Drive shafts, double cardan or not?
 

When I got my 79 F350, the truck was jacked up 6 inches, but the front drive shaft was, I thought OEM stock equipment. I just had another made a couple days ago and now I hear the original front drive shaft was double cardan, is this true? The original owner also had the slip yoke end at the transferase, but I hear its to be at the drive shaft. Who has had their trucks jacked up 6 inches and should this be a double cardan joint and were they that way from the factory?
Any info on this would be great, since I have not put the drive shaft on the truck and can have it sent back to have it modified to a double cardan before doing so.
Thanks!!

Could be single (upper pic) or double (lower pic) cardan.


https://cimg4.ibsrv.net/gimg/www.for...bd2bc73e32.jpg


https://cimg7.ibsrv.net/gimg/www.for...ff1fae4bd3.jpg

What's the application difference? Is it dependent on transmission /tcase/axle option? Full time VS part time 4wd? Or are they interchangeable?

Interesting, so they came both ways and according to the photo, the slip yoke is at the transfer case. Now Im confused, since everyone who I have asked so far on forums, have said, slip yoke at axel. So now things are as clear as mud. :)

When a double cardan (or more commonly referred to as a constant velocity joint) is used the slip shaft always mounts at the axle end.
https://cimg1.ibsrv.net/gimg/www.for...9a436751f.jpeg
my '79 F350 with T-18 4 spd & np205 part time T.C. setting on 6" suspension lift with the double cardan D-shaft.
For what its worth, I've been under many 77-79F250 4x4's & the 79F350 4x4's & I've never seen a truck equipped with the single cardan D-shaft.

Thanks for getting back to me and great info. That said, what a bummer, just having this thing done and now having to get it done again. At least it will be done right. Thanks again!!

your welcome! You also need to be aware that the T.C. yokes(or companion flanges as Ford called them) are different between the single/double cardan D-shafts & NumberDummy's post reflects this info too.

If you do go with the double cardan setup, install the double cardan companion flange at the T.C. first, because it will effect the final measurement of the D-shaft length.
reference pic of double cardan D-shaft & mounting hardware.
https://cimg7.ibsrv.net/gimg/www.for...acaf20aaa7.jpg

Thanks Chris, I contacted the drive shaft shop and my New drive shaft can't be modified for a double cardan. So Im going to use it just the way it is for now to see if there is any vibration. Thing is, mine is set up with single cardan in mind, reflecting on your post knowing the flange would also need to be changed. Since mine is a single, your previous post made mention that the double had the slip yoke at the axel, are you saying "to be clear" that the single cardan, yoke end would connect to the transfer case? If I do that, the grease nipple will hit the crossmember. I will need to grease the slip yoke off the truck and then plug it, before install to clear the cross member. The cross member that is in it has been dropped 3/4 of an inch already, but not enough for the grease nipple to clear.
Your thoughts on orientation of a single cardan in my case?

The single cardan D-shaft with only 2 u-joints can be mounted in either position as long as there is enough clearance to do so...suspension travel needs to be accounted for as well, when checking clearances.

I think the idea behind mounting the single cardan slip-yokes at the T.C. was to keep them up in the chassis, away from debris/hazards, possibly extending the life of the parts involved. With a double cardan style D-shaft, this is not possible. The double cardan end needs to be mounted in a fixed position at the T.C. to prevent it from binding, as opposed to the axle end which moves up/down as the suspension cycles.
Honestly, if you have clearance issues like you've described, I don't see the truck being functional for any type of offroad use...if that's your intentions. An example would be...dropping the left front tire into a ditch and the other 3 tires are still on level ground, this would result in contact between the D-shaft & the crossmember as the suspension "droops" down following the contour of the ground.

Driveline angle need to be considered too! A single cardan D-shaft has a certain range of acceptable angular motion & once you get outside of that range you'll experience excessive vibration & increased u-joint wear. The beauty of the double cardan style D-shaft utilizing 3 u-joints, is that it effectively cuts the driveline angle in half allowing a much steeper angle between the axle & T.C. ,eliminating vibration & wear that would be present with the single cardan style. Your driveline shop, if reputable, should be able to explain this much better than I can.

Not knowing how your front suspension is setup, you may need to shim the front axle, rotating the axle pinion angle up towards the T.C. to get to that acceptable range of angular motion. Do keep in mind that shimming the front axle also changes the axles castor angle...if you go too far here you'll start to experience ill-handling characteristics. Castor angle effects the truck's steering ability to return center when coming out of a turn. I use 2° shims on my setup & don't experience any ill effects.
Modifications to the crossmember may be required to get sufficient clearance as well.

There's an awful lot to consider when setting up a functional 4wd system! Hope this was helpful.

Thanks Chris! great since I am new to 4x4. When I described what I intend with the truck to the drive shaft shop, they said I will be fine with what I have. Im not going to be off roading, bud bogging with this truck like some would. That said, the occasional light fun will be in mind. Once the truck is finished, It will be dropped a couple inches, to a 4 inch lift and a nice black paint job and trim. Im not going to want to damage the thing after, but the idea of having a truck I can pull with, load to the rafters and get though some bad weather with, is what it will be used for mostly. I will be putting it on the road shortly, but it will only see snow I hope! a couple times if need. Im defiantly going to keep my eyes open for a double cardan shaft in the future, but now that this new single has been made and can't be changed to a double, It's here to stay for now.

With a 6" lift, even a 4" lift you most likely would want a double cardan joint. The double cardan joint will cut your U-joint angle in half and usually since the engine/transmission assembly is sloped rearward, and the distance from the front transfer case output shaft and front axle yoke is so short, the angles are very steep. It might be "ok" if there is no binding and you are using it at very low speeds, but anything more than that definitely want to consider a double cardan joint at the transfer case.

I've only ever seen one 77.5-79 F-250, that I knew for sure came from the factory without a cv.

I defiantly will be getting one then, knowing before would have saved a lot of money, but thankful for all who responded with info. This site has a lot of people willing to help and that makes for a great site, Thanks!!