Driveshaft and U-Joint Notes

Apr-2018 R. Kwas, updates on-going [Comments added!]


Yoke Alignment/Yoke Phasing


Background:  When one considers details of the Driveshaft, it is once again apparent that there is a lot going on there...  Drive is transferred through three Universal-Joints plus a Spline-Joint which connects Front and Rear Sections.

Early production Driveshaft version was supported in the middle by a Bearing (7), which was soft-mounted to chassis by two small Bushings (5, 6). It's fiddly, but these Bushings can be replaced without removing Driveshaft. 

On Late version, a large surrounding Bushing (9) supports the center Bearing (10).  In this configuration, the Bushing is only replaceable after removing Driveshaft Rear (first) and Front Sections.  The two support systems are not interchangeable as they interface differently with the underbody of vehicle. 

Driveshaft, exploded view, showing Early and Late configurations.  Note similar phasing of Front and Middle U-Joint Yokes

U-Joint Notes: 


Spline Joint: 

Whenever Driveshaft is removed from vehicle for U-joint service, before reinstalling, the Spline Joint between Front and Rear Sections should be well lubricated.  This joint is often overlooked, but it is important as it is constantly working while driving, to take up length differences which occur in the Drivetrain, with Rear Suspension excursions.  The author prefers graphite filled grease for this, as it has more body than simple grease, and the graphite particles soften the blow under fast Drive to Decell transitions.  Although the Spline Joint allows reinstallation at a number of places, there is a preferred on...!  See also: 

Yoke Alignment/Yoke Phasing:  

When reinstalling rear section of Driveshaft into Spline Joint, Front and Middle Yokes should be aligned (or phased) only as shown below.  Any other alignment can result in Drivetrain vibrations which are barely perceptible, but nonetheless present and virtually impossible to locate by anything other than the "What-was-the-last-thing-done?" trick. 

Correct and Incorrect ways to phase Driveshaft sections.  90 Degree misalignment is shown,
but others are possible due to the many different angles the Spline Joint could fit together.  



Thread:  Driveshaft Contacting Crossmember 


Reference info: 

Good U-Joint info...again, there is more happening here, than meets the ear:  [...notice also that the UJs shown in their graphic are correctly phased!]


Good demonstration of what happens at various Driveshaft alignments:



My response to a post asking about fitting a one-piece Driveshaft:

"Spline joint in the center of the two-section Driveshaft accommodates length variation between Gearbox and Diff as Rearend travels up and down with suspension [not unlike the Sagitta action of Panhard Rod!]. You can fit a one-piece Driveshaft only if you also include a spline coupling to also accommodate the variable length factor which would remain! (although I question why you would consider this, and what benefit or improvement you think you might gain from it!!)
Volvo didn't put a two-section DS with spline coupling in their cars for decoration!...there is plenty of solid engineering involved!! Don't take offense, but it baffles me sometimes why guys want to make changes to a well-engineered system! "



External material sources are attributed.  Otherwise, this article is Copyright © 2018.  Ronald Kwas.   The term Volvo is used for reference only.  I have no affiliation with this company other than to try to keep its products working for me, help other enthusiasts do the same, and also present my highly opinionated results of the use of its products here.  The information presented comes from my own experience and carefully considered opinion, and can be used (or not!), or ridiculed and laughed at, at the readers discretion.  As with any recipe, your results may vary, and you are, and will always be, in charge of your own knuckles! 

You are welcome to use the information here in good health, and for your own non-commercial purposes, but if you reprint or otherwise republish this article, you must give credit to the author or link back to the SwEm site as the source.  If you donít, youíre just a lazy, scum sucking plagiarist, and the Boston Globe wants you!  As always, if you can supply corrections, or additional objective information or experience, I will always consider it, and consider working it into the next revision of this article...along with likely the odd metaphor and probably wise-a** comment. 


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