Why am I getting a weird measurement for a driveshaft?

Discussion in 'Transmission and Drivetrain Tech' started by MRGTX, Mar 13, 2018.

  1. MRGTX

    MRGTX Well-Known Member

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    Hey, guys.
    I just installed my new rear axle, Hotchkis lowering springs, shocks, etc...and I'm measuring up for a new driveshaft.

    So it's a Magnum 5.9 bolted to an A904 in a Dart Sport. The rear end is a Moser 8.75" with their stamped housing with a 1350 yoke. I called Moser and the guy I talked to was fairly sure that the hosing wouldn't make a difference from the stock location.

    This forum shows people with the A904/8.75" combo getting 49" give or take shafts...I got just under 53"!

    The measurements were done with the car off the ground but with jackstands under the axle at the rear and jackstands at the front holding the car just about level. I measured from the flat/farthest forward point on the yoke to the seal...

    Any ideas?
     
    Last edited: Mar 13, 2018
  2. Dana67Dart

    Dana67Dart Most undignified way to get to Colorado!

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    Your putting it in a Dart 111" wheel base is my guess. 904 and 8 3/4 is about 52.5" with 111" WB. Barracuda with 108" would be about 3 inches shorter at about 49.5"

    These are theoretical numbers based on my research of what the books say. I have yet to mount my 8 3/4 and measure.
     
  3. MRGTX

    MRGTX Well-Known Member

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    Thanks but my Dart is a Sport so it's the same as a Duster... 108" wheelbase.
     
  4. Dana67Dart

    Dana67Dart Most undignified way to get to Colorado!

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    Just re-read. I think most length quotes are center of front U joint to center of rear U joint. that would account for some of your length difference. I don't have the slip yoke seal but you can see there is at least 2-3 inches from center of u joint to where the seal would be
    20180309_114126-jpg.jpg


    This is another members photo with the seal and the same applies
    image31-2-jpg.jpg
     
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    • MRGTX

      MRGTX Well-Known Member

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      That could explain it...I went by the Denny's diagram.

      b.gif
       
    • Dana67Dart

      Dana67Dart Most undignified way to get to Colorado!

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      I think they take into account the slip yoke and reduce the shaft length accordingly, I saw this on one shaft manufacturers website but they asked for the trans, rear and car info as well.
       
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      • davescuda

        davescuda FABO Gold Member FABO Gold Member

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        center to center of U joints thats why you are off
         
        Last edited: Mar 13, 2018
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        • Bad Sport

          Bad Sport HALF A BUBBLE OFF Staff Member FABO Gold Member

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          I have a Dart Sport 904/8 3/4, and my DS is 49" center to center on the U joint caps.
           
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          • crackedback

            crackedback FABO Gold Member FABO Gold Member

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            Gotta take the yoke into account!
             
          • jbc426

            jbc426 Well-Known Member

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            I bought a forged 1350 yoke from Mark Williams put it in with 1 inch of slide spacing for clearance and measured per Dr DIff's instructions. Sent my Yoke to Strange Engineering and got a chrome moly 3 1/2" Driveshaft with forged 1350 zerkless u-joints was drop shipped from Strange for around $300+. That's hard to beat.