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1964 Thunderbird, 390 FE
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Discussion Starter · #1 ·
I was looking at a guy's build thread (not on Hotrodders) this afternoon. He had a 59 Tbird that he was hopping up, and replaced the 3rd member with a posi unit and 31 spline axle shafts. The old ones he took off (I assume factory) were 26 spline, and they were tapered, smaller at the pumpkin end than the hub end. My question is why manufacture these tapered shafts? The 31 splines he put in are basically round stock with the splines cut at the end. Maybe I'm dumb, but would it not be easier to take round stock and just cut splines into it like those 31s are?
 

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While I can't be sure, having been involved in machine work most of my life, it was probably cheaper. The basic axle was forged, so it was most likely very close to the finished size. With 26 splines, there was less machine time required and less material to be removed. Manufacturing in those days wasn't done with highly automated metal removal centers like today that cut metal like it was butter. There were multiple machines required to make that axle with a human controlling each one, although they did have jigs and fixtures to hold the part. The tooling wasn't as good and each reduction in metal removed made the part cheaper and faster to make.

The 26 (are you sure it wasn't 28 splines) spline axle was lighter, too and strong enough to hold up for most use. When stronger parts were needed, Ford was perfectly fine with supplying them, as were most other manufacturers. It just cost more if you were willing to pay for them. Most folks didn't want that extra expense and didn't want to pay it. The car manufacturers were and still are concerned with saving every penny. Just like now, cars were built to a price for maximum profit.
 

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More for Less Racer
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Factory axle spline are not broached, they are rolled into the axle in a machine called a rack roller....the spline is pressed into the axle shaft prior to heat treat.

Aftermarket performance axles are the only axles that are cut splines.

The mating parts to the axle spline, like side gears, pinion yokes, driveshaft slip yokes are broached
 
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