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master cylinder


John S

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Does someone have a picture of the correct master cylinder for a 1970 monte w/ PB. I have seen a couple of types one with a single bale and one with two. Which one is correct? Or are both types correct?

John S

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John,

It is my understanding (and I believe I also verified this with both the GM Assembly and Service manuals several years ago) that GM assembly plants used the Delco Moraine and the Bendix master cylinders interchangeably when they built 1970 Montes (not sure about '71s & '72s).  Their bolt patterns and line connection ports are positioned exactly the same, however, they look different, have different shaped covers and require different length actuator rods to function correctly with a common vacuum booster.

I have had and used both brands on my '70s and they are functionally equivalent.  Both brands had single bails as shown in photos below.  I have seen dual bails on the Delco Moraine unit but not on the Bendix.  I don't know if the dual bail units are OEM replacements, original factory or perhaps for some other GM vehicle.

Several years ago, I replaced the leaking Delco master cylinder on my '70 SS with a re-manufactured unit that turned out to be a Bendix.  It bolted right up and came with the correct length actuator rod.  I much prefer the squarish look of the Delco unit so I kept my original and have planned to rebuild it myself (someday).

 

Delco Moraine (original factory unit)

P9220993.JPG

 

Bendix (Re-manufactured Unit)

P9083665.JPG

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Thanks I have the square one. Good to know if I replace with the Bendix type I will need the correct  actuator rod also. Having a little brake issue now. Pedal feels "different", feels hard, how's that for specific. When I rebuilt the calipers and took it on first test ride I had maybe 20% front brakes. I believe maybe the piston, or ball in the proportioning valve may have shifted. I then learned that the brake light did not work at the proportioning valve switch. By loosening some brake lines and jamming the pedal hard I believe I reset it as the front end dives and feels better but when I hit the brakes hard  they will not lock up, did the Fantomworks 3,2,1 hit the brakes hard test. I pressure bled brakes and I did use a wedge to push the "button" on the metering valve in when bleeding both manually and with the pressure bleeder. The last time I manually bled them I did not use the wedge for the metering valve, and they did bleed fine except it was slow on the first pump. I am leaning toward the booster but that seems to pass the tests that I read about to test it. Check valve is OK vacuum line to booster is not collapsed. I am thinking booster, master cyl., or proportioning valve. Or maybe metering valve. Eventually I will figure it out I usually do but if anybody has any ideas I'm listening.

John S

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I have had issues like you are describing. Check or change the rubber hoses to the calipers and the one to the rear end. They swell up inside or collapse, however you want to call it . Very common.

A bad booster usually gives you a rock hard pedal at all times. 

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I will check them again but I replaced them three years ago. They may very well be bad, with the way things are made today they don't last like they used to. Usually I try to figure out the only thing that changed, and that is the banjo bolts. The old ones had the 5/8 hex head and the new ones I put on are the ones with a 7/16 hex head flange bolt. Both banjo bolts are 7/16 - 20.

John S

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1 hour ago, Paul Bell said:

Which of the factory original master cylinders had bleeders above the line ports?

MC.jpg

Paul, I don't believe any of the original factory master cylinders had those bleeding ports.   That was a later invention and can be had on the Delco Moraine replacement units for sure (as shown in your photo).  That is a great new feature, IMO.

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The original master had the bleeders as Paul stated. I have seen and had many. The original for my 70 SS, which I still have, has them. Maybe it was at only certain plants, the Monte's I have had them on we're mostly Baltimore cars and my SS was built in the Flint plant. 

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My 71 has the bleeders and looks like Paul Bell's picture above.

I STRONGLY recommend nobody EVER turns in an original for the core charge in case the replacement turns out to be wrong, you will wish you still had it!

I rebuilt mine, years ago, very easy to do.

Bruce 

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Sorry guys, I didn't mean to mislead anyone.  Both of my '70s came to me with Delco Moraine master cylinders WITHOUT the bleeders. One was built in Baltimore the other in Van Nuys.  Also, the re-manufactured Bendix replacement I bought for my '70 SS did not have them.   I would be most happy to have a master cylinder with the cast-in bleeder ports and valves, regardless of originality or brand.

It is often difficult to tell what is original and what has been replaced on our cars when we are not the original owner with good records or recollections.  Also, as someone else pointed out, assembly plants were sometimes known to use functionally equivalent parts that were not identical to others.  This makes it difficult to claim absolute "originality" on many features of our first gens, IMO. 

 

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2 hours ago, Paul Bell said:

HUH? Got a pic?

 I don't have a picture  mine does not have one. As Dennis stated earlier these cars have been through many owners and you do not know what was taken off or what was put on whether it was original or not.   John S

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