9-inch is a 9-inch is a 9-inch, right? Well, not really. I think it's safe to say most of us would answer the opposite given obvious things like the addition of a posi or a locker-type gear. Yeah, there's the difference in housing shapes throughout the years and the number of splines on the axles, which come in either 28 or 31 splines from Ford, that have transferred power to many a rear skin all these years, but besides the three-spline difference, what else is there, and why is it surprising to find out that '57-64 rearends aren't what we've been led to believe?

It all started out as we tried to install a Master Power rear disc brake kit on a '60 Ford F-100, with its presumably stock 9-inch rearend. The first thing we noticed that would send us down the road of education was that the distance from the face of the axle where the brake drum mounts to the face of the axle flange on the housing was too narrow to get the new caliper set up into...hmm. Well, who else to call for 9-inch help? Currie Enterprises in Anaheim, California, the 9-inch gurus, of course!

In the first of what would be many conversations with Ray Currie and Brian Shepard, we found out we were up a creek as far as installing the disc brake kit on the '60 was concerned, because the pre-'64 9-inches are 1/4 inch narrower than the later versions. Now what? Ray answered that question real quick. These early white-iron third members are only good up to 265 horsepower in a full-size car or truck, and many are unknowingly cracked around the rear pinion support bearing under normal duty thanks to the inferior iron used to cast them, which gives way under pinion deflection. The F-100 that's home to the rearend in question will be the recipient of a 392 Ford stroker from Smeding that will easily surpass the stock early rearend's threshold and will still need those Master Power discs out back to slow the train down. It was obvious even at this point that a new rearend was needed.

Keep reading for a quick pictorial lesson from Currie on what makes a 9-inch a 9-inch and how we got the disc brakes from Master Power hung on one.