1952-59 Ford Is my driveshaft in far enough?

With the Neapco conversion U-joint in, the front yoke on the '85 Crown Vic driveshaft extends 1-7/8" into the AOD tailhousing with the car sitting on the ground. The black vertical line in the pic is right at the rear seal. The AOD tailshaft extends 1-1/4" further into the yoke so a total of 3-1/8" of the yoke is actually engaged. Is that sufficient or do I need a longer yoke?

 

Jack the rear up and stick some jack stands under the frame to let the rear end down to the limit of its travel then mark the slip again. How much spline engagement do you have fully extended? The important part is how much spline engagement you have as the suspension travels. The other important thing would be to make sure the slip doesn’t bottom out against the tail housing when the rear is at its upper limit, the bump stops. Ideally the spline engagement at ride height would be the halfway mark of the upper and lower limit determined by your suspension travel.

 

Look in the "Sticky" there is a link on how to measure for a drive shaft it probably covers that.

 

How far from the open end of the yoke do the splines start?

Looking at the wear on that yoke, from Ford the car that shaft came out of (85 CV?) had ~1" more engagement...

 

One more thing you need to be aware of, is the tail shaft bushing. You will need to have full engagement of the yoke in it.

Bend a small hook on a wire and slide it in. Try to hook the forward edge of the bushing and mark it at the seal, then compare it on the yoke. I wouldn't chance it, unless the there was at least full contact at ride height.

It's much cheaper to shorten a drive line, than lengthen one so, if it has to be longer I would try to find a longer one to shorten.

 

Longer yokes are available from Circle Track suppliers and there are many of them not just the big box stores. I’ve seen 7-9”. I my opinion you need to get up to the witness rust to be safe which would be a 7”.
Splines are not “just specific” to one transmission they fit many; manufacturers are not stupid they engineer to what’s common, cheap, and what’s available. Count the splines and get the OD. If a new u-joint is needed there are combo ones.
A yoke is way cheaper than a lengthening a drive shaft and I’ve done it many times to save $$$$. Good luck.

 

Just a little update.........I tried the hooked wire trick that frnkeore suggested and found the bushing inside the tailshaft housing to be 2" long. My yoke slides in 1-7/8" plus the tailshaft extends down into the yoke an additional 1-1/4", giving me a total of 3-1/8" of engagement. There's also 1-1/4" left on the yoke to slide in further if needed. I'm gonna call that good! Thanks everyone for the help and insight!