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Technical Recommend master cylinder with 7/8" bore?

Discussion in 'The Hokey Ass Message Board' started by Greasyman, Mar 17, 2015.

  1. Greasyman
    Joined: Oct 23, 2010
    Posts: 165

    Greasyman
    Member

    I need more brake pressure and want to switch from a 1" bore to a 7/8" bore. I looked around a bit and it seems most in that size are for modern Japanese cars. Anyone know of any American style double reservoir master cylinders with that size bore? Thanks.
     
  2. Road Angels
    Joined: Mar 2, 2015
    Posts: 125

    Road Angels

    Might have better luck with a 3/4, bore Iam guessing no power asst.? go to rock auto you might find what you need just dont buy it from them
     
  3. Road Angels
    Joined: Mar 2, 2015
    Posts: 125

    Road Angels

    Dont know what you want to spend but wildwood has them $300 apply your own grease, also if you have drum in back you may have to change your P valve to prevent lock up, less you got some really big tires back there
     
  4. ratman
    Joined: Jun 15, 2006
    Posts: 423

    ratman
    Member


  5. mohr hp
    Joined: Nov 18, 2009
    Posts: 262

    mohr hp
    Member
    from Georgia

    Disc/drum '76 Monza manual, for disc/disc you can use 70's Corvette manual
     
  6. I recently found this info on another forum. HRP


    Here is some info on master cylinder with "constant" of 6 to 1 pedal ratio and 100 psi being applied.
    3/4" master cylinder = 1359 psi
    13/16" master cylinder = 1158 psi
    7/8" master cylinder = 998 psi
    15/16" master cylinder = 870 psi
    1" master cylinder = 764 psi
    1-1/8" master cylinder = 603 psi
     
  7. I think my brother's Morris used a vega 7/8th" master cyl ....or it could have been an opel unit. Had enough pressure to get stopped but damn! The pedal went almost all the way to the floor every time. Was a dual chamber, disc/drum unit.
     
  8. ago
    Joined: Oct 12, 2005
    Posts: 2,199

    ago
    Member
    from pgh. pa.

    Good info from HRP!
    I used a Chevy Monza M/C I believe is 7/8"
     
  9. 54fierro
    Joined: Jul 6, 2006
    Posts: 493

    54fierro
    Member
    from san diego

    I used a 7/8" master cylinder on my 54. It was the same bore as the original one pot master.
    It is listed for an 81 Dodge Aries and takes standard 3/16" brake line fittings, no adapters necessary. It is best to buy it new so it come with the reservoir, most of the time the reman cylinders dont have them. Autozone shows the for under $30. Cesar
    [​IMG]
     
    deluxester likes this.
  10. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,737

    V8 Bob
    ALLIANCE MEMBER

    I would not use a master cylinder for any FWD diagonal-split system, like the "K" car platform one above, on a RWD vertical F/R split system. Each half of this master feeds just one small front disc caliper and one small rear drum wheel cylinder, and will have marginal fluid displacement for larger vertically split brakes.
     
    Last edited: Mar 17, 2015
  11. 54fierro
    Joined: Jul 6, 2006
    Posts: 493

    54fierro
    Member
    from san diego

    I am running drums on all four corners on my car so volume may not be an issue in my situation.

    Do you think the ones Wilwood sells in this style are different internally than the stock Chrysler MCs?
     
  12. Any chance it would be easier to change the linkage?

    Charlie Stephens
     
  13. ago
    Joined: Oct 12, 2005
    Posts: 2,199

    ago
    Member
    from pgh. pa.

    The Chevy Monza M/C is a front disc, rear drum 7/8"
     
  14. Greasyman
    Joined: Oct 23, 2010
    Posts: 165

    Greasyman
    Member

    Thanks for everyone's help. I went with the Monza unit.
     
  15. 3spd
    Joined: May 2, 2009
    Posts: 542

    3spd
    Member

    I think you meant 100lb not psi, this is actually an easy calculation; its just the force on the pedal times pedal ratio cylinder divided by the area so for a 7/8" bore master it is: (100lb x 6)/(pi*0.4375^2) = 997.9 psi.

    Also a lot of fox body Fords came with 7/8 bore master, according to Rockauto.com 79-81's did for future reference.

    Ryland
     
  16. Greasyman
    Joined: Oct 23, 2010
    Posts: 165

    Greasyman
    Member

  17. Greasyman
    Joined: Oct 23, 2010
    Posts: 165

    Greasyman
    Member

    So I just picked up the Monza master cylinder I ordered. Much to my surprise it has a very shallow hole in the piston, the kind that is supposed to be for power brakes. I thought just about all power brakes used a bore size larger than 1".

    I've noticed that there is rarely any mention of whether a m/c is intended for power or manual, even when ordering they don't ask. I've been warned that if I use the piston with the shallow hole, my pushrod will fall out and I'll die, so I'd think this would be a critical spec. Now I don't know what to do. Maybe I'll try drilling the hole deeper.
     
  18. fordcpe
    Joined: Nov 4, 2005
    Posts: 636

    fordcpe
    Member

    65 to 67 ford Mustang in mine. You can get manual( no booster) drum/drum or manual(no booster) disc/drum it has the deep hole in the piston.I think it is 7/8" but might be 15/16 some check that out.
     
  19. 54fierro
    Joined: Jul 6, 2006
    Posts: 493

    54fierro
    Member
    from san diego

    The 80 Ford Fairmont also uses a 7/8 bore master. The hole on the piston looks deep in the Autozone website.

    Part Number: NM1764
    Weight: 7.28 lbs
    Warranty: Limited Lifetime
    Notes: With reservoir
    Installation Hardware Included: Yes
    Item Grade: OEM Standard
    Master Cylinder Bore Diameter (in): 0.875
    Master Cylinder Color / Finish: Metallic
    Master Cylinder Material: Cast Iron
    Master Cylinder Port Sizes: Primary 0.5"-20 , Secondary 0.437"-24
    [​IMG]
     
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  20. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,737

    V8 Bob
    ALLIANCE MEMBER

    All of the late '60s-'80s power brake Ford masters I use or have seen have a deep counter bore, but is probably not be true for all makes.
    Some boosters have a supported/guided push rod and can safely use a shallow counter bore. Some manual systems may have push rod angularity issues and need to keep the retained push rod shallow to prevent any binding in the bore.
    In most cases, the power and non-power master bores for a given vehicle remains the same.
    If you're going to use a unrestrained manual push rod, you need a deep counter bore.
    And, no, don't be drillin' on the primary piston! :eek: Find the proper master. :)
     
    Last edited: Mar 18, 2015
  21. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,737

    V8 Bob
    ALLIANCE MEMBER

    The first Mustang dual master was '67, and all '67-'72 all had a 1" bore.
     
    Last edited: Mar 19, 2015
    deluxester likes this.
  22. 39-2dr
    Joined: Jun 4, 2007
    Posts: 284

    39-2dr
    Member
    from MISSOURI

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