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Discussion Starter #1
So....my MC went out and I went to buy a new one..

It is much smaller than the old one which was NOT original...
Not only is it a lot smaller but the reservoirs are the same size unlike the old one which had a larger reservoir in the rear (for rear brakes) and a smaller one in the front (for front brakes)

The car is disc front and drum rear and I have always been under the impression that that would take a reservoir that had two different size reservoirs...???

Upon a test drive I found that the rears were awesome and the fronts don't seem to be working at all even when doing a "panic stop"...

Any help would be greatly appreciated....

Here is a pic of the new one...

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Sounds kind of obvious but you DID buy for front disc/rear drum correct?? Because I NOW have front disc/rear drum but HAD drum/drum which the master cylinder previously WAS just as you described. Perhaps the parts shop gave you the wrong one? (Cause they NEVER do that, bahaha) I would double check. Has your car ALWAYS been disc/drum or did you swap?? And that could def cause your symptoms, the MC for my 72 disc/drum - drum/drum are 2 different part numbers. Hope that helps a smidgen :)


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Discussion Starter #4
Sounds kind of obvious but you DID buy for front disc/rear drum correct?? Because I NOW have front disc/rear drum but HAD drum/drum which the master cylinder previously WAS just as you described. Perhaps the parts shop gave you the wrong one? (Cause they NEVER do that, bahaha) I would double check. Has your car ALWAYS been disc/drum or did you swap?? And that could def cause your symptoms, the MC for my 72 disc/drum - drum/drum are 2 different part numbers. Hope that helps a smidgen :)
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When I opened the box and saw it I immediately call them and asked and when they double checked they said that it is for a disc/drum...
Now, that being said...my old MC had the large res in the back for the rear brakes and the small one was for the fronts...
Who the heck knows if it has always been etc as it is 40 yrs old...
 

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Discussion Starter #5
I believe you have a drum to drum master, the reason for the larger front resivior is to allow more fluid to push the pistons of the front caliper. I have that exact master on my 4 wheel drum car.

Here's what you should have.
http://www.ss396.com/mm5/merchant.mvc?Screen=PROD&Store_Code=Nova&Product_Code=FMP-070&Category_Code=MASTERCYLINDER
Thanx Taz but again...on my old one, the LARGE res was on the rear and ran the rear DRUMS and the SMALL res was on the front and ran the front DISC brakes...
Was that wrong...???
BTW...the brakes on this car have never been right :rolleyes:
 

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Thanx Taz but again...on my old one, the LARGE res was on the rear and ran the rear DRUMS and the SMALL res was on the front and ran the front DISC brakes...
Was that wrong...???
BTW...the brakes on this car have never been right :rolleyes:
That's odd, do you have a pic of it to post? Have you checked to be certain the front lines were not connected at the rear of the master with the larger resivior?

The larger resivior is needed for the larger piston displacement of the caliper, where the wheel cylinders are smaller and the rears have adjusters, so extra fluid isn't need to compensate as they wear.
 

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Just throwing this out there (anyone with a better idea please feel free to chime in) but since you say the brakes have never been right, it sounds to me like the proportioning valve might be at least part of the problem.
 

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Discussion Starter #8 (Edited)
That's odd, do you have a pic of it to post? Have you checked to be certain the front lines were not connected at the rear of the master with the larger resivior?

The larger resivior is needed for the larger piston displacement of the caliper, where the wheel cylinders are smaller and the rears have adjusters, so extra fluid isn't need to compensate as they wear.
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This is the only pic I have...It's hard to tell but the large res is in the rear and here you can see that the rear line does go to the rear and the front line splits leaving the porp valve and goes to the left front and the right front...
Of course this is NOT the way it left the factory although all of the lines look unmolested as tho they are in the original location...
Could the original res have been large in the front and small in the rear...?
You can also see the lines better in the original pic at the top because it shows it with the prop valve cleaned up and the new line going to the rear...
Thanx for your help! :)
 

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Discussion Starter #9
Just throwing this out there (anyone with a better idea please feel free to chime in) but since you say the brakes have never been right, it sounds to me like the proportioning valve might be at least part of the problem.
I am pretty sure the valve IS working....
Tell me if I am wrong but if the valve wasn't working OR had slid to one side or the other, I don;t think that all four would bleed...?????

Also...for some reason I recall that as a young guy growing up most master cylinders were "front goes to the rear and rear goes to the front" as far as the reservoirs were concerned...??? This one is front/front and rear/rear....

Also...when I say "they have never been right" keep in mind that the "never" means about one year that I have owned it....
Thanx!
 

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Discussion Starter #10
OK....looking at pics on parts store websites it does appear that not only do I have the wrong mc but I also had the wrong one before (the one with the large res in the rear)
Here is a pic from Autozone's site showing the large in the front...
SO.....I guess that solves the problem...
Thank you so much again for all of your help :)

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