Rear drive shaft CV

[Geniusloerts]

From what I gather my rear drive shaft is suppose to have a cv set up on it like the front. I pulled the shaft to get the axle and springs out and this is how it was set up. The universal joint at the transfer case was shot. I think I’ll have to find another shaft or see if adding a cv to this one will work. That sound about right?

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[DirtDonk]

Yes, but you'll need to check the output yoke on the transfer case to make sure it's still the CV style, rather than having been changed out to work with the single-cardan style shaft you have.
If you need one and can't find it locally, we carry this: https://www.wildhorses4x4.com/product/Transfer_Case_Yoke/Bronco_Dana20_Transfer_Case

There were in fact some few very early Broncos (usually only '66 models, but I think we found at least one '67) that were delivered from Ford with single-cardan shafts. They're not supposed to exist, but we know they do from the original owners.

The yokes are different, and the angular expectations at the rear differential pinion are different, so you'll need to make sure it's set up properly for a CV/double-cardan style shaft once you get your replacement.
And I do believe that on Broncos there is an advantage to using the CV style as Ford intended.

That shaft of yours looks a little different from others I've seen too. Just a little odd.
Is this the '71 in your signature? Do you know how many PO's it's had and can you contact any of them still to find out who might have changed it and why?

Paul

 

[DirtDonk]

Oh, and you can't just add a 2-joint centering yoke to your existing shaft. You could probably have a local shop put the correct end yoke on first, if they're available separately (I would assume they are) so the shaft looks like this one posted up in another thread a few days ago:



Paul

 

[Steve83]

It's a double-cardan (DC) joint; not actually a constant-velocity (CV) joint. My shaft's a Woody: http://www.4xshaft.com/ .

 

[Geniusloerts]

Paul,

Thanks for the info. Yes this was on my 71. As far as previous owners The guy I got it from had never messed with it and who knows from there. Judging from some of the things that have been done to this bronco it wouldn’t surprise me if someone “made it work”.

I’ll check out the transfer case flange and assess from there.


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[DirtDonk]

It's a double-cardan (DC) joint; not actually a constant-velocity (CV) joint.

Yep, but double-cardan is just the "type" of CV joint. Not a completely different category.
In fact we talked about this a few years ago, but the double-cardan setup was the very first attempt (successful that is) at making a CV joint. Being a CV is it's whole reason for being.
They took the simple single-cardan (named for some Italian bloke named Cardano) and doubled it up to achieve a near constant velocity at different angles.
This was approx. 400 years ago and the ball-n-socket Rezeppa and other types we are more familiar with are just more modern and more efficient (in some ways) versions of a CV joint.

They have the advantage of retaining more strength at more acute angles, in a more compact package, making them more suitable to steering duties.
We've just been calling ours double-cardans and have left all the other modern iterations to the "CV" category. When in fact the double-cardan IS still a true CV joint.
And the first from what I remember.

I still use double-cardan to differentiate, but if someone calls it a CV it's not technically incorrect.

Paul

 

[Steve83]

DC is a close approximation of CV, but it's not, for the same reason that a single Cardan (common Hooke's-style U-joint) isn't. It's only pretty close to CV under VERY specific geometric limitations, which don't actually exist very often in vehicles. But it's never truly CV because the H-collar between the 2 Cardans is no more CV than across any other single Cardan joint. The DC gets close to CV because the 2nd Cardan in the system has the exact same & opposite inconsistency as the first, so they nearly cancel out. The mass of that H-collar always has some vibration that prevents true CV. That's why true CVs were developed & implemented. If a DC was really a CV, we'd have DCs in the steering knuckles of FWD cars because they're MUCH cheaper & more-robust than ball-type CVs.

The difference is only apparent at high speeds &/or high operating angles, but there IS a difference. Read what this article says about DCs:
https://en.wikipedia.org/wiki/Constant-velocity_joint#Thompson_coupling
Note that even the Thompson coupling (which is a variation of DC) is also not technically CV. It's just a CLOSER approximation because the coupling between the 2 joints (the scissor pantograph) has such low mass.

 

[jamesroney]

Paul, Please note:

A bagel is a close approximation of round, but it's not, for the same reason that a donut (common grease fried dough confection) isn't. It's only pretty close to round under VERY specific geometric limitations, which don't actually exist very often in vehicles. But it's never truly round because the donut hole is no more round than the outer donut. The donut hole gets close to round because the outer donut in the system has the exact same & opposite inconsistency as the donut hole, so they nearly cancel out. The mass of the donut hole always has some blob that prevents true roundness. That's why bagels were developed & implemented. If a bagel was really round, we'd have bagels in the coffee business because they are MUCH cheaper & more-robust than donuts.

The difference is only apparent when you not hungry but there IS a difference. Read what this article says about donuts.:
https://en.wikipedia.org/wiki/Doughnut
Note that even the sesame bagel (which is a variation of the bagel) is also not technically round. It's just a CLOSER approximation because the mean diameter of the sesame (the sesame effect) can be changed if the sesame falls off.

 

[DirtDonk]

That's why true CVs were developed & implemented.

Well, call one a "true CV" or not does not change the fact that the double-cardan was designed as a way to achieve the CV characteristics. At the time then, it WAS a true CV joint as good as they could get, until the much better designs came along.
I never said they were the best, or perfect. Just that they were the first iteration based on then-modern technology.
And the Wikipedia article you linked to does not sway my thoughts much.

