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How to Measure Driveshaft length for your T56 magnum swaps

One of the most common questions I get is how to measure for your driveshaft.

The way I prefer you to do this is to take the end of the tap, and put it on the face of your rear differential flange, then pull the tape up to the transmission, and take a picture so I can verify the measurement.

You want the total measurement to be from the diff flange face to the base of the seal (or back of the tailcase) on the T56. You are NOT measuring to the tip of the seal, NOT measuring to the back of the output shaft, but to the back of the tailcase where the seal base is held in place.

Take me a picture like this:

measure driveshaft for t56 magnum swap

The seal on the T56's has a "boot" which protudes backwards, this is not where the seal actually resides, so you need to measure from the base of the seal.

For those of you with a flange/flat yoke on your diff, this is what you will be measuring:

measure driveshaft flat yoke

If you have a flat output flange on both your transmission and diff, this is what you are measuring:

If you have a pinion flange that uses u-bolts or straps (like a 9" FORD) then you will be measuring like so:

pinion yoke u-bolt straps
To measure a pinion flange for dimensions, here is how you do that: 

-If you aren't sure what size u-joint you have, measure as the pinion yoke as shown here:

Be very careful and accurate with these measurements as the size changes in increments of 1/16" (1-1/16" | 1-1/8" | 1-3/16").... And let us know if you have locating tabs (as shown) or if your yoke uses an inside clip:


Flat Flange: 

If you have a flat flange, we may need a flange measurement to identify the correct one, see the diagrams below for how to measure 3-Bolt, 4-Bolt and 6-Bolt Flange patterns. NOTE: ANY RUBBER GUIBO COUPLERS MUST BE REMOVED BEFORE MEASURING