 |
How nut torquing and back-off
are used to set wheel bearings
How do we adjust wheel bearings to meet the correct end-play
specifications? Following is a simple, five-step procedure:
1. Torque the adjusting nut to 200 lbf-ft
to seat the bearing components. Always rotate or oscillate the wheel
whiletorquing the adjusting nut to ensure that the rollers are fully
seated against the cone large rib.
2. Back off the adjusting nut one
full turn or until it’s loose.
3. This is where you actually
establish end play. Torque the adjusting nut to 50 lbf-ft while
rotating the wheel hub assembly.
4. Back off the inner (adjusting)
nut the appropriate amount as indicated by the chart at right; e.g.,
1/6 of a turn for a 12-threads-per-inch front steer axle. See chart
at right for the exact back-off amount.
| WARNING:
Failure to back off the inner nut as described may cause the
bearing to run hot and be damaged. If this happens
during operation, the wheel also may lock or come off, causing
a risk of serious bodily harm. |
5. On a single-nut system, install a
cotter pin. On a double-nut system install a jam nut and torque it
to the proper specification, which varies depending on the size of
the nut.
Generally, jam nuts less than 2-5/8" should be torqued to
200-300 lbf-ft; nuts 2-5/8" and over should be torqued to
250-400 lbf-ft. See chart for exact torque specification.
The final step is to use a dial indicator to verify the end play or
free movement of the tire and wheel assembly along the spindle axis.
We will discuss dial indicators in Part 7 of this series on bearing
adjustment.
| Adjusting
Nut Back Off |
Jam
Nut Torque |
| Axle Type |
Threads
Per Inch |
Final
Back Off |
Nut Size |
Torque Specifications |
Steer
(Front)
Non-Drive |
12 |
1/6 Turn |
Install
Cotter Pin to Lock
Axle Nut in Position |
| 18 |
1/4 Turn |
| 14 |
1/2
Turn |
Less
Than
2-5/8"
(66.7 mm) |
200-300
lbf-ft
(271-407
N-m) |
| 18 |
| Drive |
12 |
1/4
Turn |
Dowel Type
Washer |
300-400
lbf-ft
(407-542
N-m) |
| 16 |
Tang Type
Washer |
200-275
lbf-ft
(271-373
N-m) |
| Trailer |
12 |
1/4
Turn |
2-5/8"
(66.7 mm
and over) |
300-400
lbf-ft
(407-542
N-m) |
| 16 |
|
|
