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Technical Need help building a pivot (mat'l suggestions)...

Discussion in 'The Hokey Ass Message Board' started by JK, Jan 12, 2019.

  1. I'm trying to make a pivot rod for an underfloor brake system to move the MC & booster further outboard to make room for the exhaust. I need the pivot to look like a scaled down clutch z-bar. I have some materials in mind but I think I'm building it too big (3/4" Borgeson splined steering rod, UHMW plastic liner & 1-1/2" outer pipe, etc). One arm will be 2-1/2" long and welded to the pivot & one will be about 2-3/4" long and welded to a splined collar. I don't really think there will be tons of torque applied to the rod (normal braking & emergency braking). Can I get away with building this thing out of say a hardened hitch pin or a grade 8 bolt? Will the cutting & welding weaken these? Anybody have any material suggestions?
     
    chryslerfan55 likes this.
  2. For a brake system, too large is good....
     
    Boneyard51 likes this.
  3. metalman
    Joined: Dec 30, 2006
    Posts: 3,273

    metalman
    Member

    I'm confused. What part are you using the hitch pin or bolt for? Also, the UHMW liner, not familiar with what that is, something to use as a bushing for the shaft to rotate in?
     
  4. golferforpar
    Joined: Nov 7, 2009
    Posts: 34

    golferforpar
    Member
    from Wisc

    UHMW (ultra high molecular weight polyethylene) is an extremely tough plastic with high abrasion and wear resistance. The versatility of polyethylene has made it a popular plastic for countless industrial applications that require durability, low friction, and chemical resistance. Applications include UHMW wear strips, chain guides, and marine dock fender pads.

    Very easy to machine, available in sheet, rounds, squares, many different shapes.
     
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  5. Yup, using the UHWM plastic as a bushing between the rod and the tube and the hitch pin as a rotating unit with arms welded to it. Basically going from linear motion to rotational motion and then back to linear motion.
     
  6. nugget32
    Joined: Aug 21, 2011
    Posts: 250

    nugget32

    Grade bolt will have a safety factor of about 1000 to 1. Good choice,

    Sent from my VS500 using The H.A.M.B. mobile app
     
  7. nugget32
    Joined: Aug 21, 2011
    Posts: 250

    nugget32

  8. 6sally6
    Joined: Feb 16, 2014
    Posts: 768

    6sally6
    Member

    It ain't so much about the material as it is about your WELDS! Good solid welds with no undercut and plenty of penetration when welding will work fine. Maybe drill a hole the size of the shaft and 'insert the shaft' and then weld on both side. Think like that....try to get as close to a solid connection(like it was one piece) as you can.
    You can do it.
    6sally6
     
  9. i have a professional welder who can do the final welds for me. I was just going to tack all of it together and let him finish weld.
     
  10. goldmountain
    Joined: Jun 12, 2016
    Posts: 1,034

    goldmountain

    I suggest that you check out a Dodge Colt from around 1990 made by Mitsubishi as far as brake linkage goes. They have the master cylinder and brake booster on the right side for their domestic market and made linkage to switch it over to the left for export over here.
     
  11. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 4,719

    Ebbsspeed
    ALLIANCE MEMBER

    Welding on both ends would require the unit be assembled to make the final weld. That's not going to play well with that UHMW bushing he's planning to use.
     
    Last edited: Jan 13, 2019
  12. gimpyshotrods
    Joined: May 20, 2009
    Posts: 16,177

    gimpyshotrods
    Member

    I have one of these:
    [​IMG]
    It is all 1/4" welded steel. Grade-8 bolt. Metal bushings on the top and bottom of the pivot tube.

    Here it is in its intended application:
    [​IMG]
     
    Last edited: Jan 13, 2019
  13. gimpyshotrods
    Joined: May 20, 2009
    Posts: 16,177

    gimpyshotrods
    Member

  14. This is a good idea but I need the inner shaft to turn. the outer shaft will have gussets welded to it and then be bolted to the frame. The inside arms will be welded to the shaft and the outside arms will be welded to a splined collar that will be pinned or have set screws holding it on. I'd also thought about drilling and tapping the outside for a bolt and washer to hold the splined shaft on.
     
  15. 6sally6
    Joined: Feb 16, 2014
    Posts: 768

    6sally6
    Member

    Guess maybe I didn't "see" the whole thing in my minds eye?!
    6sally6
     
    gimpyshotrods likes this.
  16. X-cpe
    Joined: Mar 9, 2018
    Posts: 691

    X-cpe

    Have you thought about using the top end of a steering shaft? It comes with slightly tapered splines and a threaded stub with a nut to hold the steering wheel on. That would remove any play between the splines. If you used a piece of wood dowel in the hole in the steering wheel to protect its splines and provide a place for the pilot you could use a hole saw to cut out your collar.

    With the two different length arms you are changing the travel ratio a little bit, so two things to check. Make sure the M/C bottoms out before the pedal hits the floor. The arm that pushes the rod into the M/C should be at 90* to the rod at half way through the M/C piston's nominal travel when applying the brakes.
     
  17. squirrel
    Joined: Sep 23, 2004
    Posts: 43,460

    squirrel
    Member

    this sounds like a risky way to do it. Look at the product pictured above...think about what happens when any one welded connection fails. There is backup.

    And this from the guy who runs single pot master cylinders...

    Anyways, if you can make drawings (or a prototype) of what you plan to do, it will let us evaluate it much better than just describing some aspects of it.

    You'll probably find that most OEM brake systems have a direct connection between the pedal and the master cylinder. Failure here can be a serious problem, so it's best to eliminate the "monkey motion" if possible.
     

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