Heads up to those that install a 2 bolt aluminum master cylinder.

-
Typical mc the rear piston does not come in physical contact with the front piston, it builds pressure between the two pistons, and hydrolic pressure applies the front piston. If you have ever noticed one resivour go down in level and the other rise, that indicates a bad part in the MC.

BTW there is an aluminum 4 bolt stock looking MC available.

Also 1 1/8 is huge as compared to the 1" stock to 15/16 pistons.

That alone could account for the increased foot pressure needed to stop.
 
The 1 1/8" bore is large, I agree.
Dr Diff suggested this for the use with a hydroboost setup that I was first working with. I couldn't get the HB working so I tried a 15/16" manual setup. That didn't feel right so I'm back with the power booster. I figured that if the 1 1/8" unit was right for the hydroboost, it should work with the vacuum booster. If it results in a weird pedal feel, I still have the 15/16" unit to try.
 
Cass just responded.
The ports are correct and they are sized differently to ensure proper orientation. I thought they might have been reversed but they are not.
He stated that the Mancini unit could be used for GM and Ford applications as well as Drag race cars where the bias could be to the rear due to large rear tires.
I'm just frustrated and looking for answers. Sometimes those answers are hard to find.
 
Oldmanmopar said:
Go to a parts store and buy a master cyl for a 1979 Dodge Ram manual brakes. I could put someone through the windshield at 100mph. If installing it in an a-body with and adapter use a E-body or B-body brake push rod . This gives the extra length to make up for the adapter.

View attachment 1716014192
Click to expand...

I have Dr. Diff 15/16 master and the adapter. I've always thought, I needed a different rod, but Cass says no, sock rod works fine??
 
I'm running a wilwood MC with the adjustable prop valve. It defiantly has the front port of the MC tied to the front brakes and the rear port tied to the adjustable prop valve going to the rear brakes. After checking the instruction sheet this is how it shows it should be. But my brakes have never been that great. I'm thinking I might purchase a Mopar 15/16s MC and reverse the lines and give it a try.
 
plumkrazee70 said:
I have Dr. Diff 15/16 master and the adapter. I've always thought, I needed a different rod, but Cass says no, sock rod works fine??
Click to expand...
certian master cyl do not need the new push rod. they are drilled shallower then the original master cyl. the adapter plate makes up for the difference so you can use the stock push rod.
 
i had trouble finding an alum master cyl that wasn't beat to hell at the tim that i needed it. i ended up calling RMS and just getting a wilwood one that looks just like the mopar one. been working great for over a decade.
 
Disk always has a larger reservoir as the caliper pistons displace more fluid that the drum brakes.
I don't know why the MC has anything to do with proportioning. Usually the prop valve directly applies pressure to one side and has a tight spring that moves with pressure to delay uncovering the other port? Not sure what gets the first application. What you wanna lock up first?
 
Dana67Dart said:
This is the one I know about.

I have not used it

1962-74 Mopar Bendix Style ALUMINUM Master Cylinder
Click to expand...
This is an excellent option and cheaper than the plastic reservoir models.





​
​
1672080494.png


1664330609.jpg


1664364015.jpg


1664364020.jpg


1664364025.jpg


1664330618.jpg


1664348289.jpg















Store/MASTER CYLINDERS, AND PUSHRODS/MASTER CYLINDERS, BOLTS AND HARDWARE

1962-74 Mopar Bendix Style ALUMINUM Master Cylinder, 1-1/32 bore for disc/drum and disc/disc applications​


$81.75
 
DionR said:
I have one on my car from Ehrenburg and am happy with it.

I remember him saying that just any aluminum MC will NOT do, and to NEVER use a FWD one. Maybe this is why he warned against it? Not saying it is, just wondering if there is a correlation.
Click to expand...
Thats because most FWD cars have a X style brake system RF to LR and LF to RR.
 
mmm im wandering if thats why i dont have a good pedal and have to pump the pedal for a good stiff feel i front and rear disks

MASTERCYLINDER BRACKET 004.JPG
 
Today I lined up all the master cylinders that I have gathered....

img_1207-jpg.jpg


img_1208-jpg.jpg


Out of view is an aluminum 15/16" unit and the aluminum 1 1/8" MC on my car.

Three are cast iron 4 bolt units. One at 1" and two of them 15/16".....They all had 9/16" front ports, 1/2" rear ports and when bench bled, pushed fluid equally in time front and rear.

Two of the aluminum units were 1.03" and had 9/16" front, 1/2" rear ports and pushed fluid equally.
One aluminum one was 15/16" and had weird 3/8" ports. The front reservoir was longer but the whole reservoir was sloped. See picture below:

d-diff-mc-1-jpg.jpg


It pushed fluid to the front first.

The final two MCs are the ones I've been working with lately. Both 15/16" and 1 1/8" units have identical ports and push fluid to the front reservoir first.
 
Oldmanmopar said:
Go to a parts store and buy a master cyl for a 1979 Dodge Ram manual brakes. I could put someone through the windshield at 100mph. If installing it in an a-body with and adapter use a E-body or B-body brake push rod . This gives the extra length to make up for the adapter.

View attachment 1716014192
Click to expand...
Pretty sure MP still offers an adjustable brake pushrod.
Kern Dog said:
This is the part number for that unit. It shows the different port thread sizes. The rear port on mine does have the smaller threads so it does have the traditional arrangement.

RAYBESTOS MC39178 Specifications
Number of Ports2
Primary Port Thread A1/2"-20
Secondary Port Thread A9/16"-20

I'm still curious as to why I'm getting fluid to the rear brakes first.
Click to expand...
Best guess: there's something wrong with your MC.
 
Kern Dog said:
This is an excellent option and cheaper than the plastic reservoir models.





​
​
​
View attachment 1716014277

View attachment 1716014278

View attachment 1716014279

View attachment 1716014280

View attachment 1716014281

View attachment 1716014282

View attachment 1716014283














Store/MASTER CYLINDERS, AND PUSHRODS/MASTER CYLINDERS, BOLTS AND HARDWARE

1962-74 Mopar Bendix Style ALUMINUM Master Cylinder, 1-1/32 bore for disc/drum and disc/disc applications​


$81.75
Click to expand...
It's twice the cost or more of a stock plastic-cap MC. They're <$40.
 
The aluminum bodied master cylinders I mentioned look similar to the cast iron ones. My point was that they allow the appearance of a stock one with less than half the weight.
 
Thought I'd add my experience since I've got the same Dr. Diff setup as the OP - 13" front / 11.7" rear with 15/16" MC. When I first bench bled the MC there was absolutely no fluid movement out of the rear port until nearly half the piston stroke - the front port had fluid movement immediately when the piston was moved. I contacted Dr. Diff and he sent me another new MC. When I bench bled that one I thought I saw some improvement, but I believe the results were largely similar. Since I admittedly had no previous experience in this area I assumed the fault was mine and went ahead and installed it. This was last summer, and the car still has a ways to go before it will be running. If the ports are truly reversed that would explain a lot - I will be following this thread to see if more information on this comes to light.

1670191112763.png
 
You must log in or register to reply here.
-

Back
Top