Why don’t I have a double cardan rear drive shaft?

[cldonley]

Why don’t I have a double cardan rear drive shaft on my 69? Did some come from the factory without, or am I just unlucky? Just ordered the 6 degree shims for the rear axle to get the correct alignment with my lift when I realized something was amiss. Or missing. How badly do I need the double cardan shaft?

 

[Apogee]

You can run a single u-joint shaft, but your rear pinion angle will need to be set accordingly so that the angle at the T-case and pinion match one another plus or minus a degree or two. Short driveshafts like ours tend to do better with a double-cardan at the T-case and the pinion inline with the shaft (or low a degree or two to allow for pinion rise under power), but as with anything, there's more than one way to skin that cat.

Broken back driveshaft configuration anyone? Might be hard to get proper pinion lubrication, but it works on the bench.

 

[okie4570]

All the literature shows double cardan ujoints on either side of the t-case from early 65' thru 77. Some claim that theirs came with a single on the front, some claim theirs came with a single in the back.........

 

[TDubya]

My '69, which I purchased in 2007, has a single in the rear as well. Not sure if it came from the factory that way or PO made the switch

 

[Yeller]

You can run a single u-joint shaft, but your rear pinion angle will need to be set accordingly so that the angle at the T-case and pinion match one another plus or minus a degree or two. Short driveshafts like ours tend to do better with a double-cardan at the T-case and the pinion inline with the shaft (or low a degree or two to allow for pinion rise under power), but as with anything, there's more than one way to skin that cat.

Broken back driveshaft configuration anyone? Might be hard to get proper pinion lubrication, but it works on the bench.

I have “broken back” configuration on mine. It works well, no CV at the tcase, no vibrations, and more ground clearance for the driveshaft. As a disclaimer mine is stockish height with drivetrain mods to keep driveshaft angles manageable

 

[Viperwolf1]

I suspect the single joint shafts got installed after a failure of the double Carden joint and the accompanied cost estimate to replace them. They all had double cardens from the factory.

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[cldonley]

I have “broken back” configuration on mine. It works well, no CV at the tcase, no vibrations, and more ground clearance for the driveshaft. As a disclaimer mine is stockish height with drivetrain mods to keep driveshaft angles manageable

Help me out here-waddaya mean by ‘broken back’?

 

[cldonley]

I suspect the single joint shafts got installed after a failure of the double Carden joint and the accompanied cost estimate to replace them. They all had double cardens from the factory.

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Thanks Viper. I’m building up my 3rd member with a posi and 4.11:1 gears, it’s on the bench right now. I’ve added 2” of lift, running a D20. With the single joint shaft it is obviously significantly shorter. I’m adding 6 degree shims from WH to help with pinion angle. Should I be concerned about the length of the drive shaft?

 

[Yeller]

Help me out here-waddaya mean by ‘broken back’?

Basically making the driveshaft a longer “CV” or “double carden” joint so the oscillations cancel each other out.

Picture explains it well.

 

[Broncobowsher]

In the few years when Broncos were just another old used car...
CV driveshafts are expensive, especially for an old beater used car. I handful of parts, a non-CV driveshaft makes it a driver again for a lot less money. Shakes a little more? Who cares, it runs and drives for cheap.

Fast forward a few decades and that repair is forgotten about, moved through a few new owners, and someone discovers a missing CV. Factory? No. Hack fix back in the day.

 

[DirtDonk]

I’ve added 2” of lift, running a D20. With the single joint shaft it is obviously significantly shorter.

How was the lift achieved? Full rear spring pack, lift block, or add-a-leaf? It might make a difference in angle.
But why do you feel a single-cardan shaft is shorter? The shaft itself would actually be longer in my book, though that does not drastically change the angles you're working with. Nor does it change how you set up the pinion angle.

I’m adding 6 degree shims from WH to help with pinion angle.

Don't add them until you know you need them. Have you been driving the rig this way for awhile and have had no issue so far? If so your pinion angle is probably correct for the single-cardan shaft and may or may not change with the lift. It's a wait-and-see scenario at this point in my opinion.

Should I be concerned about the length of the drive shaft?

No reason to at this point. Most of us don't need new shafts even at 3.5" of lift, and most of the ones that do are due to improper pinion angles anyway!
With single joints at each end it's as simple as measuring the angle of the output shaft of the transfer case, measuring the rear pinion angle, and matching them as close to exact as possible. If needing a little wiggle room, it's best to err slightly to the low side with the rear pinion on these trucks.

