Master Cylinder question.

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nodemon

nodemon

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Just received my aftermarket M.C..
Comparing it to my OEM one I noticed an extra, "hole" in the rear brake reservoir.
Can anyone tell me what that extra hole is for and is it necessary. Manual Drum system.

20231124_194617~2.jpg

Aftermarket on left, OEM on right.
 
That after market holes in the picture do not even look drilled let alone have a check ball in them. May be some different pictures to clear this up?
I’ve had factory masters with multiple holes before. No idea what the heck they are for. I’ve rebuilt master cylinders before (when that was all that was available) and brake cleaner just blew thru those holes to the bore area.
 
Syleng1 said:
That after market holes in the picture do not even look drilled let alone have a check ball in them. May be some different pictures to clear this up?
I’ve had factory masters with multiple holes before. No idea what the heck they are for. I’ve rebuilt master cylinders before (when that was all that was available) and brake cleaner just blew thru those holes to the bore area.
Click to expand...
They're drilled through.. not sure about a check ball though..,

20231125_104928.jpg


20231125_104934.jpg
 
I have never seen any chechballs in those ports, and
call me crazy but if I had a M/C with a checkball in there, I would remove it.
Here is a cutaway of a M/C; the firewall is to the right.
Each reservoir has two ports. One port in each reservoir is for to compensate for wear in the friction materials, and the other;
in the case of the rear reservoir, allows fluid into the chamber between the pistons. This inter-piston chamber, after all the ports are closed to it, becomes a hydraulic connection between the two pistons. In normal operation, there is no mechanical connection between the two pistons unless there is a catastrophic loss of pressure on one side of the dual-brake system; which, if it happens, allows the rear piston to slide into the back of the front piston, and thus half the brake system should still function.
I see no point in having a check-ball in any of those ports, that allowed one-way-only fluid travel; and there is only one port that could receive it and the contraption still continue to function properly.
1700934057495.png
 
No checkballs .
Those side by side holes both fill the void behind the 1st chamber seal.
Might be considered a "performance feature" lol
 
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Yes but think of the picture shown above. The first hole fills the cavity then as the piston compresses the check valve is covered to compress. The piston needs to be all the way back for the fluid to get pushed back into the reservoir on the return stroke. Just saying. Fluid control. Once on the backside of the piston would lock it forward and not able to return. Just staring a need for a one way check valve for the return flow.
 
Syleng1 said:
Yes but think of the picture shown above. The first hole fills the cavity then as the piston compresses the check valve is covered to compress. The piston needs to be all the way back for the fluid to get pushed back into the reservoir on the return stroke. Just saying. Fluid control. Once on the backside of the piston would lock it forward and not able to return. Just staring a need for a one way check valve for the return flow.
Click to expand...

@AJ/FormS is spot on.

How many master cylinder’s have you disassembled and rebuilt that had “check balls” in them, and what was the application?

Because like AJ, I have disassembled and rebuilt master cylinders, and I haven’t seen one with a “check ball” in the location that you say needs one. Residual valves on the line exit ports yes, but not a check ball. Certainly not on anything relevant for these cars.
 
Not shown is a series of holes in the piston behind the forward cup, so if the piston is drawn back quicker than fluid can pass the hole, the back of the cup unovers the piston holes, allowing fluid from the void to bypass the cup keeping the forward chamber full.
Hope that makes sense. I spent a while looking for a pic, found lots of what I didn't need . lol
 
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So, there's been some good responses and educational information...but, is there a problem or issue with the new MC not having the "extra hole" that my original has... and, what is that "extra hole" there for..?
 
nodemon said:
So, there's been some good responses and educational information...but, is there a problem or issue with the new MC not having the "extra hole" that my original has... and, what is that "extra hole" there for..?
Click to expand...

I’d use it and not worry about it as long as it bench bleeds ok.

As for the old one, beats me. Could have been an error, cold be there’s a difference in the piston, seals or passages between the old and new one. As long as the new one works I wouldn’t give it a lot of though unless you want to tear them down and compare the internals.
 
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