Re: Runout of Axle shafts on 1947 Custom Super

Posted by DavidPackard on 2017/8/7 17:02:06
Taking a radial runout of the end of the axle can be problematic. The axle has a bearing clearance that may be in play. The only way to make sure the axle on your side is riding hard on the outer race is to have a helper push the other wheel toward the center of the car while they rotate the wheel. However as soon as they push on the wheel to bring the bearing clearance to zero the whole car is likely to move toward you, so the dial indicator must be mounted to the car . . . not the ground.

With the assistance of your helper you can estimate the amount of force they will need to apply while you are conducting the radial run-out check. Set-up your dial indicator to measure the axial motion of the axle . . . we will actually be measuring the bearing clearance during the next few steps. Start-off with you pushing your axle toward the center of the car. The helper will now pull on their side (both you and the helper are applying force in the same direction). While they're still pulling their wheel outward you pull your axle toward you noting the distance the axle moves. With the helper still pulling on their wheel repeat the axial motion measurement a few times with you moving your axle in and out. Now with your axle pushed in have the helper to lightly push their wheel toward the center of the car. As soon as the full amount of axial motion has occurred your helper should note the amount of force it took to push your axle toward you.

Set-up for the radial measurement and have your helper 'push and turn' with at least the same amount of force as above. While the radial run-out is an interesting measurement I'm not sure that number matters . . . unless it's wildly high. It is the run-out of the axle and hub as an assembly that would matter . . . that is the assembly after the axle nut is torqued to the specified value . . . which is not a trivial amount. If the axle has a small 'tweak' and is asked to slide into the bore of the hub which is true my bet is the hub will help straighten the axle.

The axle/hub interface is assembled dry. Do not hit the hub or brake drum trying to do a better job in seating the assembly. You can tap on the hub radially to help the sliding motion, but not with a lot of impact force. Use a slow and steady torque . . . no impact tools. Most of my friends that have cars with tapered axles advocate a re-tightening of the axle nut after a 100 miles or so . . . I also recommend this re-torqueing practice.

Let's get back to the axial measurement . . . that's the bearing clearance that may be compared to the specified tolerance. If it's OK you can disassemble and repack the bearings knowing that activity will not change the clearance. If the clearance is not correct you will need to adjust the shim stack between the brake backing plate and the rear axle housing. Not a big deal, the written procedure in the shop manual will cover those steps. You want about an equal amount of shims on both sides, so you can check that when you're repacking the bearings. Less shim thickness decreases the bearing clearance; more shim thickness increases the bearing clearance. Replacement of the bearing or axle will require a bearing clearance confirmation.

I've also heard that a collision, or sliding into a curb can 'tweak' a wheel and perhaps the hub. Excessive wheel or hub run out could be a result from a 'wild ride on an icy road'.


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