And we may never know why yours has a single. As the others have said, all Broncos were supposed to have been delivered with double-cardan shafts at the front and the rear. But it's also been documented well over time that many of them did not come that way according to their original owners.
Now, whether it was indeed done at the factory, or after delivery to the dealership, that would be harder to confirm.

It's very reasonable to think that some PO in the past did not want to pay for a double-cardan replacement, did not understand them (many cases of that back in the seventies through the nineties), didn't like them, or just did not think they were appropriate when they were building up their Broncos.
Then there are instances of dealers changing out rear ends with improper pinion angles (spring perches welded on incorrectly) and creating issues with the pinion angle on a stock unmolested '76 Ranger that a friend's wife bought new in '76. During a subsequent servicing the dealer exchanged the entire rear axle assembly for a brand new one supposedly from Ford under warranty. No explanation was recalled by the owner, but for better than 40 years they changed u-joints about every 5 to 10 thousand miles.
maybe that differential/axle assembly was intended for a single-cardan setup.

But Ford thought the double-cardan made sense, and it seems to have been proven out over time.

Paul

 

[cldonley]

Thanks for all the great info Paul I did a combination of a leaf spring overhaul at a great shop in Austin with some added height plus an add-a-leaf to get to two inches in the rear. The front is a combination of big Bronco springs and WH extreme duty perches, also right at 2”. The front shaft will bolt up but won’t turn, the back won’t bolt up, so I have 4 degree radius arm bushings and the 6 degree shims on the way.

I need 4 new u-joints at this point-before I spend that money I’d like to know if I’d be better off replacing the shafts.

I made the wild assumption (having no experience with the double cardan shaft) that you could remove the double cardan bits and bolt the single u-joint up to the D20, hence shorter.
Not excited about replacing u-joints that often.

Chuck

 

[okie4570]

Thanks for all the great info Paul I did a combination of a leaf spring overhaul at a great shop in Austin with some added height plus an add-a-leaf to get to two inches in the rear. The front is a combination of big Bronco springs and WH extreme duty perches, also right at 2”. The front shaft will bolt up but won’t turn, the back won’t bolt up, so I have 4 degree radius arm bushings and the 6 degree shims on the way.

I need 4 new u-joints at this point-before I spend that money I’d like to know if I’d be better off replacing the shafts.

I made the wild assumption (having no experience with the double cardan shaft) that you could remove the double cardan bits and bolt the single u-joint up to the D20, hence shorter.
Not excited about replacing u-joints that often.

Chuck

I've had my 71' that I wheel with since 2012 and have replaced one rear ujoint that I broke, and can remember seeing one other ujoint break on the trail but wasn't one of the double cardan joints either.

 

[DirtDonk]

I did a combination of a leaf spring overhaul at a great shop in Austin with some added height plus an add-a-leaf to get to two inches in the rear.

Sounds good. No generic way to tell then if the angles are still good, or would have changed substantially.
These days with the new spring packs we just "assume" (but from experience) that almost all 3.5" lifts will require a 6° shim and probably 80% of the 2.5" lifts will too. But with just 2" and a different method of lifting, only directly checking your angles, after the rig is back on the ground and at full weight, will you know what is needed.

The front shaft will bolt up but won’t turn, the back won’t bolt up, so I have 4 degree radius arm bushings and the 6 degree shims on the way.

Why won't it turn? U-joint bind? If so, then adding 4 degree C-bushings is just going to make it worse. Or are you replacing some existing 7 degree bushings with those 4's? If so, then that might be enough, but if you're binding now you may need more than just 3 degrees more to be in the safe zone. Will you be wheeling this rig, or just running around on the street?
Is the front shaft a single-cardan as well? Or just the rear?

I need 4 new u-joints at this point-before I spend that money I’d like to know if I’d be better off replacing the shafts.

Yep, good to find out first. Is the rig back on the ground at this point with the full weight compressing the suspension? Did you measure between the axle and frame to verify the exact amount of lift over stock?

I made the wild assumption (having no experience with the double cardan shaft) that you could remove the double cardan bits and bolt the single u-joint up to the D20, hence shorter.

