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Axle Shaft Taper


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Over the weekend I was helping a friend work on his new toy, a 40 Hupp Skylark, to reassemble the rear brakes. We got one side done easily and well but the other side was trouble. The drum just would not go far enough on the axle shaft to fully seat. It would stop so there was about 1/4" air space between the edge of the drum and the backing plate. Found some burrs and damage at the outer edge of the hub hole in the drum from someone pounding on it trying to seat it I guess. We filed that out but no change in the fit. So we got out the verniers and the hole in the hub at the outer face was .048" diameter smaller than the OD where the shaft taper starts at the end of the threads. I suggested if worse came to worse as a possible remedy he could bore the hub out to the shaft OD so the rear edge of the drum would be flush to the inner face of the backing plate like the other side. This would probably leave the last 1/4" or so of the hub hole without taper but at least it would go on.

A discussion ensued and of course the better fix is to turn the hub bore with the taper and match the tapered shaft size. But that is a lot harder to do for the average guy and much more expensive for a machine shop to do. One question did come up and no one had an answer-

Are all shafts tapered the same like an SAE standard? Or did the taper change from shaft supplier to supplier or automaker to maker? I know all shafts appear to be close but I do not even know the taper spec- 3 degrees? five? 7?

Thanks in advance,

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Yes, these are the drums that came with the car, they appear to be the same rear to rear, and are as received other than turning them. We did switch them side to side and the bad drum fit neither side, the good drum fit both sides properly. That is what got me to checking diameters and finding the one undersize.

I talked to an experienced machinist friend today who explained they are probably a standard Morse taper. Machine shops building large machines would have standard reamers to clean this up and that Hollander's Interchange showed the Hupp as a standalone axle shaft, no interchange available. The owner now has another drum coming from another source so I encouraged him to clean this up and shelve this drum as a spare.


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