Re: Torque spec????

Posted by DavidPackard On 2022/6/26 18:01:01

Chris, as others have said, prior to the early ‘50s the torque specification for the rear axle nut was ‘tighten securely’ . . . while the later guidance was 200 – 270 ftlbs for both the 3/4 inch and 7/8 inch thread geometries. I checked the recommend torque for a 3/4 inch fine thread bolt and found, 223 ftlbs for Grade 5, and 315 ftlbs for Grade 8, so the Packard torque recommendation is not out of line . . . given that the OEM was not constrained to just two particular heat treatments.

The plot thickens . . . most of us subscribe to the notion of a completely dry taper, but don’t mention thread lubricant, or the contact surface between the nut and washer. During production I believe the assembly was dry in all locations, but all surfaces, especially the surface between the nut and washer were ‘new’, that is free of any gouging from previous use. I renewed the washers with Grade 8 hardware, and ‘dressed’ the nut face with an oil stone before the first attempt to have a castellation align with the torque ‘in range’ I was lucky that I could install the cotter pin with the torque in range. After about 100-200 miles I re-checked and found that the torque was below the minimum, and the nut needed a bit more ‘dressing’ to achieve the torque ‘in-range’ and pin aligned. A loss of torque on a tapered hub is not uncommon during initial run-in. Tightening of the axle nuts can be done with the weight of the car on the wheels . . . emergency brake off. I prefer to back-off the service brake adjustment a bit, and then do the final adjustment of the rear brake after the axle nuts have been dealt with.

A 7 year old grandchild on the end of a four foot bar should be close to the correct torque.