A Body Disc Brake Swap 101

Brakes for your Classic Mopar

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  1. snomopar

    snomopar junior?

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    Might I suggest in place of the pickle fork, one uses a BFH (large hammer) and hit the spindle where the tappered end of the ball joint goes through the spindle. This method also works on the tie-rod end where it also goes through the spindle and/or any tappered fit.

    I suggest loosening the ball joint nut (or tie-rod end nut) and back it out a turn or two but don't remove it before hitting the spindle. This will keep things together once the tappered fit of the ball joint breaks free from the spindle.

    In all my years at the dealer I've never had a need for a pickle fork. This also works on any small engine that has a trappered fit flywheel. I place the plastic handle of a junk screw driver between the flywheel and hammer to avoid knocking magnets loose.

    Just a thought.

    FNG - John
     
  2. 2 Darts

    2 Darts A-body Addicted

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    I've seen this on the BBP conversion when the caliper bleed valve is lower than the caliper brake hose. An air bubble forms in the caliper. It appears like the caliper has been bled, but the air in the pocket gets compressed before anything like braking action happens.

    One correction is to remove the caliper from the spindle, block the caliper piston fully retracted into the housing (I use a giant C-clamp), then hang the caliper in a way that the bleed valve is higher than the hydraulic fluid hose.

    Every time I have seen this, the caliper is mounted to the rear of centerline. It may be corrected by reversing the spindles, but I don't know for certain.
     
  3. dodge71demon

    dodge71demon Well-Known Member

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    Does the caliper go on the front or back of the spindle?
    I use to put them on the front but now I always put them
    on the back.I like the looks alot more and they work fine.
    I use the rubber brake hose from a 73 and up B body
     
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    • 7071DartGTReg

      7071DartGTReg Deceased - RIP Bruce Legendary Member

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      Great updates guys!
      I don't mention BFH Snomopar 'cause that is an advanced experience tool in my opinion -
      Newbies can REALLY screw stuff up with one!

      Real good tip 2 Darts! I forget that some people mount the Calipers in reverse.

      dodge71demon; Seems to be prefered backwards (Caliper in rear) to clear the
      Sway Bar with Factory Sway Bar Lower Control Arms.
      Just beware when mounting them this way of the bleeding issue mentioned above.

      Later,
      Bruce B.
       
    • dgc333

      dgc333 Well-Known Member

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      The 73+ disks had the caliper to the front. I have heard that with it mounted to the front on a 72 down car with a factory sway bar the caliper can it the sway bar at full lock. If you swap sides with the spindle so you can mount the caliper to the back you need to swap calipers side to side too or the bleeder winds up being lower than the hose and causes all kinds of bleeding issues.
       
    • snomopar

      snomopar junior?

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      Agreed, point well taken.

      Although it may come in handy to avoid chewing up the BJ grease boot if a rookie decides to reverse caliper location.

      The top of the spindle is real accessable but as you say, proper BFH control is a must because it is the top your banging on. swinging from the ground, the fender lip can jump right into the flight path... uh, oh.

      Great thread and I'll be referrencing when I get to the assembly list... 'still on the parts list.

      Thanks for taking the time.

      John
       
    • AnotherA

      AnotherA Well-Known Member

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      First time doing a conversion.
      I take it this is the difference between large and small ball joints?

      I'm not sure what year the larger one is off of.

      [​IMG]

      [​IMG]
       
    • 7071DartGTReg

      7071DartGTReg Deceased - RIP Bruce Legendary Member

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      Yup!
      The one on the right is LBJ '73 up.

      Later,
      Bruce B.
       
    • dodge71demon

      dodge71demon Well-Known Member

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      I do 3 or 4 of these a year for people.
      I just assumed that eveyone knows to
      keep the bleeder valves on top.Again I
      use the rubber hose from a 73 and up
      B body.I find they fit better when doing
      them in reverse.I also change the rear drums
      to b body with moser axles.Never use a BFH
      I use a pickle fork in air hammer jack hammer
      would work faster but won't fit in wheelwell
       
    • schultec14

      schultec14 Well-Known Member

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      Hi I have a V8 1970 dodge dart swinger that I recently put all new bushings in and and all new ball joints in. I converted it over to 1973 dodge dart front disc brakes and upper control arms. I had everything torn apart at the time. Now that I have it together, but not driven yet, both calipers are behind the spindles rather than being in front of the spindles like I have seen it in a few pictures now...are the spindles directional, and I NEED TO KNOW: will this throw the castor angle off?? I tried adjusting the upper control arm adjustments and it still looks like the angle of the spindles are still leaning foreward and I'm thinking it might steer like a shopping cart...and if I am wrong, and have to switch them around, what soft brake lines should I use?? and do I have to change the hard line spot where it would screw into the soft line?? Please advise!!
      Thank you,
      -ANTHONY
       
    • dgc333

      dgc333 Well-Known Member

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      The spindles can swap side to side to place the caliper either to the front or to the rear but the 73 system came from the factory with the calipers to the front. Folks mount them to the rear on the 72 down cars so the caliper will not interfer with the factory sway bar, 73's had a different mounting arrangement for the bar so it didn't interfer.

      You need to swap caliper to, the key is the bleeder must be at the top, if they are below where the hose fits then you will never be able to bleed the system completely. If you are going to have the caliper to the rear you can't use the 73 style brakes hoses, they are not long enough and will bind with the wheels at full like and will fail quickly. You will need hoses for a Volare/Aspen disk brake car.

      The upper control arm is right and left too. If the little dimple in the control arm for the rubber bumber on the frame to contact is not over the bumper then you have the control arms on the worng side.
       
