4.9.1 Driveline Balancing
An unbalanced driveline causes transverse vibrations or bending movements in a
driveshaft. This type of vibration is directly related to driveshaft rpm and usually is most
noticeable at a specific driveshaft speed. The cause is imbalance in the driveshaft and,
without using specialized equipment, it can be difficult to pinpoint.
Attempting to balance a driveshaft without spinning it up is so much of a hit-and-miss
process that it is unrealistic to attempt it. We will outline here a simple method of
dynamically balancing a driveshaft assembly using a balance sensor and strobe light.
4.9.1.1 Dynamic balancing
You need a balance sensor and strobe light, preferably from a kit designed to
dynamically balance driveshafts. You will need to raise the truck off the ground and
place it on stands ensuring the following:
1. Frame is level.
2. Transmission and differential carrier housing(s) angles are the same when raised
as when on the ground.
3. Chassis is secure enough on the stands that the engine safely drives the
drivetrain to normal road speeds.
Fit the balance sensor to the chassis to be
tested. The test procedure is similar to that
used when balancing tire and wheel
assemblies. Using the strobe light and white
machinist's crayon, mark the driveshaft and
spin it up. If it is out of balance on this initial
test, begin by removing any counterweights
tacked onto the driveshaft with a cold chisel.
Remove any weld by lightly grinding with an
angle grinder.
Run the vehicle at those equivalent road
speeds noted on the road test when the
vibration was most noticeable. Use hose
clamps to clamp counter weights (steel
washers or blockweights) into position with
the clamp worm screw located over the
weight washer (
Figurer 8-55
). When the
imbalance has been neutralized, tack weld
the weight or weights into position. The
Figure 8-55 -
Balancing a
propeller shaft.
weight of the weld tacks should be approximately equivalent to that of the hose clamp
worm, so make a practice of always locating the worm over the balance weight.
CAUTION
Use small tack welds to attach weights. Larger welds can create another imbalance or,
worse, distort driveshaft tubing.
NAVEDTRA 14050A
8-63