Master Cylinder Internal Arrangement Question

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I8NEMO

I8NEMO

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This is a RSD-DBMC10 I got from Summit. I bench bled it months ago with DOT 3, All other brake components are new and have never seen brake fluid. Now I have made the decision to go with DOT 5 and am cleaning it out. I coaxed the rear piston out with some air, careful not to eject it across the shop so I'd have orientation, laying in the bottom was the spring and a retainer apart from each other sort of stuck in what I assume is assembly "grease" which is clear/opaque (is it possible this is congealed DOT 3?, never seen anything like it) at the bottom of the bore. I have both pistons oriented correctly in the pic,at least that is how they came out, however the last (first in) spring and retainer are a guess. This retainer does not fit into the end of the spring, it's a little big for the spring opening. Need a little help here with the spring and retainer orientation fellas, could not find Right Stuff Detailing anywhere on-line.

Thanks in advance!

Tim

master cylinder spring pic.jpg
 
What is the closest OEM application for that master? Should be a breakdown "in the book"
 
I think that retainer goes behind the spring like a seat. Does it fit like that? The front one looks like that from here
 
DOT 3 will absorb water but not to the extent of jelling. It could be packing grease.
 
In general you are correct, but I have never seen that white retainer before. Could it fit first on the front piston followed by the spring? In this position it would serve to expand the rubber seal and locate the spring on its small end.
 
Murray said:
In general you are correct, but I have never seen that white retainer before. Could it fit first on the front piston followed by the spring? In this position it would serve to expand the rubber seal and locate the spring on its small end.
Click to expand...

IMG_0116.JPG


IMG_0117.JPG
 
pishta said:
I think that retainer goes behind the spring like a seat. Does it fit like that? The front one looks like that from here
Click to expand...

That's what I thought too, but it doesn't fit in, or around the spring, on either end. It does appear to be the same retainer as on the front piston and Im wondering if it even belongs in there at all.
 
yeah, it looks as if it goes on the spring to center it in bore and prevent contact with wall. See if it fits like that, teeth facing the front spring, first part back into the bore.
 
67Dart273 said:
What is the closest OEM application for that master? Should be a breakdown "in the book"
Click to expand...
Not positive yet, Right Stuff was no help. Summit shows this applicable for my 68 Barracuda, but I've seen other data showing it originates post 73.
 
CFD244 said:
View attachment 1715926816
That spring direction looks correct/ how my spring came out. So the big end of the spring rests against the head of the bore, with no need for any retainer, makes sense. I see the retainer in your pic is smooth, my spacer is toothed on both sides and would cut into the cup if used in this position, and is not a good fit at all. The small end of my spring, over the piston stem, rests against an aluminum face surrounded by the cup so I believe a retainer is not necessary, ?? I can't tell in your pic if it also has the same aluminum face.The head end of the bore is obviously scratched from the toothed retainer that neither fits in or around the big end of the spring, the toothed circumference matches the big circumference of the spring and Mocking it back together has the retainer laying wild in there, tilted. This m.c. is new and it seems like the retainer just doesn't belong in there, it is identical to the retainer in the first piston out of the bore, I think the retainer was in there without the assemblers knowledge, idk . Been looking at many exploded drawings, have not found a drawing of this particular unit yet. Right Stuff was no help, they're a middle man and suggested finding a manual

View attachment 1715926817
Click to expand...
 
Last edited:
Murray said:
In general you are correct, but I have never seen that white retainer before. Could it fit first on the front piston followed by the spring? In this position it would serve to expand the rubber seal and locate the spring on its small end.
Click to expand...
The o.d. of the piston stem is much smaller than the i.d. of the retainer, the small end of the spring however is a great fit over the piston stem
 
Executive decision after looking in service manuals etc. Even though the center hole in the retainer is larger than the piston stem this is how the books show it, like Old Man Mopar has it. I believe the cups gotta have spring tension against it or it would slide forward on each pedal return. After a closer look the teeth on the retainer never actually touch the rubber cup.
So, it's big end of spring in first then retainer then secondary piston, then primary piston. Got it bench bled and back in the car with some make shift nipples

20220517_153044.jpg


20220517_085835.jpg
 
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