Technical Writer for Internet & Print Media
- Jan 10, 2001
- CenCoast CA
- 71 04 12 19
Just for the record, the original '63 design used slip fits for both the inner and outer bearings, and the drive flange nut was torqued to 50 ft-lbs.
As a result of a spindle failure at the Proving Grounds (which resulted in the wheel, brake drum, and part of the spindle coming off the car), the design was changed, and went into effect at Chevrolet-Warren between November 2 - November 19, 1962. The spindle was revised to provide a press fit for the inner race of the outer bearing, and a chamfer was added at the shoulder of the bearing seat area of the spindle to provide for tool (bearing separator) access.
The diameter at the inboard end of the spindle was revised to provide a .0005" loose to .0005" tight fit for the inner race of the inner bearing, and the thickness of the washer under the spindle nut was increased from .140" to .210"; the drive flange nut torque was increased from 50 to 100 ft-lbs.
The above indicates the change was made as a way to prevent drum brake cars from loosing wheels after an axle breaks, not as a solution to "spun" inner races.
But then, this....
Courtesy of JohnH, Mike McKown and Mike Hanson, here are pages 1 and 2 of the TSB issued by GM on this subject. Note that they do mention the occurrence of the races rotating (spinning) on the spindle which I believe is the primary fault. Mike Hanson further explained the mechanics of why a slip fit inner race can be used successfully on a fixed spindle (like a front wheel) but is not the best strategy in an installation where the spindle rotates. Similarly, this explains why a slip fit outer race would be disastrous for a fixed spindle. Neat stuff.
...indicates the change was made to address "spun" bearings.
Nothing like confusing the issue, eh?
I think I'm going to stick with my slip-fitted bearings and spindle nut torqued to 100 ft/lbs plus whatever additional torque is needed to get the cotter pin hole to line up. It's worked for 20 years...(knock, knock, knock)...so I'll stick with it.
The second post cited above refers to a "Mike Hanson" further explaining the mechanics of slip fits in different applications. Can you post this discussion?
Once again, this has been an interesting exchange of ideas...just what the CAC should do.