Power to Manual Brakes - Master Cylinder Bore Size
#2741278
02/09/20 04:41 PM
02/09/20 04:41 PM
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Joined: Jan 2005
Posts: 4,366 Michigan
MarkZ
OP
Worthy
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OP
Worthy
Joined: Jan 2005
Posts: 4,366
Michigan
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I'm converting my car over to manual brakes this season. Setup is already four wheel disc, but getting different front calipers. - Rear calipers are single piston, 2.544 in² area with 11" rotors
- Front calipers are four piston Wilwoods, with 4.8 in² area with 11.75" rotors
- Brake pedal is the factory power pedal with a 4.5:1 ratio
What bore master cylinder should I be looking at? Should I also be looking for a pedal with a higher ratio? These cars were offered with manual brakes earlier in the model line. I've got to assume the pedal ratio was different. Thanks again Moparts!
1987 Fifth Avenue - 512/518/D60
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Re: Power to Manual Brakes - Master Cylinder Bore Size
[Re: MarkZ]
#2741357
02/09/20 08:11 PM
02/09/20 08:11 PM
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Joined: Jan 2003
Posts: 1,482 Lake Orion, MI
goldduster318
pro stock
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pro stock
Joined: Jan 2003
Posts: 1,482
Lake Orion, MI
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You're going to want more pedal ratio. I think original ones are typically 6-7:1 depending on the vehicle without measuring one.
'70 Duster 470hp 340/T56 Magnum/8 3/4 3.23 Sure-Grip
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Re: Power to Manual Brakes - Master Cylinder Bore Size
[Re: GoodysGotaCuda]
#2741536
02/10/20 12:23 PM
02/10/20 12:23 PM
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Joined: Sep 2003
Posts: 19,239 north of coder
moparx
"Butt Crack Bob"
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"Butt Crack Bob"
Joined: Sep 2003
Posts: 19,239
north of coder
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there is a calculator out there that when you enter the various items needed, will calculate the "effort in lbs" needed for leg input. i thought i had it saved, but i can't find it. it wasn't wilwood, but one of the others. it may have been a chassis builder. i just plain forget. [CRS strikes again ! ]
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Re: Power to Manual Brakes - Master Cylinder Bore Size
[Re: Jjs72D]
#2741875
02/11/20 10:44 AM
02/11/20 10:44 AM
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Joined: May 2019
Posts: 6,174 nowhere
Sniper
master
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master
Joined: May 2019
Posts: 6,174
nowhere
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I thought Feets made a spreadsheet awhile back. It's the top pinned thread in this forum. Link is in the last post in the first page of the thread.
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Re: Power to Manual Brakes - Master Cylinder Bore Size
[Re: moparx]
#2742170
02/12/20 08:22 AM
02/12/20 08:22 AM
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Joined: Nov 2004
Posts: 25,050 Texas
GoodysGotaCuda
5.7L Hemi, 6spd
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5.7L Hemi, 6spd
Joined: Nov 2004
Posts: 25,050
Texas
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there is a calculator out there that when you enter the various items needed, will calculate the "effort in lbs" needed for leg input. i thought i had it saved, but i can't find it. it wasn't wilwood, but one of the others. it may have been a chassis builder. i just plain forget. [CRS strikes again ! ] Correlating caliper pressure to stopping power is still an unknown. So if the calculator says 100lb leg force gives you 3,000psi at the caliper, then what? Vehicle inertia, rotor size and pad coefficient of friction are still out there..
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Re: Power to Manual Brakes - Master Cylinder Bore Size
[Re: Sniper]
#2742414
02/12/20 08:28 PM
02/12/20 08:28 PM
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Joined: Nov 2004
Posts: 25,050 Texas
GoodysGotaCuda
5.7L Hemi, 6spd
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5.7L Hemi, 6spd
Joined: Nov 2004
Posts: 25,050
Texas
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A good experiment only changes one thing at a time.
All else being the same, and it should be, you can use the math to decide what to do with your M/C bore size.
So start with what you have, put the numbers in get a value. test it as configured and if you want more stopping power, or less leg effort, you can substitute whatever values are available to get where you want to be.
If you like the leg effort but want more stopping power then you fool with pad friction coefficient or rotor sizing.
But you already know all this. Sure, if you are starting with a blank slate. Most of these situations come up with everything other than the master cylinder already being defined and purchased. Swapping pad coefficients can get you somewhere, but not all of it depending on your need. The intended use can very much dictate what pad will be needed and what pad will survive. Even with all of that, the subjective feeling of a extended pedal stroke to obtain the calculated pressure is also often ignored. The numbers can say that 100lb force gets you 3000psi at the caliper, but if it takes 4" of pedal stroke to get there, it is not comfortable to drive with on the street. It's too long and most people won't go for it. My point is, that you can try to pencil whip this into an answer, but you may very well find that you don't like what you thought you would like once it's all installed and running. Buy what you think is right and be ready to adjust up/down a size, if needed.
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Re: Power to Manual Brakes - Master Cylinder Bore Size
[Re: AndyF]
#2742876
02/14/20 02:46 PM
02/14/20 02:46 PM
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Joined: Dec 2004
Posts: 2,362 Wheatfield, NY
Cuda340
top fuel
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top fuel
Joined: Dec 2004
Posts: 2,362
Wheatfield, NY
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I think you'll want the smallest bore size that you can find. Might be 15/16 but I haven't looked for a while. If you are looking for a 15/16" bore size master a 1975 Duster With Power Disc brakes uses a 15'16" bore.
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Re: Power to Manual Brakes - Master Cylinder Bore Size
[Re: Cuda340]
#2751152
03/12/20 06:24 AM
03/12/20 06:24 AM
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Joined: Jan 2003
Posts: 17,916 Akron, Ohio
ProSport
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 17,916
Akron, Ohio
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I bought the MC that DrDiff modifies and sells for my 4 wheel disc's. I believe it is 15/16. Works great, I have a distribution valve but no proportioning valve.
1970 Challenger, all aluminum 528 Hemi, HDK suspension, Tremec 5 speed manual
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