A few weeks ago I posted a question about the length of the drive shaft on my 1970 Plymouth Satellite (318 c.i., 904 TorqueFlight tranny). Many of you recommended I jack up the car in the rear such that the rear axle was under full load, disconnect the drive shaft at the pinion yoke and shove it all the way in to the bottoming out point in the tranny, make a mark on the front yoke at the point where it was all the way in and back it back out to the point where it almost fell out to see how much yoke was actually in the transmission.

I did what you suggested and took the attached pictures. In summary, when sitting on the ground at normal load and jacked up where the rear axle is under the load, there is about 2" of front yoke showing between the bottom out point and the back of the transmission. I pulled the drive shaft out all the way to the point where trans fluid started to leak (should have been about a 1/16" or an 1/8" still left in the tranny at that point) and pushed it back in just enough to stop the leak (about another 1/8"). So, at that point, I have about 3/16" of an inch in the tranny. I measured from the back of the tranny to to the mark I made on the yoke, which was the "all the way in/bottoming out point" and came up with about 4" (see the pictures..the tape rule was at a bit of an angle and if flat it would have been about 4").

That means there is about 2"+ in the tranny at normal load and 2" showing.

Question: Is that enough or do I need an inch longer drive shaft?

I also did what some of you suggested and that is to shove it all the way in to the bottoming out point, back it out 1" and then measure it. The length would be 56 1/2" (versus what it is now at 55 1/2"). That would put 3 inches in the tranny with 1" play/give to the bottoming out/all the way in point.

Once all that was over, I put everything back together and jacked up the card ON THE FRAME this time to let the rear axle drop to see how much of the front yoke came back out. I couldn't get the car completely to the point where the back wheels were hanging off of the ground, but did get it to drop about 3 1/2" (see pictures) and there was no movement backward on the drive shaft.

Bottom line, right now I have a 55 1/2" drive shaft (which I think is standard) that leaves 2"+ in the tranny at the front yoke. Do I need to get an inch longer drive shaft? I don't have any vibration, no trans fluid leakage driving under normal highway conditions. I would like to run it down a drag strip just for fun (knowing it won't be that fast...just to participate...like at the Mopart Nats) and wondered if I'm OK as is or need the new shaft?

Thanks! Chris.

Well, I've added pictures before, but for some reason (its a Monday, ugh) I can't seem to find the link to add the pictures (argh), but hopefully, my description is detailed enough. Let me know. Thanks for your advice. Chris.

The drive shaft only moves in and out about a 1/4" in use. As long as it has enough in it when at full droop and it does not bottom out at full compression you should be good.

The pic below shows the u-joint position with the suspension loaded, in the case of the 904 you want 3 5/8" from the rear of the tailhousing to the center of the u-joint.

SuperCuda and John: Thanks for the reply! John: Your graphic is good, that's almost exactly what I have as a measurement from the back of the tranny to the center of the yoke, but wouldn't another factor be the length of the yoke? Sounds like the drive shaft is right on. The question would be, "What is the standard front yoke length for my car?" Anybody have any idea? Thanks again. I could not have completed this build that took 7 years without all of your chiming in. I'm not just blowing smoke. I really mean it. I do appreciate the feedback! Chris.

Oh...and what happened to the link to upload pictures? I read in the FAQs that one can only upload from a website now. Is that correct? Thanks!