driveshaft question with a teaser pic

[pashtrd]

I am almost done with the motor install on my 69 Torino. Adding a scattershield in front of the trans made my driveshaft too short. It was already too short to begin with, now I cant even get it to fit.
A buddy of mine had a shaft laying around out of some kind of mopar. I installed my slip yoke on it, added the right U joints to make it work. I have 2.25" of engagement into the tailshaft of the trans....Is that enough?
http://i79.photobucket.com/albums/j128/pashtrd/4-26-09-06.jpg

[wrath]

For a slip yoke then you need no less than 1.5x the spline diameter assuming you have a good tailshaft support bushing.

I'd run it, but that's me.

Since you don't know the source of the shaft, are you sure it can support what you're planning on doing with it?

[pashtrd]

I have no idea if it can support what I am planning on doing. But right now I cant afford a new shaft. This will have to do for now. There is no way the stock shaft should have lived behind my old motor, But it handled 4500 rpm launches with slicks. I guess for now that is a chance I am willing to take. I have a loop in case something lets loose.

[Russ Jerome]

The other concern would be a high speed vibration due
to the un-used section of the slip yoke hanging outboard
of the actual output spud. Broomhandle theory.

With everything balanced and driveline angles correct
it may be a non issue and work just fine. The 150%
engagment rule as noted before works on high power
jeeps even with there horrible driveline angles.

[pashtrd]

Well, anytime I have ever had a new shaft built the shop had me push the slip yoke in all the way and back it out about an inch, measure from there. Right now the shaft is sticking out 2". I think I will be ok?

[juicedimpss]

ideally,the yoke should be about 3/4 of an inch from bottoming out at ride height.

[Russ Jerome]

Are you leaf sprung?

With the apearance of your old launch Im guessing the
rear end is planting good right? Correct anti squat wont
make the rear rise too far (pulling the shaft out further).

Regardless of squat or anti squat a leaf sprung car is
gonna have its rear axle move back away from the trans
just a hair more assuming it is shackeled in the rear of
the rear spring. If it has some ladder setup it may give
you another hair of safety. An obvious concern would also
be in braking, a soft rear shocked drag car is gonna have
the rear end lift as you try and stop that monster at the
end of the 1320'.

Im with Wrath, get her running and driving, start slow
and maybe pull the shaft after some solid launchs and
look for gauling.

[pashtrd]

Rear is leaf sprung with homemade traction bars. They work very well. I have Heim joints at both ends of the bar. They attach the rear axle to the subframe.I dont think they will allow any forward / aft movement. but they might.

[07ROUSHSTG3]

more pics please!

[pashtrd]

http://i79.photobucket.com/albums/j128/pashtrd/393-2.jpg
http://i79.photobucket.com/albums/j128/pashtrd/4-27-09001.jpg
http://i79.photobucket.com/albums/j128/pashtrd/5-01-09001.jpg
http://i79.photobucket.com/albums/j128/pashtrd/5-01-09002.jpg
last but not least...my 2 little helpers
http://i79.photobucket.com/albums/j128/pashtrd/4-27-09002.jpg

[wrath]

You need at least 1/2" more room left in your slip yoke than the closest you'll ever get.

And depending on setup, the closest that rear pinion gets might not be at full suspension compression. It might be with the suspension drooped with the pinion pointed up (heavy throttle over a bump, or my favorite: wheelhop).

With leaf springs I usually measure by pretending the leaf is flat (easy to do with a piece of 3/8" cold rolled) and the shackle laying as close to flat as possible. Then I measure from the axletube centerline directly to the output shaft on the transmission. You can then subtraction from this length the distance from the axletube centerline to the pinion yoke centerline and then the slip yoke. At the other extreme I measure pretending the leaf spring is at full droop and do the same thing (pretend the pinion is pointed directly at the slip yoke).

I've seen a lot of carnage from too short or too long driveshafts. I've been lucky, the only time I had a problem was when I was climbing up the side of an 86 DeVille my front shaft fell apart.



You already have the parts you need it sounds like. So unless you're going to try to overbuild a driveshaft I'd just save up some dollars and retube one you've got. But, I'd probably just run the one you've got.