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Discussion Starter #1
I’ve been searching on here and I see that if you change to disc brakes on the front that you do and you do not need a brake booster.

My question is: which one is it yes or no Needing a brake booster?

i have the disc conversion in a box ready to go when I get to that point but I am hoping the answer is no because I’m planning on using the new McLeod hydraulic clutch for the Muncie. It’s ok if I have to I’m not worried about it I was just about to hit order on the McLeod.
1965 Chevy II
 

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I’ve been searching on here and I see that if you change to disc brakes on the front that you do and you do not need a brake booster.

My question is: which one is it yes or no Needing a brake booster?

i have the disc conversion in a box ready to go when I get to that point but I am hoping the answer is no because I’m planning on using the new McLeod hydraulic clutch for the Muncie. It’s ok if I have to I’m not worried about it I was just about to hit order on the McLeod.
1965 Chevy II

No is my answer. You will need a different master cylinder with a smaller bore. I use a 7/8" bore Wilwood on my car.
 

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I had power brakes (7" dual diaphragm booster) on my car and recently swapped it over to manual brakes. My motor did not make enough vacuum to have really good power brakes. I run autocross and Wilwood recommended a 15/16" bore master cylinder. I am pretty happy with the manual brakes. There is not much room under the hood of these cars to begin with. Eliminating the power brake booster made it easier to access my spark plugs, wires, etc. and eliminated some clutter from under the hood.
 

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Most of us here will probably go to a boosted brake system as this is standard fare on modern vehicles and we are accustomed to these type of systems.. What you have to keep in mind is that if you are considering using a vacuum booster and you haven’t got the specs for the cam shaft in your 331 engine. If you have a big cam you probably won’t be able to develop enough vacuum pressure in the engine to operate the vacuum booster..
 

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Discussion Starter #6
I had an Isky racing cam in it but I would like to stay in the 108-110 lobe separation nothing too huge. I agree with likening the feel of the new softie brakes but I don’t mind working up the calf muscles and I can use the Muncie to help
 

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Discussion Starter #7
I see 7/8” and 15/16” is there really that much difference between the two? I know I need a double outlet master and wilwood is the way I’d like to go as my clutch pedal is wilwood and I love it
 

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I see 7/8” and 15/16” is there really that much difference between the two? I know I need a double outlet master and wilwood is the way I’d like to go as my clutch pedal is wilwood and I love it
Wilwood told me that the 7/8" would give me a softer pedal feel, but the pedal would travel further before it started braking. I run autocross so they recommended the 15/16" bore which gives me a little firmer pedal but less travel. I think you would be happy with either.

If you do the math, the 7/8" piston has only 87% the area of a 15/16" piston. This means that the 7/8" pedal should have about a 13% softer feel to achieve that same braking power than the 15/16". So, it is a matter of preference. Do you prefer a firmer pedal feel or a softer? Do you do any spirited driving or do you have a Sunday cruizer?
 

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Measure the didtance from the brake pedal pivot and the point where the rod attaches and measure the distance from the pivot and the center of the pedal pad. Measure the diameter of your caliper pistons and how many you have. Call Wilwood tech and they will fo the math.
In other words, pedal ratio and piston dia are the determining factors. Let the experts give you the size.
 

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Discussion Starter #11
That’s a good point till I get Stan who has only started for a week but I don’t know that. That is why I was preparing with info before I called up is all. Thank you Alf
 

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It is my understanding the main factor on determining bore size for master cylinder is brake caliper size and number. The standard GM single caliper would need 1" bore while the newer 6 caliper disc would use smaller bore. I also agree with the statements that smaller bore equates to softer pedal and more pedal travel. So, advice from Alf is spot on. Determine what brake set up you have or what you want to go to, call Willwood and they can tell you the best master to use.
 

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I did a front disc conversion on my 65 with the stock non power master. No problems whatsoever. Upgraded to rear discs and a 1" Wilwood non power, no problems. Slightly stiffer pedal when you romp on it but its very linear and controllable. Plus the engine bay looks so much cleaner and everything is easily accessible without a booster.
 

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Discussion Starter #15
That is what I like to hear especially if I go with the McLeod hydraulic system, makes it look cleaner and easier to access. The one guy on here has a very detailed record of what he did to get his together and it was a great help
 

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My car had been converted from 4 wheel drums to GM front discs when I got it. Brakes are not strong, so I have been considering a power booster, but, I'm not sure that would help; it could be my master cyl is not a good match for the front discs (assumed to be for manual drums?) or the prop valve going to the rears could be maladjusted. See attached pic. The prop valve is located right under the drivers door, and I have no idea what direction to turn the knob to adjust the flow to the rears. Help!
 

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Hard to tell from the picture but the master cylinder looks like original. If it is, that could be your problem. Not set up for disc front drum rear. Sorry but I'm not much help on adjusting prop valve or if can be. Maybe someone else will chime in. Car is 72, right?
 

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The master cylinder is not original, it's a C2/C3 Corvette style. Most are 1", but some can be 1-1/8".

What is your pedal ratio? Stock manual brakes should have the clevis in the upper hole on the brake pedal and a 6:1 ratio. Stock power brakes would have the clevis in the lower hole and a 4:1 ratio. You want the 6:1 ratio.

What calipers do you have? If they are GM single piston, a 1" m/c will work, but you may prefer the Wilwood 15/16". If you have aftermarket or late Corvette/Camaro calipers, then you want something smaller, probably 7/8" or 15/16".
 

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My car had been converted from 4 wheel drums to GM front discs when I got it. Brakes are not strong, so I have been considering a power booster, but, I'm not sure that would help; it could be my master cyl is not a good match for the front discs (assumed to be for manual drums?) or the prop valve going to the rears could be maladjusted. See attached pic. The prop valve is located right under the drivers door, and I have no idea what direction to turn the knob to adjust the flow to the rears. Help!
If you can't lock up the tires with the current manual brakes, adding a power booster won't help that one bit.
All a power booster does is reduce the amount of leg effort needed to push the pedal down, it does not magically decrease stopping distance. It was developed as a convenience feature, to attract female buyers and the older generations....grandmas and soccer moms.

if you've got the larger 1-1/8" or 1-1/6"" bore master meant for use with a brake booster, pedal will be harder and actual pressure at the calipers and wheel cylinders will be lower than if it had the correct 15/16" or even 7/8" bore master cylinder.
Knob on adjustable prop valve is just like a bolt.....clockwise is tighter, reduces pressure to the rear...counterclockwise is looser, opens the line to the rear more.
 

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The master cylinder is not original, it's a C2/C3 Corvette style. Most are 1", but some can be 1-1/8".

What is your pedal ratio? Stock manual brakes should have the clevis in the upper hole on the brake pedal and a 6:1 ratio. Stock power brakes would have the clevis in the lower hole and a 4:1 ratio. You want the 6:1 ratio.

What calipers do you have? If they are GM single piston, a 1" m/c will work, but you may prefer the Wilwood 15/16". If you have aftermarket or late Corvette/Camaro calipers, then you want something smaller, probably 7/8" or 15/16".
Thanks for all that info. I DONT know whats on it exactly, but evidently you could tell from looking that its a Vette MC, probably a 1". I s/b able to look at the pedal and figure out if its pivoting at the top or bottom holel- and I need to use the upper hole! Figure the caliper are just stock single GM items- look newer, so probably Chinese. So could I add a booster and still use this MC? I have plenty of vacuum.
406183
 
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