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Need help determining what Master cylinder bore size to go with.

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Black_57

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Discussion starter · #1 ·
Ok, I'm looking at getting the CPP MCPV-1 for my 57.
The car has the large GM front disc brake calipers, and I just converted the rear disc brakes so that they are using the 79 Eldorado rear disc brake calipers. (Had stock drums before)
The car has a dual 7" or 8" brake booster.

In the future I will probably go to dual piston front brake calipers (probably PBR C15's) BUT want to avoid doing that now as this build has already snowballed.

But with the current configuration, will the 1-1/8" bore size work properly?
 
#3 ·
Rick_L said:
1-1/8" is good with those calipers and an 8" dual booster. You might consider 1" with the dual 7" booster. Recommend the 8".
Click to expand...

Rick is correct except for the 1" with a 7" booster. The master should be 1 1/8" regardless of the booster. Less assist will not change the master size affects, even with very little assist the 1" will still go close to the floorboard unless you have zero assist which is no booster
 
#4 ·
Disagree. The 1" master cylinder will give you 26% more line pressure for a given force on the pedal. The travel will be the same as stock manual brakes, since they use a 1" master cylinder.

Now is that the most desirable? Maybe not compared to the 8" booster and 1-1/8" master cylinder.
 
#6 ·
I just posed a similar question to Wilwood yesterday we are removing the offset CPP bracket & dual 8" 2 year old booster that just took a sh-- & my buddy wants to go to a manual brake set up for a cleaner look so I called Wilwood to ask which master cylinder they would recommend using D52 calipers & drum in the rear.I figured a 1" but the tech guy said definitely to use 11/8 with those calipers & no booster.
 
#8 ·
56ls408 said:
I just posed a similar question to Wilwood yesterday we are removing the offset CPP bracket & dual 8" 2 year old booster that just took a sh-- & my buddy wants to go to a manual brake set up for a cleaner look so I called Wilwood to ask which master cylinder they would recommend using D52 calipers & drum in the rear.I figured a 1" but the tech guy said definitely to use 11/8 with those calipers & no booster.
Click to expand...

I've heard similar stupidity from them. Tech guy today, pizza delivery yesterday
 
#9 ·
56ls408 said:
I just posed a similar question to Wilwood yesterday we are removing the offset CPP bracket & dual 8" 2 year old booster that just took a sh-- & my buddy wants to go to a manual brake set up for a cleaner look so I called Wilwood to ask which master cylinder they would recommend using D52 calipers & drum in the rear.I figured a 1" but the tech guy said definitely to use 11/8 with those calipers & no booster.
Click to expand...

I have to add that wilwood's D52 is not the same size as a GM D52. Their total piston area is less and could technically get by with a slightly smaller bore
 
#10 ·
We are using the GM style of D52 calipers & I told the Wilwood tech guy that when speaking with him.yes I know they're version of the D52 is different I never seen much reason to use them other than looks.They're larger calipers are a different matter on my own 56 I'm using factory C6 calipers & rotors.
 
Discussion starter · #12 ·
56ls408 said:
CPP bracket & dual 8" 2 year old booster that just took a sh-- & my buddy wants to go to a manual brake set up for a cleaner look so I called Wilwood to ask which master cylinder they would recommend using D52 calipers & drum in the rear.I figured a 1" but the tech guy said definitely to use 11/8 with those
Click to expand...
That's seems contrary to what I've seen on other sites... I was under the impression that If you were running a 4 disc (maybe even a disc/drum setup) with a dual 8" booster or especially Hydroboost, you should run a 1-1/8" MC..
To my thought process, manual brakes vs hydroboost would be on opposite sides of what would be needed.
 
#13 ·
You're right on the 1-1/8" bore if you have decent assist. There's another active thread that discusses using 15/16" or even 7/8" with manual Wilwood stuff. Size the master cylinder to the front calipers and boost. Rear does not matter to m/c selection, disc or drum. You'll probably be killing off some rear brake with a proportioning valve.
 
#15 ·
56ls408 said:
I just posed a similar question to Wilwood yesterday we are removing the offset CPP bracket & dual 8" 2 year old booster that just took a sh-- & my buddy wants to go to a manual brake set up for a cleaner look so I called Wilwood to ask which master cylinder they would recommend using D52 calipers & drum in the rear.I figured a 1" but the tech guy said definitely to use 11/8 with those calipers & no booster.
Click to expand...
I can tell you this, you will not be at all happy with a manual setup with a 1-1/8 master unless you have king kong legs. I have the exact setup d52 caliper and drum rear and the sweet spot for braking effectiveness vs pedal effort was a 15/16" master cylinder.
 
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#17 ·
I did a 1.063 master and it was almost not drive-able as it was to dam hard to push. I called willwood and they said 7/8-15/16 I went 15/16 and it was decent. about 1/2 travel and very controllable
 
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#18 ·
I'm running C4 manual disc brakes F/R with a Wilwood 7:1 pedal. Started with dual 7/8" cylinders and pedal pressure was a bit too much. Now I am running 3/4 cylinders which is the smallest they have, and brake pedal pressure is much better. Pedal travel is about halfway down at 1200 psi, and it stops great.
 

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#19 ·
56ls408 said:
Am I right in assuming both Rick & Slim agree (rare) that a 1" master with manual disc & drum setup is the preferred master cylinder over a 1.125" master?
Click to expand...
I actually have a 15/16" master with the big calipers and rear drum. Plenty of pedal and not a lot of foot pressure needed on the pedal. No want what so ever for power brakes, even if it were free. They work great as is. Oh, and I do have (I can't think of the brand name now) some type of "hot rod" brake pads that grab better than the modern :poop: at the auto parts store that are basically made for power brakes.
 
#20 ·
55 Rescue Dog said:
I'm running C4 manual disc brakes F/R with a Wilwood 7:1 pedal. Started with dual 7/8" cylinders and pedal pressure was a bit too much. Now I am running 3/4 cylinders which is the smallest they have, and brake pedal pressure is much better. Pedal travel is about halfway down at 1200 psi, and it stops great.
Click to expand...
That's the only real way to still have brakes if the front or the rear go out. The dual master cylinder and combination valves are a crap shoot, if any really work great at all. I know mine never did. Maybe 10% of original braking power at the most. Not full front or full rear if the other goes out.
 
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