Hi folks
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Im more of a reader than a poster, so please excuse my newbie status. However ive run into a muddle on my truck rebuild and am after your wise help please.<O></O>
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I have search the forum but to no avail, sorry if i have missed the answer.
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I am in the process of converting my 1986 F150 302 manual 2wd to 4x4, not as easy over here in the United Kingdom as donor parts are hard to find. However lucky for me, I was able to get hold of a 1987 Bronco 351w c6 4x4
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turned out the 351w was junk so am keeping the 302, ive sorted the correct 50oz flex plate so we are all sorted there, the front TTB all bolted up and fitted with my already owned rough country 2.5" suspension lift. Front prop shaft fits great no problems. I also replaced my original 9" rear end with the bronco 8.8 rear. (only because replacing the gears is an expensive job over here)<O></O>
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Now for the big question;<O</O
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I have in my shop 2 prop shaft (tail shafts):

- F150 2wd manual 4 speed to ford 9" solid shaft (slip yoke gearbox end and standard CV joint to the diff).<O</O


- Bronco 4x4 transfer box to 8.8 telescopic shaft type (standard CV joint to transfer box via a (i believe they are called) double cardan CV joint and the other end is a standard CV joint to the diff)

am i correct in thinking the bronco telescopic shaft is the correct one to use?<O></O>
Do i need to use the double cardan joint?
Can i remove the double cardan joint and use a single CV join to the transfer box?<O></O>
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I am fully aware either shaft needs to be modified aka shortened or lengthened. I have a specialist near by that will do this for me.<O></O>
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I do hope this all makes sense and someone out there can help me.<O></O>
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Kind Regards<O</O
Truckandute

 

It is my understanding that the Bronco used the double cardan joint because of the steep driveshaft angle due the Bronco's short wheelbase (104 inches).
Since you are installing in a truck (wb is 133 or longer), the standard driveshaft is all you need.

I don't know of any advantage to using a double cardan joint (possibly a disadvantage would be the increased expense of the joint).

Perhaps someone else will chime in.

 

Minor correction to your terminology. You are correct that a double Cardan U-joint is a CV (constant velocity) joint. But a single Cardan is not a CV joint. It's usually just called a U-joint (universal joint).

So if I'm understanding you correctly, your F-150 transmission had slip yoke in the tailshaft and the driveshaft was solid, while the Bronco had a fixed yoke on the back of the transfer case and the driveshaft had a slip joint in it.

Assuming that is correct you definitely need a driveshaft with a slip joint in the truck after you install the Bronco transfer case. Since you already have the Bronco shaft with the double Cardan CV joint you can certainly use it. It might even be slightly better than a standard shaft, but as CountryBumkin said, you probably don't need a CV joint in your truck.

If you do use the CV joint you should make sure the pinion on the rear end is pointing pretty much straight up the driveshaft when it's sitting at rest. Ideal might actually be if there's about a 1-2 degree angle, with the pinion pointing a little lower than the driveshaft, but it should be very close. If it's not you will get vibration.

If you don't use a CV joint in the font of the rear driveshaft, then you need the angles at the front and rear of the driveshaft to be equal. In other words, you want the pinion angle to be parallel to the transfer case tailshaft. That's how you prevent vibration with non-CV joints.

You can adjust the pinion angle by cutting off the spring perches on the axle and welding new ones on at the right angle. You can also use tapered shims between the springs and perches.

Good luck!

 

Tom Woods' web site has good illustrations on double vs single cardan drive shaft angles.




Tom Wood's Custom Drive Shafts - Driveline 101

 

Truckandute - These guys have given you very good advice. I can't think of anything to add, except if you use the drive shaft with the telescoping joint built in, as I agree you should, check the splines of that joint closely. People have a tendency to neglect them and they can get rather atrocious and cause all sorts of strange vibrations.

And, I'll bet both of those vehicles were brought onto Ole Blighty by US military personnel. We used to live on the "proper" side of Watford, which has a US base close by, and I was frequently appalled by the size of one of their old trucks when I met them on a B road. Yikes! And now I drive one of them!

 

Thankyou so much for the very informative responses. Not only do I now know the answers now I learnt a great deal. Thanks again guys.