Disc brake master cylinder

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dartswinger71318

dartswinger71318

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I'm upgrading the brakes on my 69 Dart, from drum brakes to Kelsey Hayes 4 piston disc. Any suggestions on a master cylinder and propositioning valve I've seen that the rear sump needs to be larger than the front, for disc setup but I'm not 100% sure.
Any help is appreciated
 
dartswinger71318 said:
I'm upgrading the brakes on my 69 Dart, from drum brakes to Kelsey Hayes 4 piston disc. Any suggestions on a master cylinder and propositioning valve I've seen that the rear sump needs to be larger than the front, for disc setup but I'm not 100% sure.
Any help is appreciated
Click to expand...
they way i did this is i bought a jegs adjustable prop valve like 49.99 i think. on the original prop valve i disconnected the rear line plugged it up. connected the new prop valve to the rear line and ran a new line to the master cylinder. The master cylinder for disk is not the same one for the drums. heres what i used CARDONE 131493M
 
Disc brake M/C's are different from drum brakes, the most obvious difference is a larger reservoir for the discs due to their need for greater volume. A proportioning valve is needed to equalize pressures for disc/drum combo's. If you add power to the brakes, then the M/C is again a little different.
 
Murray said:
Disc brake M/C's are different from drum brakes, the most obvious difference is a larger reservoir for the discs due to their need for greater volume. A proportioning valve is needed to equalize pressures for disc/drum combo's. If you add power to the brakes, then the M/C is again a little different.
Click to expand...
No I'm staying with the manual system, like the clean look in the engine compartment.
 
The Cardone/Bendix/Dorman replacement unit would look like this. Note that the two ports are different sizes. You may need a brass adapter if you aren't replacing the hard lines.
Screen Shot 2020-07-02 at 2.28.47 PM.png
 
This is the one I used with the Kelsey Hayes 4 piston set up. Front disc rear drum

IMG_1120.PNG
 
dartswinger71318 said:
Im curious Is the rear sump larger than the front, I was under the impression it needs to be to supply the additional pressure for the disc brakes.
Click to expand...
There the are the same on the 4piston, on the later 73 disc brakes they had the style,a bigger and smaller reservior combo make sure to run the front disc brake line to the first reservoir.
 
Go to NAPA and get a reman m.c. from a 73-76 dart/valiant with disc brakes , no power get the valve also . The m.c. is $38.00 plus core . rockauto.com has 'em too . FYI, the brake line is 3/16ths, different fittings are needed , need a flaring tool too.
 
That picture is a DRUM brake master cylinder! That master cylinder is NOT a disc brake master cylinder! I've seen quite a few times in the past where people have gotten the wrong master from the parts store, when they go back and have the parts guy dig a little deeper they usually find the right one. There aren't to many disc brake master cylinders available for the 67-72 A bodies. The ones for 73-76 are readily available in both manual and power.
 
dartswinger71318 said:
Im curious Is the rear sump larger than the front, I was under the impression it needs to be to supply the additional pressure for the disc brakes.
Click to expand...
The larger reservoir for disc brakes is about the larger amount of fluid calipers consume especially as the pads wear and piston is out farther. wheel cylinders for drum brakes contain very little fluid. If brakes stay adjusted properly the amount of fluid in them doesn't change.
 
Slantsix64 said:
There the are the same on the 4piston, on the later 73 disc brakes they had the style,a bigger and smaller reservior combo make sure to run the front disc brake line to the first reservoir.
Click to expand...
This is incorrect.
Slantsix64 said:
nope look up the part number the picture is cut off cause of the screen shot. Says front disc rear manual drums
Click to expand...
Yes and no.
What has happened is the big aftermarket companies like A1 Cardone figured out they could resell drum brake master cylinders as disk/drum masters by removing the residual valve on the rear port (to front brakes). It works good enough for most of the time. Now what happens as the pads wear is the piston starting position moves out. That's what Redfish just explained. The extra fluid in the resevouir ensures there is always enough to keep the front lines and calipers filled. It also helps having cooler fluid available for multilple high speed stops.

But most of the time the smaller resevoir was enough. Cardone and the others don't really care that occassionally it may not be. If there is an accident and some expert points out this was a contributing factor then lawyers will get involved. Their lawyers will either settle or argue that you or the mechanic should have checked and topped off the master cylinder more frequently - whichever will cost them less.

So how do you know what I just wrote is correct or just BS?
One way is to go the factory information. The shop manuals show this and sometimes explain it. Even better in this case are the Chrysler Master Tech booklets about brakes and brake hydraulics. Thanks to the internet and some dedicated hobbyists, this is all available on the internet, at least for now.
Master Technician Service Conference - Chrysler's Training for Mechanics
Some of the newer ones not available at the club are available on a commercial website mymopar.com

For an overview of the different masters there is a pdf reprint of the "Pumping points" article available at moparts.com
 
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