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This page contains a reference chart of torque values for tightening u-bolt nuts on vehicle axles. It assumes a light coating of machine oil on the threads has been applied. The figures represent ultimate torque values for the size thread indicated. Actual torque applied to u-bolt nuts is also dependent on the ability of the anchor plate to take the pressure without deforming. A lot depends on proper tightening as the leg of the u-bolt must be stretched to do its job, but as in many mechanical systems final judgement falls to the technician and his knowledge. An example would be of a Pickup Truck Rear Suspension using 5/8" diameter u-bolts passing through a 1/4" thick anchor plate (a plate which will deform with much less torque applied than near the ultimate figure on the chart). This situation requires a lesser torque than the published values. However, a three ton dump truck using 7/8" diameter u-bolts anchored with a heavy iron plate will require full recommended torque, and be retightened after a few hours service. Since this chart gives ultimate values of torque, our shop has found ninety percent of the figures to be sufficient for final torque on a given size u-bolt. For example: 1800Lb/ft torque is recommended for 1-1/4" Grade 8 equivalent u-bolts; 1890Lb/ft would be ninety percent of the maximum allowable figure of 2100Lb/ft. |
| Bolt Size and Thread | Grade | Max.Torque (FtLbs) |
|---|---|---|
| 1/2 - 20 | 5 | 92 |
| 9/16 - 18 | 5 | 131 |
| 5/8 - 18 | 8 | 256 |
| 3/4 - 16 | 8 | 446 |
| 7/8 - 14 | 8 | 710 |
| 1 - 14 | 8 | 1057 |
| 1-1/8 - 12 | 8 | 1522 |
| 1-1/4 - 12 | 8 | 2107 |