Pinion angle help needed.

Suspension, Steering and Chassis

  1. Kent mosby

    Kent mosby FABO Gold Member FABO Gold Member

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    My 1973 scamp is almost ready to go, or so I thought. I have a completely rebuilt 512 RB, 727 trans, 8 3/4 shortened rear. SS springs. Competition engineerings drag shocks..
    During hard acceleration there is not much vibration but cruising at 3500 rpm, 72 mph there is tremendous vibration coming from the driveline.

    My measurements are relative to gravity on a lift. The transmission output shaft is pointed down 1-2 degrees. The pinion is pointed down 7 degrees as well. I understand that the rear end pivots up during hard acceleration and that may be why I do not get the vibration.
    View attachment 1715533907

    Is the only way to make this better to redo the perches? Can shims help this?

    unnamed.jpg
     
    Last edited: May 23, 2020 at 8:06 PM
  2. mopowers

    mopowers Well-Known Member

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    You're only a couple degrees off. Shim it and be done with it.
     
  3. pishta

    pishta I know I'm right....

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    your way off! if your trans CL is -2 down..your pinion should be like -1 down so under acceleration is my go up to +2, and that would be perfect parallelism to output shaft.
     
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    • mopowers

      mopowers Well-Known Member

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    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

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      Seems to me the pinion should be damn near zero (level) so when it comes up it matches the tailshaft.
       
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      • Tooljunkie

        Tooljunkie King of cobble/master of the broken bolt FABO Gold Member

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        I use an app, its a pain,but i level driveline with my jack under the diff, then point diff to get the number i need

        F307EC03-7803-4EE0-880E-73C8EAF890AE.png

        FE96EA6B-5181-4348-A0F5-C7BF6021B3A8.png
         
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        • Kent mosby

          Kent mosby FABO Gold Member FABO Gold Member

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          @Tooljunkie very nice app. Thanks

          Would using a 6 degree shim be good to get me into a working setup? That would get me to -1 relative to ground but more important 6 down relative to the driveshaft. which is what the "Book"says to be.
           
        • DoctorDiff

          DoctorDiff Well-Known Member

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          Your pinion angle is 9 degrees negative. I consider 4 degrees negative, maximum.
           
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          • famous bob

            famous bob mopar misfit FABO Gold Member

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            Too much when not under load ---------------
             
          • teringer

            teringer ase master hall of fame FABO Gold Member

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            I would raise trans to 1 plus you may not be changing your pinion angle much depending on your rear suspension ,also check fan ect after shiming
             
          • AJ/FormS

            AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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            Easy to prove;Feed it gas and brake simultaneously, while traveling in the vibration zone.
            I run about your angles but with softer springs, and a 367 with a manual-trans. It has no vibration traceable to the pinion angle..
             
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