The 510 Realm

Question. I'm getting ready to mount my driveshaft. 1970 Datsun 510 (obviously). S14sr20det with 5 speed. Is there any magic formula for determining how much I need to have it shortened? I.e. Distance from tip of trasmission output shaft to surface of differential input flange. I've slid the transmission end of the shaft onto the output shaft but because it's too long I can't accurately make a mark on the driveshaft where the driveshaft flange would be when shortened. I can guesstimate it allowing for a bit of play the driveshaft should have to slide on the output shaft for drivetrain movement but if there is a known method that would be great to know. I only want to have the driveshaft length done once, know what I mean? Any help is of course much appreciated!

Talk to a shop that specializes in drive shaft shortening not just a garage. I don't know but would guess from the center line of the rear U joint to the outer case of the transmission. They will know how much to move the front U joint back so you have a proper amount of spline engagement yet have some slip for engine and differential movement when accelerating and decelerating.

The driveshaft will be shortened and balanced at a reputable driveline specialty place here. Just have to get the length figured out. Think I'm on the right track now

Different shops like different measurements. Call your shop and ask how they want the measurement taken.

I've always done 36 1/2" center of u-joint to center of u-joint with all KA-SR-CA swaps with an R160 or R180 diff. Could always go 36" if you are worried it might be to long.

That's what I came up with too