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Technical Master Cylinder push Rod maximum length ?

Discussion in 'The Hokey Ass Message Board' started by kyotb8, Feb 5, 2016.

  1. kyotb8
    Joined: Aug 19, 2011
    Posts: 56

    kyotb8
    Member

    Need some advice on the brakes again. Best place to put the master because of a lot of reasons is at the rear of the cab. I can access it there by moving the seat up, but the length of the rod from the pedal to the master would need to be 35-36 inches !!!! What's some opinions on that ? And if the length would work, how big should the tube/rod be ? 1/2" round tube ? 1/2" square ? Or bigger ? The car is the same old 39 Plymouth pickup .
    Main reason to consider this location is that if I put it in front of the seat, I've got to have a raised door for access, that would stick up about an inch above the floor, and foot room is already tight. Thanks in advance for reading and letting me know what you all think.
     
  2. oj
    Joined: Jul 27, 2008
    Posts: 6,454

    oj
    Member

    In the drag cars we'd have very long pushrods and made them from 5/8ths chromemoly tube with 'weldnuts' in each end to thread 3/8ths rods to return to factory size, at midpoint we'd add a loop the tube would pass thru as a retainer to the rod couldn't possibly drop out. The loop is loose fit, like a big eyebolt, but we'd make then kinda fancy.
     
    stimpy likes this.
  3. kyotb8
    Joined: Aug 19, 2011
    Posts: 56

    kyotb8
    Member

    Thanks for that idea ! I thought that something bigger than 1/2 would be best ! And the loop is a great idea ! Thanks again !
     
  4. krusty40
    Joined: Jan 10, 2006
    Posts: 869

    krusty40
    ALLIANCE MEMBER

    oj has it right. However, I'd use 5/8 or 3/4" mild steel seamless tube with an .090 or 0.120 wall, as it will be easier to acquire. With luck, you'll be able to find a "drop" of the needed length at your friendly local steel warehouse or racing chassis fab shop. You might also find a thicker wall tube that could be threaded, rather than welding threaded nuts on the ends. The safety loop is important.

    vic
     

  5. aaggie
    Joined: Nov 21, 2009
    Posts: 2,530

    aaggie
    Member

    The length would not be as much a problem as the diameter. After you have your mounting point established measure the length needed and pick a rod or tube stiff enough to resist bending. The loop to support the middle sounds like a good idea but not something as tight a fit as a Heim joint. There has to be a loose enough fit to allow the arc motion of the rod.
     
  6. dreracecar
    Joined: Aug 27, 2009
    Posts: 3,476

    dreracecar
    Member
    from so-cal

    Plenty of chassis suppliers back there so for 3' of cm tubing and 2 threaded ends, you are in at under $25. 5/8 would be the absolute minimum for that length, but would go with 3/4 x .058 wall for a safety margin and the fact that most threaded ends are made for that wall tubing.
     
  7. kyotb8
    Joined: Aug 19, 2011
    Posts: 56

    kyotb8
    Member

    Thanks much for the suggestions ! I can get started making this work in the morning ! Appreciate all the input from everyone !
     
  8. patterg2003
    Joined: Sep 21, 2014
    Posts: 864

    patterg2003

    Wicks Aircraft or Aircraft Spruce can sell you any diameter , thickness & length of 4130 chromoly tube suitable for a push rod. 4130 chromoly is super strong & is commonly used by aircraft home builders. Same material used for NASCAR roll cages. Best is to TIG or Oxyacetylene gas weld chromoly. If there is a choice stay away from Chinese tube & go with American or German.

    https://www.aircraftspruce.ca/catalog/mepages/4130tubing_un1.php
    http://aircraftproducts.wicksaircra...gles/4130-round-tubing?&pagenum=2&pagesize=50

    Glenn
     
    Last edited: Feb 5, 2016
  9. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,264

    gimpyshotrods
    ALLIANCE MEMBER

    Preferably not extending past either bumper.
     
    shawnsauto1 and oj like this.
  10. woodiewagon46
    Joined: Mar 14, 2013
    Posts: 2,269

    woodiewagon46
    Member
    from New York

    Would you consider using a linear bearing for support on each end or the master cylinder end?
     
  11. dreracecar
    Joined: Aug 27, 2009
    Posts: 3,476

    dreracecar
    Member
    from so-cal

    NASCAR cages are made out of mild steel DOM material not moly
     
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  12. seb fontana
    Joined: Sep 1, 2005
    Posts: 8,444

    seb fontana
    Member
    from ct

    I would put an idler arm near the master to support the weight of the push rod..
     
  13. kyotb8
    Joined: Aug 19, 2011
    Posts: 56

    kyotb8
    Member

    Not sure I know "linear" bearing ? Explain for this new bee please ? Am I just not getting this ????
     
  14. I used 5/8" steel rod about 22" long to put my brake pedal bracket where it needed to be and the booster/master cylinder on the crossmember of my '29 AA, just under the seat. It forces me to install a remote filler for the m/c, but at least I have room now to put it all together.
     

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  15. woodiewagon46
    Joined: Mar 14, 2013
    Posts: 2,269

    woodiewagon46
    Member
    from New York

    kyotb8, a linear bearing is used to allow a shaft to run back and forth. It will allow your MC pushrod to travel from your brake pedal to the master cylinder with some support. Go on to the McMaster Carr website and enter Linear bearing and you will see what it is.
     
  16. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,264

    gimpyshotrods
    ALLIANCE MEMBER

    It is a tube (the outer race), lined with ball bearing in a special cage.

    [​IMG]
    The shape of the race allows the bearings to move in a loop. This facilitates something moving through the bearing, in a straight line.
     
  17. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,264

    gimpyshotrods
    ALLIANCE MEMBER

    You can use a mounted tube, with a Delrin sleeve inside of it, too. I have done than. Seems to work fine.
     
  18. fadt
    Joined: Oct 3, 2010
    Posts: 128

    fadt
    Member
    from England

    If I remember the push rod is around 3 foot long. Hope it helps. I used a bit of tube to 'contain' the rod. The pedal end of the rod will move in an arc (unless you put more joints in it) so you cant have a fixed support point along its length, unless it can also move up and down.

    brake lines (17) (2015_11_13 11_07_31 UTC).JPG

    brake lines (42) (2015_11_13 11_07_31 UTC).JPG
     
  19. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,657

    Rusty O'Toole
    Member

    Have you thought of mounting it on the firewall with a suspended pedal?
     
  20. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,264

    gimpyshotrods
    ALLIANCE MEMBER

    That's probably what I would do.
     
  21. kyotb8
    Joined: Aug 19, 2011
    Posts: 56

    kyotb8
    Member

    Well I learned something new today ! Never saw a bearing like that before ! Thanks
     
  22. kyotb8
    Joined: Aug 19, 2011
    Posts: 56

    kyotb8
    Member

    Yes have and am considering that ! Might be easier, but just like the idea of not seeing the master ... I'm thinking ...
     
  23. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,264

    gimpyshotrods
    ALLIANCE MEMBER

  24. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    I have underfloor pedals on my 27 going to a 66 Chevy pickup truck dual master cylinder (one side brakes the other side clutch) I made pushrods that are about a foot long out of round tubing with bungs welded into each end. On one side I have rod ends that go to the pedals and on the other side I have a cut off bolt that I am using as the pushrod into the master cylinder. That way, I can turn the rods out of the threaded bungs for adjustment.

    Been that way for over 25 years with a very stiff clutch and no problems.

    Don
     

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