Re: U-joint phasing and drive shaft theory (long)

[IHMagellan@domain.elided]

Bill is right about the phase.  Additionally, whether the u-joints are in
phase or 90 degrees out, with a theoretically perfectly balanced driveshaft,
the center of mass does not go in circles around the geometric center.  And
don't try to argue that theory and reality aren't related.  You're trying to
achieve the model by balancing, and putting the u-joints 90 degrees out of
phase will only add another problem, not solve the original one.

Jerry Muncie

In a message dated 98-02-10 20:57:57 EST, you write:

<< Bill,
 
      That's close about the speeding up and slowing down, except 
 for one fact.  If you have the yoke in phase, meaning that if you 
 draw a straight line from the center of one side of one yoke, 
 down the entire shaft and to the center of another side of the 
 opposite end's yoke, this line should not be drawn along the side 
 of the shaft.  If you put a bar in one yoke as if to turn the 
 driveshaft, a bar placed in the other end, should be at 90 
 degrees when viewed down the axis of the shaft.  Thus the 90 
 degree phase.
 
      Anyway, now that you're confused (I hope not though), the 
 key to keeping the drive shaft from vibrating is the center of 
 mass of the shaft.  The axis of the shaft actually moves ever so 
 slightly when at an angle.  The problem is when the u-joints are 
 not phased (bars are parallel when placed throught the yokes) the 
 entire center of mass revolves around a radius that leaves an 
 offset (eccentricity) somewhat deviated from the center line axis 
 of the shaft.  If the yokes are phased, then the shaft ends will 
 oscillate around this eccentricity, BUT, the center of mass, 
 stays at the geometric center.  This allows the ends to cancel 
 eachother out and minimize vibration.  The reason the Double 
 cardon CV joint is out of phase at the ends, and in phase for the 
 shaft itself, is that there is a ball in the center of the CV 
 that keeps the eccentricity lined up with the centerline while 
 rotating.
 
      I wish I had a piece of paper to show this.  If the joints 
 are set a 0deg. phase the drive shaft will actually act most like 
 a jump rope, all the mass revolves around a center line.  Where 
 if the joints are 90 deg phased, then the shaft acts like it's 
 suspended at it's center and the ends make circles, like two 
 cones connected at their vertices.
 
      I really hope this helped, if not, I'll try to figure out 
 another way to explain it.  I played alot with the Chev when I 
 had it.  Since it was a 127 in. Wheelbase, and a mated T/C, the 
 rear shaft was 6'6" long and the front was about 29".  The 
 Travelall with the divorced T/C looks to have almost equal length 
 shafts front and rear.  Also the Chev had a 3" rear shaft, so 
 when it wiggled, you could really feel it!
 
      Thanks for the Trans info, I'm working on a game plan now. 
 
 -Joel Brodsky
 
      '76 Scout II 345/tf727
      '75 T'all 150 4wd 392/tf727
 
 -----INCLUDED MESSAGE FOLLOWS-----
 ------------------------------
 
 Date: Tue, 10 Feb 1998 14:33:36 -0700
 From: "Bill Thebert" <bthebert@domain.elided>
 Subject: Re: U-joint geometry, A/T removal
 
 Joel Brodsky writes:
 
 >      About the phasing, you are correct.  Whoever has rattles, 
 > make sure the yokes on the ends of the drive shaft are 90 deg. 
 > out of phase.  If they are in phase,then the whole shaft 'floats' 
 > and rattles your fillings out. 
 
 Joel:
 
 Perhaps I missed the beginning of this thread, but this is contrary to
 everything I understand about U-joint construction and operation.  
 
 The motion of a bent u-joint is "non-uniform" -- that is, if the "driving"
 shaft is rotating at a perfectly consistent 100 rpm, the "driven" shaft on
 the other side of the bent joint will actually be speeding up & slowing
 down twice per revolution.  Sure, the driven shaft still *averages* 100
 rpm, but the motion is not uniform.
 
 The purpose of the "equal and opposite" u-joint angle rule is to reverse
 this process.  By inputting an irregular, non-uniform motion to another IN
 PHASE u-joint at the very same operating angle, the driven shaft will have
 a resulting *uniform* motion equal to that of the original "driving" shaft
 in the paragraph above.
 
 Putting the joints 90 degrees out of phase will compound (double) the
 non-uniformity of the driveshaft motion rather than "neutralize" it.
 <tranny info snip>
 
 Good luck.
 
 Bill Thebert
 The Binder Bulletin
 http://www.binderbulletin.com  >>