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    Results 1 to 3 of 3
    1. #1
      Join Date
      Jul 2008
      Location
      BATON ROUGE
      Posts
      133
      Country Flag: United States

      4 link geometry change with pinoin angle change

      Try to address a vibration in a friends car we found the pinoin angle to be 3 deg down when it needs to be around 3 deg up. When changing the angle the mounting points on the housing change by 1/2" or so. the upper bracket moved back and down causing the angle of the upper links to be in the wrong direction so we will cut them off and redo them. but the lower brackets moved about 1/2" in front of the axle, the easy fix is to adjust the trailing arm length by 1/2" or do i need to cut these off too and redo them. not sure what effect it has on the geometry by this mounting point moving in front of the axle.

      Tim B.


    2. #2
      Join Date
      Oct 2009
      Location
      New Derry, PA
      Posts
      1,265
      Country Flag: United States
      Tim,
      If this is a drag race type 4 link, keep in mind that they are designed for the pinion to be at 0deg with the rear suspension loaded on launch. They typically do run 2-3 deg down angle, as anti squat reaction will allow the pinion to rise about that same amount. Most drag chassis are designed to run the engine/trans level (0deg trans angle), so everything evens out on launch.

      Some pics of the suspension setup would help.

      Ray Kaufman - Wyotech Chassis Fab and High Performance Instructor. Words of Wisdom from an old master... at Asylum Custom Interiors website

    3. #3
      Join Date
      Mar 2012
      Posts
      38
      Country Flag: United States
      I'm with Ray. 3 degrees up pinion angle is not something you see generally, as the pinion rises during torque application. What is the exact application? Also, it would help to know exactly how you are measuring pinion angle. I've found that there are some misconceptions as to what pinion angle really is. There is some point of contention here, but Jerry Bickel and Rick Jones(two of the very best chassis fabricators on the planet) will tell you PA is the difference between the engine/trans centerline and the face of the pinion. Whereas the common method of measuring has you measuring the difference between the driveshaft and the pinion. There can be a BIG difference there, depending on the cam height of the engine and the angle relative to the ground .

      As far as geometry goes, changing those pickup points to the extent you are talking about does effect geometry. A typical pionion angle change of a degree or two on an optimized setup wouldn't to the extent that 99.9% of the people would notice, though. Where the pickup point is in relation to axle centerline, both vertical and horizontal, changes the amount of force applied to the lower bar. Also, changing the spread of the pickup points changes the way the chassis works the shock and spring. There are so many variables, we'd really need to know your intended usage.
      Shane Hill
      90 Mustang LX with 4.6 4v and 105mm turbo 7.72 at 194mph on drag radials
      65 Mustang- MTF C6 ifs, Torque Arm, Watts Link, Ridetech shocks, Boss 302 Coyote + T56



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