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Axles & Axle Bearings

Purpose of the Axle

Rear axle shafts for both sides

The axle has one basic task to perform: transfer the torque from the differential and make it available to the tires. The differential provides gear reduction and controls traction bias which allows one axle to slow down, and the other to speed up, in turns. This is essential because the outer wheel in a turn travels farther than the inner wheel.

Full-Float & Semi-Float Axles

Most axles can be broken down into either Full Float or Semi Float. The main difference between the two: A Semi Float Axle supports the full weight of the vehicle and its load with the axle being supported on a single bearing attached to the end of the axle housing. Full-Float axles have a wheel hub and bearings that are supported by a fixed spindle. This design supports the vehicle weight and its load, leaving the axle only one function, to transfer torque to the wheel.

On a full-float two-piece axle the shaft is splined at both ends with one end plugging into the differential and the other fitting into a drive flange that bolts to the wheel hub. A nut at the flange end prevents end float. The weak point in this design is that there is always some movement in the splines which will lead to wear over time. The two-piece axles were popular in their day because it was difficult to make a shaft with a flange economically.

Older two piece semi-floats axles are similar, but instead of a drive flange, they use a wheel flange. This flange features a tapered socket with a parallel key and secures to the axle with a big nut. In some cases there might also be a set of splines. The disadvantages are the same as the full-float setups above; wear and loose fasteners can take a toll.

Axle Steel Grades

Complete Axle bearing adjuster and seal kit

Axles are typically made with either Carbon steel or Chromium-Molybdenum (Chrome-Moly) steel.

Chrome-Moly Steel (SAE Grade 41xx) is not a given for all high strength axles as it’s more expensive to produce but is considerably stronger than standard Carbon Steel. Carbon Steel (SAE Grade 10xx) is less expensive and easier to weld at home but more prone to breaking.

The xx in the SAE grade is the carbon composition of the steel in hundredths of a percent.

Dissassembling an Axle

Disassemble Open Knuckle Axles

  1. Preliminary Operations: Remove Wheels and hub.
  2. Remove the bolts that secure the spindle to the knuckle.
  3. Remove the spindle

Disassemble C-Clip Axles

  1. Preliminary Operations: Remove the cover, drain the oil, remove the wheels, and remove the brake drums.
  2. On an open diff, remove the pinion shaft retaining bolt.
  3. Remove the pinion shaft (Most times it will simply drop free).
  4. Inspect the pinion shaft for wear, if you find wear then inspect the carrier and differential gears.
  5. Push the Axle shaft in slightly and remove the c-clip.
  6. Remove the axle shaft and inspect the bearing surface and seal surface.
  7. Remove the bearing.

Disassemble Pressed Bearing Flanged Axles

  1. Preliminary Operations: Remove the wheels and brake drums
  2. Unbolt the bearing retainer.
  3. Pull the axle.
  4. The wheel bearing race needs to be pulled from the housing end.
  5. Remove the pressed-on collar, snap ring, or nut that secures the bearing.
  6. Remove the Bearing

Disassemble Full Float Axles

  1. Preliminary Operations: Remove the wheels and brake drums (if separate from the axle hub).
  2. Remove the bolts or nuts that attach the axle to the hub.
  3. Remove the axle shaft
  4. Remove the hub-bearing retaining nuts.
  5. The hub will come free when you remove the final nut.