into the socket.
Don't forget, the large reservoir goes to the discs.
If the pedal forces it's way back up, then you probably have either boiling/contaminated fluid, in the calipers; or air in the system.
Also has to be at the correct height for the brake light switch to work. If that's not working right, something is really out of whack.
 
The spring is attached to the push rod with that flat washer like clip that fits into a grove on the rod at the proper height. I use silicon fluid in all my brake systems both drum and disc .It doesn't absorb H2O from the atmosphere like dot 3 or 4
 
If the pushrod is not anchored in the M/C socket, then I would not use that external return spring, cuz IMO that's just asking for trouble;
Unless your pedal is so darn heavy that the internal one can't keep it up.
But then I would make darn sure the pushrod cannot come out of the socket.
As to the silicon fluid, it still has to be pure to be effective. I use it too.

Hang on, I see that there may not be any way for the pushrod to jump out of the socket if the spring-hat was properly screwed to the back of the M/C. If that's right, then it should all work correctly, once screwed together, so long as the C-ports are open when the pedal is parked.
I may have been a lil hasty, sorry.
That just leaves the rising pedal, which is not normal. Especially not with disc brakes. Generally, on casual stops,the nearer the car is to becoming stopped, the more pedal has to be applied, until just before the final foot or inches. This is just the opposite of drum brakes which are self-energizing.
For the pedal to force it's way back up, under your foot, I see only two scenarios; 1) the piston is being forced back into the caliper; and I see no mechanical way for that to take place,or 2) the brakefluid is expanding.
Ok there is a third possibility; if the rotor is so thin it can't get rid of the heat and it is physically expanding between the pads. But your front rotors should be ventilated .....right...which would preclude that.
That's all I got.
 
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