How to Identify Your Power Steering Gearbox Input Shaft

One of the calls we get all the time is people trying to identify what kind of input shaft they have on their gearbox.

On Saginaw boxes, there are 2 options:

  • 13/16 36 spline, which was pre-1980
  • 3/4 30 spline, which was after 1980

The problem with this is the spline count is counted as if there were splines all the way around the shaft. But these input shafts always have a flap. So there will be splines missing.

So on a 13/16 36 spline, you'll only have 31 or 32 splines – because of the ones that are missing from the flap. But if you were to measure it, it'll be around 800 thousandths. 800 to 805 is the range these will usually measure at for 13/16.

A 3/4 30 will have about 24 splines and will measure around 720-725 thousandths.

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