CV joint on front driveshaft
 

So I noticed what appears to be a CV joint instead of a U-joint on the transfer case end of the front driveshaft. I wonder why Ford is using this design. The transfer case is "new" and not the long-used NVG-271/273. However, it was supposed to be 'stronger' and typically CV joints are not as strong as U-joints.

Picture for those of us vehicular challenged people?

There are two styles of CV joint. The most common for automobiles is the double ball in cage or Rzeppa joint. These are typically encased in a rubber boot and contain high pressure grease since they contain movement in two directions, axial and longitudinal (the same as I will explain regarding the cardan style joint later). They are typically spline mounted with a retainer clip at one end of the shaft and flange mounted at the other and the shaft is married to each end as far as angle and direction. (There are more and more applications using a flange at each end). The other major style CV joint is the double cardan style which is a casting containing two standard U-Joints. This is typically flange mounted at one end (usually the driving end) and also uses a single cardan style joint at the driven end. Ford has used there many times in the past for the front drive shafts and they can afford a greater angle of operation without sacrificing the strength which is common in single joint applications (single joint at each end). These setups require the driven end to be as close to zero degree angle between the shaft and the axis of the driven end as possible and raised or lifted vehicle may have to change the angle of the differential to eliminate chunking, also felt as vibration when operating in 4wd. Those changes unfortunately also bring about steer geometry issues. This is because any cardan style joint creates longitudinal movement as well as a speed change in the shaft within each rotation. The movement is cancelled when using two single cardan joints "in phase" with each other but is none the less there and it is greater with higher degrees of angle. Due to the geometry of the angle created in the joint there is a continual loading and unloading of stress in the trunion of the u-joint which often leads to failure if not adequately sized to accept the torque on the shaft. Using a constant velocity joint at one end and a single cardan at the other will create a "chunking effect" in the shaft, not unlike the axle joint chucking experienced with Fords forever. If the single cardan joint can be kept at zero degree alignment, there is no chunking. The farther a vehicle is raised or lowered whether it is from height modification or suspension compression the more the effect will be felt.

The double cardan style joints are fairly strong. After all, they are indeed u-joints and this style has been used for years, long before the Rzeppa style joint was made popular in the front wheel drive vehicles. GM has long used the Rzeppa joints in their trucks and consequently their 4 wd drive mode is much smoother. Their front shafts also fail more often due to stress. However, if Ford has changed to this style joint in the front drive shaft the gear reduction of the differential should compensate for the lesser strength of the typically sized Rzeppa.

I have sometimes wished that Ford would incorporate the Rzeppa in the axle joints of their front ends but then back out of that desire recognizing the reduction in strength which comes along with that change. Those of us in the north who often times run from snow, slush and ice to meerly wet or even dry roads all within a few short miles would appreciate not having to "shift on the fly" numerous times per trip in order to navigate around corners without overstressing the single cardan joint in the front axle.:-X22

So, what is Ford using up front now.
The same double cardan they have been using or a cv?
Rzeppa joints? Not in my big trucks. How many birfields have I trashed backing up with the wheels turned when rock crawling? I've lost count at this point.

As a guy that builds driveshafts and axles, the gear choice isn't going protect the driveshaft. The lower the gears the bigger the tires.....and so on.

I only say that because the angle on the cv would not be as steep unless on a heavily modified chassis and the higher rpm/lower torque before the gears would give the cv a better chance of surviving. AND if properly sized it could handle all of the above. GM made huge mistakes in judgement by using the same front shafts in their HD trucks as the FWD Cadillacs. But that is GM. Build them cheap and build lots of them.

Here's a pic. Pretty close up but it was the best I could do for now.

The silver ring is the front output of the transfer case.
https://cimg6.ibsrv.net/gimg/www.for...2cb4ac45be.jpg

This will be interesting to analyze. Looks like a Rzeppa style joint with a metal shroud. I wonder if it is lubricated by the transfer case gear oil? Another mystery to solve. Damn, a good parts book would sure be handy in a case like this! Thanks for the pic. Anyone else have ideas?

Probably just grease packed into the rubber boot as usual. If the boot was torn and transfer case oil was the lubricant, the result would be catastrophic failure of the t-case. Just replacing the CV is the cheaper route. However, replacing a U-joint is typically cheaper and easier than replacing a CV.