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Bench bleeding a master cylinder

Discussion in 'Early CJ5 and CJ6 Tech' started by speedbuggy, Mar 14, 2006.

  1. Mar 14, 2006
    speedbuggy

    speedbuggy Looking for a Jeep now

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    I am adding Herm's dual res m/c this weekend and the only real question I have for now is:

    Do I need to bench bleed the new m/c and if so, how do you do that?

    TIA

    Oh wait- question #2:

    what about the brake light switch on my old m/c...will it convert?

    TIA
     
    speedbuggy, Mar 14, 2006
    #1
  2. Mar 14, 2006
    lynn

    lynn Time machine / Early CJ5 HR Rep Staff Member

    Huntingdon PA
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    Always bench bleed a new MC.

    http://www.misterfixit.com/brakbld1.htm
    (Lots of other results on Google "Bench Bleeding Master Cylinder"... this was just the first one ;) :D )

    Don't know about the switch, mine isn't on the MC.
     
    lynn, Mar 14, 2006
    #2
  3. Mar 14, 2006
    Mark Mann

    Mark Mann Kermit

    Huntsville, AL
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    Yes it should be bench bled. As I recall you fill with brake fluid, pump the piston until air stops bleeding out of ports- Wait some length of time (cannot recall how long, maybe 30 - 45 mins) and repeat process. I am sure someone else has a better recolection of this procedure. As for question #2, no idea.

    MM :flag:

    I see that Lynn responded in the time that I was answering.. You're all set!
     
    Mark Mann, Mar 14, 2006
    #3
  4. Mar 14, 2006
    speedbuggy

    speedbuggy Looking for a Jeep now

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    Thanks guys. Bench bleeding will be done.

    What about the switch? Anyone experience this yet?
     
    speedbuggy, Mar 14, 2006
    #4
  5. Mar 14, 2006
    dohc281

    dohc281 It is what it is.

    Laurel Springs, N.J.
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    I have one of Herm's dual mc waiting to be installed and he told me to run a line off of the mc and put the mc switch in it. Since I'm not ready for the install I haven't worried about it but I would call him and get the particulars, also then I'll have you for back up when I'm ready to do mine.R)
     
    dohc281, Mar 14, 2006
    #5
  6. Mar 14, 2006
    termin8ed

    termin8ed I didn't do it Staff Member

    Mason, MI
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    Don't have the conversion, but my 68 with the dual mc has the brake switch inline going to the back. Think some years they put one on the front and back lines. So whatever is easiest. front or back.
     
    termin8ed, Mar 14, 2006
    #6
  7. Mar 14, 2006
    speedbuggy

    speedbuggy Looking for a Jeep now

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    Can I use the original switch?
     
    speedbuggy, Mar 14, 2006
    #7
  8. Mar 14, 2006
    termin8ed

    termin8ed I didn't do it Staff Member

    Mason, MI
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    Your old one is the single cyl right? You "should" be able to reuse the switch. Just get a T fitting that will go inline to the brake lines and let you T off with the switch. Make any sence? in fact, if you need it, I probably have one of the old switchs(and T's) from that 69 I tore down. I can send it off to you tomarrow if you want.
     
    termin8ed, Mar 14, 2006
    #8
  9. Mar 14, 2006
    speedbuggy

    speedbuggy Looking for a Jeep now

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    Yep, single cyl. Switch works now, just wasn't sure how to make it work with the new set-up. Sounds easy enough, though.
     
    speedbuggy, Mar 14, 2006
    #9
  10. Mar 15, 2006
    66cj5

    66cj5 Jeep with no name

    NorthWest Indiana
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    parts 71 has 2 switches (front/rear) mounted in 't' fittings on the respective brake lines. when I used herm's kit, i only added the rear switch as i was too lazy to add the front one.
     
    66cj5, Mar 15, 2006
    #10
  11. Mar 15, 2006
    w3srl

    w3srl All-around swell dude Staff Member

    Port Orange, FL
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    The stock switch will work, it will screw right into a T fitting.

    For bench-bleeding I found it easiest to just buy a short piece of pre-fabbed brake line and cut it in half. screw each end into a brake lin eport on the MC and then bend the tubes up and around so that the ends will be up and inside the reservoirs, below the fluid level. That's important so that you don't kep sucking air up ino the MC when you release the piston. Once the bubbles are gone, you're good to go!
     
    w3srl, Mar 15, 2006
    #11
  12. Mar 15, 2006
    mruta

    mruta I drank with Billy!

    Downers Grove, IL
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    I'd like to add that it's a good idea to use a thick wooden dowel rod or a cut off broom stick for bench bleeding. I've seen a few master cylinders first-hand that were supposedly "bad" from the factory because someone used a screwdriver (or other metal object) for bench bleeding and scratched the bore.
     
    mruta, Mar 15, 2006
    #12
  13. Mar 15, 2006
    speedbuggy

    speedbuggy Looking for a Jeep now

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    I was thinking I could use the pushrod from the old m/c. That should work, right?
     
    speedbuggy, Mar 15, 2006
    #13
  14. Mar 15, 2006
    mruta

    mruta I drank with Billy!

    Downers Grove, IL
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    Yup.

    Just be careful and make sure the pushrod stays centered in the piston inside the bore. It's not difficult, but it could easily be overlooked. It's easy to make a leaker out of a master cylinder by scratching the bore.
     
    mruta, Mar 15, 2006
    #14
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