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The Guide to
Pinion Angles
- Here is guide to checking the
relative angle between the centerline of the pinion
gear in the rearend and the center line of the
driveshaft. This is known as pinion angle.
- Pinion angle is important due
to the forces at work in the rearend and rear
suspension of a rearwheel drive vehicle. As power is
applied to the rearend via the driveshaft, the
pinion gear tries to climb the ring gear. This
causes the rearend housing (along with the pinion
gear) to rotate about the axles' centerline. The
optimum relationship between the pinion gear and
driveshaft is when they are perfectly aligned. In
order to achieve this under power, you much have
some angle built into the setup when the vehicle is
at rest and not under any power.
- The typical leaf spring rear
suspension will need 5-7 degrees of negative angle.
A ladder bar or 4-link setup is much more rigid and
therefore usually only needs 1-3 degrees. You never
want the rearend setup with positive pinion angle.
This is when the yoke of the rearend is tilted
upward more than the driveshaft. This can lead to
binding of the u-joints and will hurt traction and
break driveline components.
- To check the pinion angle,
the vehicle needs to be sitting with its weight on
the tires, as it would be normally. For the best
accuracy, place weight in the driver's seat to
simulate the driver. An angle finder can be bought
from places such as Sears for about $10. Begin by
measuring the angle of the driveshaft and writing it
down. Then remove the driveshaft from the yoke (no
need to totally remove it and spill tranny fluid
everywhere) and place the angle finder on the end of
the yoke. The angle from vertical will be equal to
the angle of the centerline of the pinion gear to
the horizontal. If the driveshaft was angled upward
(it would be rare to find one that isn't) and the
rearend is nose down (not always the case, so be
sure you know which way its positioned), just add
together the two angles you measured. For instance,
if the driveshaft is 2 degrees up from level and the
pinion gear is 3 degrees nose down, then you have 5
degrees of pinion angle. If the rearend is nose up
and its angle is less than the angle of the
driveshaft, subtract the rearend angle from the
driveshaft angle. If the angle of the rearend is
steeper than that of the driveshaft, subtract the
angle of the driveshaft from that of the rearend to
see how much positive pinion angle you have. For
example, if you have a rearend angle of 5 degrees
from vertical nose up and the driveshaft is angled
up at 3 degrees, you have 2 degrees of positive
pinion angle. If this was a leaf spring car, you'd
need to change the angle by 7 degrees to get 5
degrees of negative pinion angle.
- If the rearend is so close to
level that you can't tell if its nose up or nose
down, put the angle finder on the yoke and then see
which direction you have to rotate the finder to
make it read zero (or 90 depending on how the angle
finder is made). When viewed from the passenger
side, if you have to rotate it counterclockwise, the
rearend is nose down.
- Now that you know the pinion
angle, you may have to change it. On a leaf spring
car, this is done with wedges between the rearend
and the springs. Speed shops and sometimes alignment
shops keep these around. If you can't find them
locally,
QuickPerformance carrys
them. If you have a factory 4-link car, you'll need
some adjustable control arms or revised control arm
mounts. Aftermarket ladder bar and 4-link cars are
adjusted via the Heim joints.
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