The end cap of the shaft is completely different and the single-cardan and double-cardan yokes are fully welded to the tube of the shaft. No simple swapping, but if lengths permit, it can be done with the same shaft.
However it really only works in one direction. The shaft's tube is longer on a single joint shaft because the yoke assembly with centering ball of a double-cardan is significantly larger than the standard yoke. So it's relatively easy to convert a single to a double, but not the other way 'round.
At some point it's just cheaper and quicker to buy a new double-cardan shaft and sell your single to someone else.

But be aware that the transfer case yoke is different too. The output yoke for a single vs a double is a different shape and size and design. You can't just get a new shaft and bolt it to the old yoke.
From our company, you need three parts from this page: https://www.wildhorses4x4.com/category/Early_Bronco_Driveshafts
1. The shaft of your choice and length needs.
2. The yoke #8596
3. Driveshaft bolts #8582

You'd only need new u-bolts for the differential ends if your old ones needed replacing. Otherwise they're the same for both shafts because you're not really changing anything at the differential ends.

Not excited about replacing u-joints that often.

You won't need to if the shafts are lined up properly and your need for extended travel is not great.
Nothing wrong with a single-cardan shaft that millions of vehicles have not proven out already over the centuries. A double-cardan simply gives you some added leeway in use, which is why Ford chose the more expensive path, while other vehicles got along with the single-cardan setups.

Either way, your pinion angles, shaft angles and shaft angles need to be matched accordingly. The angles are not the same between the two types of shafts.
But once dialed in, your joint life will be just like anyone else's unless your use dictates something else being needed.

Paul

 

[cldonley]

Why won't it turn? U-joint bind? If so, then adding 4 degree C-bushings is just going to make it worse. Or are you replacing some existing 7 degree bushings with those 4's? If so, then that might be enough, but if you're binding now you may need more than just 3 degrees more to be in the safe zone. Will you be wheeling this rig, or just running around on the street?
Is the front shaft a single-cardan as well? Or just the rear?



Yep, good to find out first. Is the rig back on the ground at this point with the full weight compressing the suspension? Did you measure between the axle and frame to verify the exact amount of lift over stock?



The end cap of the shaft is completely different and the single-cardan and double-cardan yokes are fully welded to the tube of the shaft. No simple swapping, but if lengths permit, it can be done with the same shaft.
However it really only works in one direction. The shaft's tube is longer on a single joint shaft because the yoke assembly with centering ball of a double-cardan is significantly larger than the standard yoke. So it's relatively easy to convert a single to a double, but not the other way 'round.
At some point it's just cheaper and quicker to buy a new double-cardan shaft and sell your single to someone else.

But be aware that the transfer case yoke is different too. The output yoke for a single vs a double is a different shape and size and design. You can't just get a new shaft and bolt it to the old yoke.
From our company, you need three parts from this page: https://www.wildhorses4x4.com/category/Early_Bronco_Driveshafts
1. The shaft of your choice and length needs.
2. The yoke #8596
3. Driveshaft bolts #8582

You'd only need new u-bolts for the differential ends if your old ones needed replacing. Otherwise they're the same for both shafts because you're not really changing anything at the differential ends.

Paul

The front shaft is also a single. I replaced the radius arm c bushings with new stock angle from another vendor a while back and haven’t tried to reinstall the shaft until recently. The u-joints were binding. With all the weight back on the ground the rear wouldn’t bolt up. I decided to regear the third member and replace bearings, do the explorer rear disc swap all together since I needed the shims, so it’s up in the air now. While tearing into the rear gear I discovered I have a Ford track lock, appears to be original from 1969, so at least some good news! I found a used rear double card an from another member on here, so the question then is the value of the double enough to do the swap? I hope to do some moderate wheeling in addition to the rig being my daily.

I also need to check those c bushings to make sure what angle I have.

As usual, thanks for all the great info Paul! Looking forward to the day I can drive up to WH in Lodi and meet y’all.

Chuck.

 

[DirtDonk]

Looking forward to that day too!

At this point, since it's it not possible to even mount the rear shaft, I wonder just how much you'll gain by changing the pinion angle. And the issue still becomes, is that the correct angle for the shaft, or not.
Seems you would be best served at this point by doing a mock-up of the rear end (and the front, but one at a time in my brain!) to see what's going to fit and when.
But for me, the bottom line is your comment about "wheeling it a bit" and at that point I'm a bigger fan of the swap back to a double-cardan than I am making your single work.

