Spohn 644 - Manual (Page 2)

Setting Pinion Angle
There are two angles to deal with:
1) Driveshaft angle
2) Pinion angle
You subtract pinion angle from driveshaft angle to get TRUE pinion angle
Here's how you do it:
First, had you measured your stock drive shaft angle and pinion angle you would have
calculated a 0 deg. TRUE pinion angle. This is how all cars come from the factory.
Using an angle finder place it on the underside of the driveshaft and record the angle
indicated.
Next, place the angle finder under the flat surface of the pinion yoke (this surface is parallel
with the pinion shaft) and record the angle indicated. Record both angles from the driver’s
side of the car. On the driveshaft anything to the left of 0 is positive, on the rear end anything
to the right of 0 is negative.
Subtract the pinion angle from the driveshaft angle. The result is "TRUE Pinion
Angle".
In order to apply pre-load you need negative TRUE pinion angle. Adjust so that the front of the
pinion goes down; continue to check each angle until the pinion angle is more degrees down
than the driveshaft angle.
We recommend –1 degrees on a mildly modified daily driven car. For high horsepower
applications we have gotten the best results with –2 degrees. There is no reason to run more
negative than that, it will actually hurt your performance because it will induce driveline bind.
Here's a tip. When adjusting for your TRUE pinion angle, count the number of flats (or the 1/6
of a turn) as you turn the adjusting hex, to know how many it takes to adjust 1 degree of
negative TRUE pinion angle and in what direction (clockwise, or counter-clockwise). Once you
know that, then adjusting the arm at the track or before a race will take almost no time, and
no angle finder will be needed.
Adjusting your Spohn Arm: You adjust the pinion angle by turning the pinion angle adjuster
either clockwise or counter-clockwise. As you turn the adjuster you will see the pinion nose of
the rear housing moving up/down. Moving the rear housing's pinion nose down will give you
more of a negative pinion angle degree, and up will give you more of a positive pinion angle
degree.
You will quickly learn that it does not take many turns to adjust the angle by several degrees,
so go slowly and check your angles often.
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