How to determine proper Driveshaft length?

I looked at the diagram on Denny's driveshaft page, but I have some questions. I am trying to find out what length my driveshaft needed will be. I have a 3.5" aluminum DS already, and I have measured the #6 overall length to be 45.5 inches. I am trying to see if my DS is the correct length or not, how to go about in doing so. The total length of my DS now is 47.5 that is from the back of the U-joint all the way to the end of the slip yoke on the other end. Can someone shed some light on this for me?

You need ~1.25" of splines exposed at the slip yoke.

Rich

You need ~1.25" of splines exposed at the slip yoke.

Rich

By this statement you mean, once the DS is installed and tightened up, that there is 1.25" of splined slip yoke left for travel in and out when the suspension/rear goes up and down?

I guess you are following the directions on their site.
http://www.dennysdriveshaft.com/html/how_to_measure.html
What diagram did you use? B, right? That is the recomended one for us...
http://www.dennysdriveshaft.com/html/b.html

There are many guys that run like Rich with ~ 1 1/4" travel, but denny's recomends between 3/4 - 1"
http://www.dennysdriveshaft.com/html/faq.html#How much slip travel should I have

Yeah, I was thinking of a drag car. 1" or or even 3/4" is proably ok for a street car.

Rich

Yeah, I was thinking of a drag car. 1" or or even 3/4" is proably ok for a street car.

Rich

Well, I have 1 3/8"...is that too much than?

Anybody have an opinion on this...?

Yes this is probably too much, maybe if it was a race only car that had a lot off susspention slack and running 33" tires at almost no pressure then maybe. But for even the most extreme stock style suspension f-boddies should need more then 1 1/4. Are you getting any vibe?the problem with it out that far is it will kill the bearings in the output shaft because it is sitting further back meaning the U jouint and everything is further back. It would be just like this (http://www.dennysdriveshaft.com/html/faq.html#My driveshaft is too short. Can I put on a longer slip yoke to make it fit better)

Yes this is probably too much, maybe if it was a race only car that had a lot off susspention slack and running 33" tires at almost no pressure then maybe. But for even the most extreme stock style suspension f-boddies should need more then 1 1/4. Are you getting any vibe?the problem with it out that far is it will kill the bearings in the output shaft because it is sitting further back meaning the U jouint and everything is further back. It would be just like this (http://www.dennysdriveshaft.com/html/faq.html#My driveshaft is too short. Can I put on a longer slip yoke to make it fit better)

Thank you very much. I will re-measure because i am a bit hasty when I measure, and rather than take my time I rush a guess rather than be exact. I will re-measure and if I was correct i will get a new shaft.