GMC 1986 P-Truck Service Manual page 412

4C-2 FRONT AXLE
The front axle is a hypoid gear axle unit equipped
with steering knuckles and an automatic or manual
locking hub. The K10 and 20 models use a Chevrolet
front axle having an / -inch ring gear axle rated at
8 1 2
3600 pounds for the K-10 and 3800 pounds for the K-
20. A Dana (60 Series) axle is used on the K-30 model
DIAGNOSIS OF THE FRONT AXLE
ROAD TEST
• Check tires for irregular wear.
• Check tire pressure.
• Check axle lubricant level.
• Drive to warm up the front axle.
• Test at various speeds in drive, float, coast and
while cornering.
• Verify that the hubs are locked.
TIRE NOISES
• Change the tire pressure to minimize noises.
• Drive over different road surfaces.
• Smooth black-top minimizes tire noise.
• Cross switch the tires, if necessary.
• Snow tire treads and studs cause added noises.
ENGINE OR EXHAUST NOISES
• Drive slightly above the speed where the noise
occurs, place transmission in neutral.
• Let the engine speed drop to idle.
• Stop the vehicle.
• Run the engine at various speeds.
TEST FOR WHEEL BEARING NOISE
• Drive the vehicle at low speed on a smooth road.
• Turn the vehicle to develop left and right motions,
traffic permitting.
DESCRIPTION
and is rated at 4500 pound capacity. The Dana axle
has a /
9 3 4
on all models to engage the hub whenever four-wheel
drive is selected. A manual locking hub is used on the
K-30 model only and must be engaged manually when­
ever four-wheel drive is selected.
• Noise should change due to cornering loads.
• Jack-up wheels to verify roughness at the wheels.
*TEST FOR DIFFERENTIAL
• Drive the vehicle at low speed on a smooth road.
• Constant low pitch bearing noise may be heard.
• Noise should not change in reversing turns.
• The noise pattern should vary with the wheel
speed.
*TEST FOR PINION BEARING
• Rough running or a whine noise should increase
with speed.
• Noise pitch should be higher than differential
noise.
• Perform the test on a smooth road to minimize
tire noises.
• Perform test at various speeds in drive, float, and
coast.
• Rear pinion bearing noise may be louder on
acceleration.
• Front pinion bearing noise may be louder on
deceleration.
• Gear noise tends to peak in a narrow speed
range.
' Bearing tests should be done in 2H (after 4H
selection to lock hubs). This removes the transfer case
whine.
-inch ring gear. Automatic hub locks are used
BEARING NOISE
NOISE