Re: Rear axle help (54-55)

Posted by DavidPackard On 2024/6/16 22:00:13

HPH

Pinion bearing adjustment is somewhat similar to adjusting the clearance of the outboard axle bearings, except in the case of the pinion bearings the clearance is considered negative, meaning the bearings are tight enough to produce a rotational drag. Some manufactures used a shimming procedure that was somewhat iterative. I don’t know of any designs that had a threaded adjustment for the pinion bearing adjustment, but given the number of designs there may be at least one that featured an adjustable feature, but alas not the Packard design.

Fast forward to a simpler design of setting pinion bearing preload that does not require a distance measurement, or shimming, and can be done once and once only. This simpler design places a spacer between the bearings. This spacer is a piece of tubing (pinion gear passes through the center) that starts life longer than needed. A long spacer results in loose bearing that would have much less than the required drag torque. One more special feature of this design is the spacer tubing has a bead rolled in it. The bead is proud on the outer diameter. Most shop manuals suggest this bearing spacer is a ‘use once’ item.

As the pinion flange nut is tightened the inner races of both bearings and the spacer become in intimate contact, but may not yet be the correct total length. Addition tightening of the flange nut begins to collapse the tubular spacer and the length is approaching the correct length. The bead in the tubing is the location where all of the plastic deformation is occurring (that’s why the bead is there in the first place) . . . the spacer is getting shorter. You continue this process until the required drag torque is correct. By using a collapsable spacer the pinion bearing drag is an assembly process that is not iterative.

One of my non-Packard shop manuals suggests a torque of 350 ft-lbs may be required to collapse the spacer. The forums advise on pinion seal replacement stress the idea that getting the pinion nut back to the same position with respect to the pinion shaft is a recognition that the collapsable spacer should be returned to the same load / dimension . . . not tighter, or looser. Ultimately, we’re trying to get back to the same bearing preload.

Since you have a bare case you will be determining the correct spacer length by measuring the rotational drag of the bearings and seal. By the way, the bearing drag adjustment is a completely different process from the pinion depth shimming.

dp