I lowered my F100 5-6" in the rear and changed rear ends from a Ford 9" to a Dana 44.
Now my drive shaft seems to be too long?
This is a 3-speed manual transmission truck.
Any thoughts or advice?

 

Makes sense to me. Call your local driveshaft company to double check me. Or a fellow FTE er will chime in. If I were to measure it I would put slip yoke about 3/4 the way in the tranny and measure the driveshaft center of u-joint cap to center of the opposite u-joint cap.

 

Make your measurement as Jefa suggests. Take the driveshaft you have along with your measurement to a suspension or rear-end shop, have it cut, shortened to the proper dimension, rewelded. Maybe get the u-joints replaced for drill.

Semper Fi

 

Lower the truck and change the diff???

 

Yes, Lizard, I am scratching my head also.
Brother, you have severely distorted the geometry that the Ford engineers put in your driveline. The level of the rear-end goesoutta should match the level at the transmission goesinta. If they do not match, your driveshaft will "skip rope" which means imbalance and the transmission spline slipping in and out to accomodade the mismatch. Even if you cut and fit a new driveshaft you will probably have severe vibrations at highway speeds.
My advice is to get the thing to a rear-end shop, let them adjust the angles of attack on the driveline, cut and reweld the driveshaft.

 

Going with what Jeff advised first.
Not quite ready to relocate the perches just yet, Cougar...
However, if this doesn't work I will try that next!
Thanks!

 

I believe you can get some thin tapered spacers for at the spring pads to change your pinion angle.

 

Yes! That sounds like a super easier way to change the angle!
I know it may have seemed like a crazy idea to change the entire rear-end, but I came across this Dana 44 at a bargain. ($120)
It is super clean and it came out of a '66 F100, plus it already had a posi-unit, and a 3.54 gear, which is two of the upgrades I was looking for, so I just couldn't pass it up!
I am scheduled to pick up the drive shaft no later than Tuesday of next week.
I hope it will work out.
I will keep you updated.
Here's a few pics:

i1353.photobucket.com/albums/q674/BrotherMabe/null_zps03953774.jpg
i1353.photobucket.com/albums/q674/BrotherMabe/390-32_zpsa394bb29.jpg

 

 

I got an adrenaline rush after those two pics there buddy! Phew!

 

I am putting the shortened drive shaft in soon.
I am hoping that the pinion angle is ok.
If not, I did find a machine shop that makes the shims for the perches on the Dana 44.
Im excited about getting everything put back to see how it works.
Ill keep everyone updated...

One more pic here:

 

I lowered my short bed 5-3/4" in the rear. My driveshaft was just a taste too long after the lowering mod. I kept the stock driveshaft and had a brand new driveshaft built in case I want to return my truck to stock height. I always tell people to measure the pinion angle prior to any rear suspension mods. 4-5 degrees upward should be good. The pinion angle should mirror the driveline angle.