At Currie, we speak with customers every day about how to measure a 9-inch rearend to order replacement or custom axles. Getting it right comes down to going through six easy steps and reading a tape measure to gather the required information.
Step 1 -Measure The Housing For Axle Length
When measuring a 9-inch housing for axles, Currie prefers to use "X" and "Y" dimensions shown below to establish axle length, as it has proven to be the least error-prone method.
To determine the "X" (Drivers side axle) and/or the "Y" (Passengers side axle) dimensions hook a tape measure on the stud (as shown) and measure to the outside edge of the housing end flange.
Step 2 – Determine The Housing End Type
During its 29-year production run, the 9-inch rearend came with three different housing end types and corresponding axle bearing sizes, with each requiring a unique axle core. The best method for determining the axle bearing size is to measure the bolt pattern spacing of the housing end. With the brake drum or rotor removed, measure the distance between the bolt-hole centers, as shown in the images below.
Step 3 - Axle Brake Space/Offset
Brake space or offset is the distance from the face of the housing end to the face of the axle; this is a critical dimension used to determine overall axle length and proper brake fitment. If you have already have brakes verify that they are compatible with the housing end type and brake space listed in the table below.
|Standard Brake Space Dimensions|
|Housing End||Brake Space|
|Late Big Bearing (Torino)||2.5 in.|
|Early Big Bearing||2.36 or 2.02 in.|
|Small Bearing||2.5 .in|
Step 4 - Axle Face And Brake Register Diameters
The Axle Face and Brake Register diameters are essential Axle dimensions. A smaller Axle Face diameter is acceptable, as this does not create a brake fitment issue. If you are retaining the existing brakes, the Register diameter is a critical dimension, as it serves to locate and center the drum or disc brake rotor. Use a dial or digital caliper to measure the register diameter to 1/1000th of an inch accuracy. If you are purchasing new brakes, then you will need to verify the required register diameter and inside rotor hat dimension before ordering axles.
Step 5 – Wheel Bolt Pattern And Access Hole
If you are replacing an existing axle, it is always good practice to verify the wheel bolt pattern before ordering new axles. Odd-number (5-lug) bolt patterns must be measured differently than even number (4, 6, or 8-lug) bolt patterns to achieve the correct dimension. Odd-number bolt patterns should be measured from the outside of one stud to the center of one of the two opposite studs. Even number bolt patterns should be measured from the center of one stud to the center of the stud directly opposite.
Step 6 – Axle Spline Count
The number of splines on the axle must match the spline count of the differential you have or will be using. There are two ways to determine the required number of axle splines. You can try to count the splines carefully, or you can use a tape measure or caliper to measure the diameter of the axle at the splines. The chart below converts axle diameter to spline count.
|Spline Count||Axle Diameter||Application|
|28-Spline||1.20 in.||OEM 9-Inch Axle|
|31-Spline||1.33 in.||OEM 9-Inch Axle|
|35-Spline||1.50 in.||Performance Aftermarket|