Newer model 40 front axle with disks

Discussion in '40- & 55-Series Tech' started by Jon in NC, Oct 26, 2005.

  1. Jon in NC

    Jon in NC

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    Will a newer 40 front axle bolt up to my '71? I want the disk brakes. I'm not into any hard wheeling (yet ?) mostly street and dirt roads. Just tired of double pumping my drum brakes and having to steer hard to one side or the other.
     
  2. Landpimp

    Landpimp GOLD Star

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    axle ratios will not be the same, late is 3.73.
     
  3. Jon in NC

    Jon in NC

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    So I'll just have to change gears in the front, right? Can I just take out mine and put them into the newer axle?
     
  4. 2badfjs

    2badfjs

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    yup, i've swapped diffs back and forth between 40's and 60's
    and plan on doin it again :D
     
  5. Landpimp

    Landpimp GOLD Star

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    will also need the square u bolt for the PS of the axle.

    i would think that the side gears on the diffs would need to be swaped......but not real up on that kinda stuff.
     
  6. woody

    woody unhelpful spotter Staff Member Admin

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    you have two options really....

    First is to remove the installed axle, disassemble both axles completely and swap the center sections, putting your drum center in the disc housing...while yer at it, spend $100 on a knuckle rebuild kit so you don't have to do that again....hell, it's all apart anyways. Then reinstall...LOTS o work...

    Second option is to leave your existing housing installed, not deal with u-bolts or d-shaft flanges or any of that, and simply do a knuckle-out swap between the two housings. Same $100 knuckle rebuild kit, and less overall work. You MAY (and should) grind the fish-mouth opening of the housing once it's apart to make room for any future longfield/minibirf upgrades/repairs. Otherwise, it's a matter of removing it from the new housing and installing on the old housing....trunions are identical, knuckle kits are identical, all the disc brake stuff upgrades easy enuf.

    edit:
    side gears are both 30-spline, birfs change from old POS coarse to fine, but inner axles are identical so keep those for spares. You'll use EVERYTHING from the knuckle out in the conversion, including the lockout, spindle, knuckle, discs, backing plate, etc....strip the existing, and lay the replacement next to it and start moving stuff over.

    edit2:
    you WILL need to deal with brakes a little....if you opt to swap housings, I'll wager you need all new hard lines, since IIRC the 71 will attach from the DS and the later stuff attaches to the frame at the PS...IIRC. Another good reason to not swap the actual housing. Also, you need to remove the residual valve in the master for the front circuit, since you have a drum axle installed....little piece of plastic, takes 5 minutes....see the tech links.

    Balance is a piece of cake, should be a 2 hour project :D
     
    Last edited: Oct 26, 2005
  7. honk

    honk

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    WTF?

    Axles from '75, '76, '77, and '78 will have the same 4.10 ratio gears that your '71 has. You can basically just roll one out and roll the newer one in.

    The driveline flanges, brake line routing and configuration will be different but if the '78 or earlier disc brake axle has coarse pinion splines you could just use your old one. Some early '78s still came with the coarse spline pinion but it's a rare thing so IF you get a '78 you may need to adapt and use a newer front driveshaft as well.
    Best to find one of the other disc axles to use.
     
  8. woody

    woody unhelpful spotter Staff Member Admin

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    75 will be drum still

    79-80-81-82-83 will be 3.7....and have better birfields....76-78 are "morph" fronts and personally, I would stall for a later one...commonality...
     
  9. Jon in NC

    Jon in NC

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    So I should look for a 79 - 83 and do the work to match the gears, correct?
     
  10. woody

    woody unhelpful spotter Staff Member Admin

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    76-78 is still disc....the steering arms and knuckles are the "only" difference for what you need...but given the choice, I'd stall for either a 79+ or a minitruck axle....

    IMO...I tend to be hard on equipment, and having something with "commonality" makes more sense to me....
     
  11. Yoda

    Yoda

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    I did a 79 axle into my 71. Did the knuckle kit, did the new lines on the axle to match the tubing on the truck, swapped the gears from the 71 into the 79 housing.
     
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