WARNING
If grease is seen to exit only from three of the four trunnion seals, the bearing is not
properly lubed and will almost certainly fail. You must take appropriate corrective action
when U-joints fail to take grease. If a driveshaft separates because of a U-joint failure, it
can take out air tanks and fuel tanks, and can generally cause damage that greatly
exceeds the cost of replacing a single U-joint.
2. If grease does not exit from a U-joint trunnion seal, try forcing the driveshaft from
side to side when applying gun pressure. This allows greater clearance on the
thrust end of the bearing assembly that is not purging. If the U-joint has two
grease fittings, try greasing from the opposite fitting. If this does not work,
proceed to the next step
3. Back off the bearing cap bolts on the trunnion that is not taking grease and pop
the cap out about Y inch. Apply grease. This usually will cure the problem, but if
it does not, you should remove the U-joint to investigate the cause.
4. After working the U-joint that fails to take grease, make sure you torque the
bearing cap bolts to the OEM specification.
CAUTION
Half-round end yoke self-locking retaining bolts should not be reused more than five
times. If in doubt as to how many times the bearing bolts have been removed, replace
with new bolts.
4.3.3 Slip Splines
The chassis lubricant used for U-joints is satisfactory for use on slip splines. An EP
grease meeting NLGI grade 1 or 2 specifications is required. Slip spines should be
lubed on the same service schedule as U-joint intervals.
1. Apply grease to the zerk fitting until lubricant appears at the relief hole at the slip
yoke end of the slip spline assembly.
2. Seal the pressure relief hole with a finger and continue to apply grease until it
starts to exit at the slip yoke seal. Sometimes it is easier to purge the slip yoke by
removing the dust cap and reinstalling it after grease appears.
CAUTION
In cold temperatures, you should drive the vehicle immediately after lubricating the
driveshafts. This activates the slip spline assembly and removes excessive lubricant.
Excess lubricant in slip splines can freeze in cold weather to a wax consistency and
force the breather plug out. This would expose the slip joint to contaminants and
eventually result in wear and seizure.
4.3.4 Lubricating Hanger Bearings
Hanger bearings are usually lubed for life by the manufacturer and are not serviceable.
However, when replacing a support bearing assembly, fill the entire cavity around the
bearing with chassis grease to shield the bearing from water, salt, and other
contaminants. You should put enough grease to fill the cavity to the edge of the slinger
around the bearing.
NAVEDTRA 14050A
8-56