But first lets try this. With the vehicle either on the ground, or at least with the weight on the suspension with the axle on jackstands while you work on it, measure the angles on both the output of the transfer case AND the angle of the rear pinion yoke.
With a single cardan shaft these need to be matching angles. Or more accurately stated, they need to be parallel to each other. So if your t-case output is angled DOWNWARD 4° in relation to the ground, and your rear pinion is angled UPWARD 4° in relation to the ground, your angles are dialed-in perfectly.
There is a limited amount of acceptable misalignment of the two, and I want to say it's 2 or 3 degrees from parallel.

With a double-cardan setup the two yokes do not need to be in alignment. You pay attention only (for our purposes of discussion anyway) to the rear pinion yoke and it's relation to the angle of the driveshaft.
Your rear pinion should point almost straight up into the driveshaft. We've found that about 1-2 degrees down from the centerline of the driveshaft is optimal in most cases.

The only time the angle of the upper yoke and driveshaft matter is when it comes to the extreme limits. There is quite a bit of travel/movement in a double-cardan setup, but even they have their limits. If you're near there, then other things need to be done.
But you should not be anywhere near that limit when the vehicle is sitting at ride height with only 2" of suspension lift.

Check all the angles as they sit right now, and see where things stand. If it turns out you need to raise the rear pinion with some shims, that would actually help to mount the driveshaft because the higher angle moves it closer to the transfer case. But if you end up having to turn the pinion down, then no matter what you're going to need a longer shaft.
At that point you might as well go to a double cardan with the new t-case yoke and bolts.

Paul

 

[cldonley]

Alrighty then. Back to the measuring. Thanks Paul!

 

[armynavy17]

I know you already ordered shims, but if 6 degrees doesn't end up being right for your rig, I used http://www.4crawler.com/4x4/ForSale/Shims.shtml and was very happy with the final product. The guys website does a good job of describing the different requirements of singe vs double cardan (not that Paul doesn't, but pictures help sometimes).

I went with 2" x 4.75" and they fit on the spring perch well. My 1.5" lift resulted in a little more than 2" of lift over stock, and I used 5 degree shims with my double cardan driveshaft. As with all things bronco related, results will vary, the only way to know what you need is to measure.

 

[DirtDonk]

Thanks for that link armynavy. Always good to have ready sources for non-standard stuff.
At the old 4wd stores we used to stock every shim angle and width we had available to us. Seemed like no two builds were ever needing the exact same angle. Too much customization for that to work out.

We settled on 6° shims because that worked out in 95% of the stuff our customers were working on. But that was for a fairly narrow bandwidth of modifications. Even with our customers using only our parts, we still have that last 5%!

Be very interested to hear where things fall and what numbers come out of Robinson Texas!
Let us know cldonley.

Paul

 

[cldonley]

Be very interested to hear where things fall and what numbers come out of Robinson Texas!
Let us know cldonley.

Paul

Alrighty, here’s the result of my rudimentary measurements and a rise over run to degrees calculator found on the web:

The aft yoke of the D20 is canted upward toward the rear of the truck at about 6 degrees. The pinion of the third member is canted upward toward the front of the truck about 8 degrees. This puts the angle of the driveshaft and u joints in the “broken back” configuration mentioned by Yeller and Apogee earlier in this thread.

A little history: with the body off the frame i had the rear leaf springs overhauled and added an add-a-leaf for a total of about 2” of lift. Leafs are oriented in the correct direction and reinstalled with new hardware and WH extreme duty links in the back.

All bushings in the front end are new, with (as I recall, it’s been a while) stock c bushings. D20 is mounted on new bushings and hardware from WH. Front is sitting on new big bronco springs (78-79 vintage) and WH extreme duty spring mounts for a total of about 2” of lift. Swapped in a 351W mounted on new stock engine mounts from O’Reilly’s. Original 3 speed and D20.

Body is complete except for glass, a seat and a door, sitting on 1” body lift with repaired body mount perches.

I have a used double cardan rear drive shaft on the way. If I install the 6 degree wedges that will not help my pinion angle, it will make it worse. Does that make sense?

Haven’t measured the D30 pinion angle yet.

Also, just saw your question about driving the rig-it has been under construction for several years but driveshafts we’re fine at stock height (other than having worn out u-joints) before stating the makeover.