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Axle swap brake issue

Discussion in '6.9L IH & 7.3L IDI Diesels' started by OREGON KID, Aug 12, 2020.

  1. OREGON KID

    OREGON KID Registered User

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    Hey guys .....
    So i swaped in front and rear 03 axles and brakes from an 250 into my 93 ...i cant figure out this issue.
    Truck is off and brake pedal is 90%....
    Then i start it and its a complete loss of all preasure.....all new calipers,rotors and lines...hard and soft have been swapped for extended stainless lines.....rabs valve bleeds clean no bubbles and thats with a vacume bleeder.....
    Any thoughts or guidence ???? Thanks
     
  2. Dirtleg

    Dirtleg Full Access Member

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    Hydroboost or Vacuum still.

    You said you swapped brakes but does that include the master cylinder as well?
     
    riphip and Thewespaul like this.
  3. u2slow

    u2slow bilge rat

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    Does it firm up with another brake application?

    Many swaps to rear disc end up with a low pedal. Calipers take more volume than drum wheel cylinders.
     
  4. MtnHaul

    MtnHaul Supporting Member Supporting Member

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    Wouldn't you need a proportioning valve or an updated MC for those axles/brakes?
     
  5. OREGON KID

    OREGON KID Registered User

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    Its hydro and when its off i have 90% power....but as soon as i start the truck its straight to the floor.....would i need to update the master cylinder?? As far as installing a proportioning valve it has rear abs so where would i tap one in.??? Do away with the rear abs ?? I wont haul much and have trailer brakes.... Honestly im just stumped...ive read others have done this swap without the issue...i dont know if it has anything to do with the recent turbo install .....thanks for the input ...
     
  6. u2slow

    u2slow bilge rat

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    What is "90% power"?

    When the pedal drops, are the brakes applied or not (i.e. truck rolls?)

    Would make the most sense to me to update the master. Ford hydroboost comes from a rear disc truck... match the components. What did you do for the intermediate pushrod between the hydroboost and master? Is it the correct length?
     
  7. MtnHaul

    MtnHaul Supporting Member Supporting Member

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    With a hydro conversion I thought the brake pedal also needed to be swapped or modified. I think u2slow is on it with "match the components". I've looked into the hydro swap using parts from the OBS era and I do recall the pedal and MC need to be swapped and I think the power steering pump needed a mod or swapped. But of course I haven't actually done the work so grain of salt and all that.
     
  8. Black dawg

    Black dawg Registered User

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    super duty master is about 1/4 inch bigger bore....
     
  9. lotzagoodstuff

    lotzagoodstuff Supporting Member Supporting Member

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    Two questions:

    Did you swap the pedal to a hydroboost brake pedal?

    Did you swap the master cylinder to something that matches the axles you swapped in?
     
  10. OREGON KID

    OREGON KID Registered User

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    I just swapped in. A new master cylinder and cured the issue.....im guessing after 1+ years of being open (brake line ends in plastic bags) the master dried out ... Replaced with complete master/booster and now solid brakes ....
    Thank you all for the guidance and advice
     
  11. jrollf

    jrollf Full Access Member

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    You'll need the propirtioning valve off the 03, they are different between disk/drum and disk/disk setups.

    On the factory 93 master cylinder it screws onto the rear port.[​IMG]

    1993 F350 Crew Cab Dually
    7.3L IDIT with a Banks Sidewinder
    ZF 5-spd manual transmission
     
  12. frankenwrench

    frankenwrench overkill is under rated!

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    Did the 03 rear end swap on my 91 250 in 2016 or 2017. I just got a 1 1/4 bore mc to replace my 1 1/16 mc and that's all. No pedal swap, no proportioning valve swap, none of it. Breaks are awesome now and my parking break works as it never had before regardless how much I tinkered with it. You will love the conversion. I know I did.
     

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