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      • schultec14

        schultec14 Well-Known Member

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        Ok, thank you for the info. From what your saying, I do have it right, with the bleeder screws at the top and that they are on the back of the spindle. But what about the castor angle? When I stare at the car from the side, its like the angle of the spindle is leaning forward...which is opposite of what I would always adjust my straight axle cars to...Is that normal on these?
         
      • omahamoparguy

        omahamoparguy Well-Known Member

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        the spindles look kinda strange on the 73 up disc cars. sometimes it seems like they are leaning forward. the design makes your eyes trick you. unlike the drum spindles which are just vertical. I devised a tool to check caster. It is like a bridge that spans both ball joints and buts up against the grease zerks. this along with a cheap angle finder gives a good ballpark figure of the caster angle. Make sure your car is level when you set the caster {or at the same rake as it is when you are driving it}
         
      • Qwk87Coupe

        Qwk87Coupe Well-Known Member

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        Will any a body UCA (drum or disc) from a 73-76 work for the disc swap? I keep reading that I need the disc brake 73-76 UCA's for the larger balljoint. Do the factory drum brake UCA's 73-76 have the small or large balljoint? I just picked up a 73 Duster with drums up front. I already have an extra set of disc spindles/calipers/rotors. Just wondering if I have everything I need or if I need to find a set of 73-76 disc UCA's
         
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        • crackedback

          crackedback FABO Gold Member FABO Gold Member

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          Yes any of them should work provided they left the factory with them. There are some cars that have had stuff swapped so be careful. If the balljoint nut is 3/4 or 13/16, then it's a BBJ, SBJ is a 5/8" nut, IIRC. Memory kind of shot on this. :toothy10:
           
        • PanGasket

          PanGasket has cork sides

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          Thanks again bruce! I have this favorite'd pretty much:cheers:
           
        • rick4106

          rick4106 Well-Known Member

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          Has anyone used m body calipers on a abody . Rotors are the same and caliper brackets are the same . Took old caliper to local parts store and matched to m body 5 th ave. Looks the same , uses same pads ,hardware, cheaper and available.
           
        • needsaresto

          needsaresto Well-Known Member

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          M body brakes will bolt on. You will need all the brakes plus an A body upper control arm with big ball joint. as the M control arm is different and wont bolt to an A body. The M's did come with a large 11.75 rotor..

          As for the KH setup it should bolt right on with a lower ball joint for disc brakes.
           
        • RedFish

          RedFish Well-Known Member

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          Hitting the casting with a shop hammer will cause the tierod end to dislodge but could also cause a hairline crack in the casting. If you have a pickle fork, use it.
          The steel backing plates on brake pads are stamped out with wide open tolerences so one size fits all rough castings. I'll tap a wedge between the outer pad and the rotors center hub to force that pad upward then tap the 2 top ears down against the casting. When the pads are properly fitted to the caliper that messy blue glue is not required and the subsequent click noise does not occur.
           
        • hwp

          hwp Active Member

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          I have done the swap on B-bodys before, but this is my first A-body swap. I am lucky, as I have a 74 Duster I am swaping from. I have everything installed. I moved the dist block from the duster and spindels and upper arms. However. the sway bar on this car is after market so I had to mount the cal to the rear. Done this on B-bodys. But on the B-body conversion. I had to use a flex line off of a diplomat or something (cant remember) What is the best line to use on this type of swap. The port on the cal is now closer to the hard mount point for the hard line. and you dont want to crimp or rub the line on the tire or any part of the front end. Any Ideas?
           
        • RedFish

          RedFish Well-Known Member

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          There is supposed to be a small amount of preload on the torsion bars. Like was stated in that other thread...
          Torsion adjust bolts backed out, either end of shock disconnected
          ( I prefer to remove the lower shock bolt ), and upper arm bump stop removed. Now, with the upper arm in lowest possible position, ( loosen the strut rod bushings if necessary ) adjust finger rotated down against the adjust bolt, install the torsion bars.
          put everything back together. You can go ahead and run the adjust bolt up to about centered in the threads. Lower the vehicle to reattach shock bolt and reinstall the upper bump stop.
          All this from memory, hope I got it about right.
           
        • RedFish

          RedFish Well-Known Member

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          Actually, when the caliper is at the 11 o'clock position and the line enters the bottom of the caliper, The flex hose is routed diagonally across in front of the shock.
          When the calipers are positioned at 1 o'clock and the line enters the bottom ( as it should ) the flex hose could be stretched at full turn. Others have suggested a longer hose from M-body.
          First time I did this swap was back in the 80s. No internet help then. I used the correct a-body hose and carefully adjusted the bend in the short metal portion of it just enough to prevent stretch and not rub the wheel.
          My mopar mentor suggested I reroute the cars hard line to meet the retainer tab from the top , then attach the line from the bottom. That probably would have worked too. Rerouting those metal lines ain't easy though.
           
        • twofosho

          twofosho Well-Known Member

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          In addition to getting the correct caliper brackets for the size rotor you want to run, you also want to make sure you have the correct bracket for the type of caliper (either slider or pin type) you'll be using. Good reason for the first timer to get the complete assemblies (upright, rotor, caliper bracket, caliper assemblies, etc.) from a donor car, then replace the worn out stuff with new that matches the old.
           
        • sledger46

          sledger46 Well-Known Member

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          Free bump with a tid-bit of information. If you are converting from 9" drums to discs and you are sourcing most of your parts new, don't forget to pick up the bolts that are used to mount the lower ball joint to the spindle. The bolts used for the 9" spindles are way too small.
           
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