Brake master cylinder bore size versus output pressure ?
#2144036
08/30/16 06:42 PM
08/30/16 06:42 PM
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Joined: Aug 2003
Posts: 43,252 Bend,OR USA
Cab_Burge
OP
I Win
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OP
I Win
Joined: Aug 2003
Posts: 43,252
Bend,OR USA
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I have a question for those more knowledgeable about hydraulic pressure and selecting the best bore size on brake master cylinder sizes. I have heard the smaller the bore size the more line pressure you will have to the brake cylinders. Is this correct? The reason I'm asking is that I'm going to replace the single master cylinder with a later model Mopar aluminum with dual reservior on my 1966 Dodge Coronet with a SSBC disc brake conversion kit with 11 inch rotors and 4 piston iron calipers up front and stock 10.5x2.5 drum brakes in the back. I'll put in a proporsioning valve and remove the residual valve in the M.C. for the disc brakes, if it has one. I don't know the bore size of the front caliper pistons or the pistons in the back, sorry What size M.C. bore size would be best in your opinion,1 1/8, 1.0, 7/8 inch I.D. or what size
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Brake master cylinder bore size versus output pressure ?
[Re: Cab_Burge]
#2144046
08/30/16 06:54 PM
08/30/16 06:54 PM
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Joined: Jul 2013
Posts: 1,272 Northern Calyfornua
Sxrxrnr
pro stock
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pro stock
Joined: Jul 2013
Posts: 1,272
Northern Calyfornua
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Replaced front drums on my Ebody, non power brake car. 1 1/8 stock mc
After market disc brake kit from well known 3rd party supplier. Wilwood Dynalites
Horrible front brake performance. Following some advice, installed a set of pads that gave adequate performance, but were filthy dirty.. Filthy after 10 or 20 miles. Supplied by Hawk.
After extensive research, replaced mc with a 15/16 inch mc picked up from Amazon for 50.00 and installed with ceramic pads, also from Amazon. Smaller mc bore = higher brake pad pressure.
Front braking infinitely better,,,can now lock them,,,and do not have to clean wheels after each 10 miles of driving.
Then had to deal with rears, as car was once a SS/E drag race car, rear self adjusters had been removed and Bubba had replaced with pair on both wheels of some star wheel adjusters from God knows what model car,,,but both of them were marked as right side.
All well now
Your results may vary.
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Re: Brake master cylinder bore size versus output pressure ?
[Re: lewtot184]
#2144084
08/30/16 07:42 PM
08/30/16 07:42 PM
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Joined: Jan 2003
Posts: 25,903 Rio Linda, CA
John_Kunkel
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 25,903
Rio Linda, CA
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I have a disc/drum combo with manual brakes. Went from a 1 1/32" MC to a 15/16" to get more pressure but just wound up with a lower/softer pedal and no noticeable braking improvement.....went back to the 1 1/32" and all is good.
The INTERNET, the MISinformation superhighway
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Re: Brake master cylinder bore size versus output pressure ?
[Re: Cab_Burge]
#2145738
09/01/16 10:21 PM
09/01/16 10:21 PM
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Joined: Feb 2005
Posts: 4,318 Prospect, PA
BSB67
master
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master
Joined: Feb 2005
Posts: 4,318
Prospect, PA
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The relationship in pressure change is proportional to the difference in piston surface area. It is no more or less complicated that this. You are simply converting pounds of force to pressure (pounds per square inch). Because area changes exponentially with diameter change, it does not take a lots to affect the pressure change.
For a given pedal force, the 15/16" bore will give a 30% increase in line pressure over a 1 1/8" bore.
Last edited by BSB67; 09/01/16 10:22 PM.
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Re: Brake master cylinder bore size versus output pressure ?
[Re: lilred]
#2147198
09/04/16 10:34 AM
09/04/16 10:34 AM
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Joined: Sep 2003
Posts: 19,534 north of coder
moparx
"Butt Crack Bob"
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"Butt Crack Bob"
Joined: Sep 2003
Posts: 19,534
north of coder
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the wagner pn for the 4 bolt, 15/16" manual disc brake master is : F80266. check the piston bore for the rubber retainer groove, as it seems lately, this part# is used for both manual and power brake applications and may, or may not not have the retainer groove in the piston. in power applications, the groove is not needed. if you use a non grooved master in a manual application, you MUST make sure there is a positive, non moving, stop installed to prevent the pedal push rod from falling out of the master cylinder piston bore. as can be imagined, if the pedal push rod falls out of the piston bore, you may experience a very bad day. i don't know if the bendix or raybestos brand masters are set up the same way, but please check to make sure you know what you have and make any necessary adjustments as needed.
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