I think I get what you're saying, but denying that the double-cardan was an early CV (and a very good one for it's time) is wrong I feel.

TIf a DC was really a CV, we'd have DCs in the steering knuckles of FWD cars because they're MUCH cheaper & more-robust than ball-type CVs.

I doubt that very much for the reasons I mentioned. Size and strength.
Cheaper is undoubtedly true, but they are certainly not stronger in that type of application as we prove every time we shatter one with a little bit too much right foot when the wheel is turned.
They may be stronger in a straight line especially when space permits them to be made beefy enough, but the exponential loss of strength as the angle changes on a cardan joint makes them completely unacceptable as axle/steering joints.
And that does not even address their size.

To make them small enough to fit in that space that is made sometimes tighter and tighter in the modern world, would compromise their strength even more.
And they don't really wear all that well without renewing the lubrication more often (tiny supply of grease around the tiny needles as opposed to a practically flooded reservoir under the boot), so instead of 100k to 150k life expectancy of a modern grease-soaked Rezeppa they'd be lucky to last 50k assuming they didn't explode first.
Not acceptable in today's high-mileage expectancies.

I'll re-re-re-read the article to see if I see where it's not appropriate to call it a CV because obviously you got that message and I did not. But I'm still saying it's a CV for now.
The fact that the very first paragraph in the "History" of the CV joint is about the double-cardan joint that was designed from the original single-cardan joint to develop a CV joint kind of keeps my on my side of that fence.

"The universal joint, one of the earliest means of transmitting power between two angled shafts, was invented by Gerolamo Cardano in the 16th century. The fact that it failed to maintain constant velocity during rotation was recognized by Robert Hooke in the 17th century, who proposed the first constant velocity joint, consisting of two Cardan joints offset by 90 degrees, so as to cancel out the velocity variations. This is the "double Cardan". Many different types of constant-velocity joints have been invented since then."

I'll still call it a double-cardan of course. Just a double-cardan style of CV.

Paul

 

[Rustytruck]

Id rather eat a doughnut or a doughnut hole than a imbalenced driveshaft or a bagel double doughnuts even better but even they go out of shape and balance on the first bite.

 

[okie4570]

No idea why the of four are rotated.....

 

[Crush]

Yall be crackin me up!!!!!

 

[wsager]

You know what's good? I bagel fried like a doughnut and covered in cinnamon sugar. They used to have a place near Michigan State University that was call Bagel Fragel, or something like that, who made these delicious treats. Although I don't know how frying a bagel affects it's roundness.

 

[Steve83]

Well, call one a "true CV"...

IDK why people think putting "true" in front of something changes it. If it's a CV, it's a true CV. If it's not a true CV, it's not a CV.

...the double-cardan was designed as a way to achieve the CV characteristics.

Actually, it was designed to allow a rotating shaft to flex to a greater angle than a single Cardan joint could. CV wasn't the primary concern.

...denying that the double-cardan was an early CV...is wrong I feel.

Then consider what "constant" means in this context. It means that when the input shaft rotates 10°, the output rotates 10°. When the input shaft rotates 1°, the output rotates 1°. When the input shaft rotates 0.1°, the output rotates 0.1°. When the input shaft rotates 0.00001°, the output... That's the concept of CV, and the only concept of CV. The DC does not match that idea.

...they are certainly not stronger...

I didn't say they were. I said robust, which means they tolerate abuse, like having tree branches jammed through them.

...the exponential loss of strength as the angle changes...

The strength doesn't change at all as the angle changes. The STRESS changes because the joint is trying to accelerate & decelerate 8x per rev. That doesn't happen to a CV - the stress is constant (given a constant input torque) because the rotation is constant.

To make them small enough to fit in that space...

Compare the physical size of the DC on a fullsize truck with a V8, granny transmission, & 2-range t-case putting several hundred (if not >1,000) lb-ft of torque through that DC; to the size of one Rzeppa CV on a FWD 4-cylinder commuter car that needs 2 CVs that size to propel itself. The DC is MUCH smaller for the power it transmits.

...that message and I did not.

The message was in the paragraph I linked - not at the top of the page.

...the induced shear stresses and vibration inherent in double cardan shafts. While the geometric configuration does not maintain constant velocity for the control yoke that aligns the cardan joints, the control yoke has minimal inertia and generates little vibration.

That was about the lightweight scissor or spherical pantograph used in the Thompson version of the DC. The common DC used on these trucks uses a control yoke (H-coupling) that weighs more than both its U-joints combined, so its non-constant velocity becomes significant & noticeable. Moreso as the vehicle weight decreases, meaning it shakes more with the same DC vibration. So an eB will vibrate more due to its DC's non-constant velocity than a fsB or F350 would.

 

[66BlueGoose]

I am dying over here, thanks "jamesroney"

 

[DirtDonk]

IDK why people think putting "true" in front of something changes it. If it's a CV, it's a true CV. If it's not a true CV, it's not a CV.

I don't either...

But it's never truly CV because the H-collar...
has some vibration that prevents true CV. That's why true CVs were developed & implemented.

Paul

 

[Geniusloerts]

Some bankers brought my staff some bagels for breakfast Friday. I’d have to say the holes were more triangle than round...

On a side note this is what the flange looks like on the transfer case.

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