driveshaft phasing

[old cool]

Sorry for all the questions on the same day. Hope others can benefit from all the expertise on this forum.
I've read a lot about vibration and drive shaft phasing. As I understand it, the front and rear yoke have to be running the same way as they enter input and output points. Kinda hard to explain, but when looking at front and rear of drive shaft, one yoke CAN'T be running east and west while the other end is turned north and south. I get that, but I don't see how they can be a 180 degrees off if they appear visually correct. Questions:

1.) If yokes look same (mirror each other) can they still be out of phase, and if so, how do I determine?
2.)Can I drop drive shaft rotate just one yoke at 180 degrees?
3.)Would out-of-phase yokes be real shaky during the drive? Can they cause mild vibration? I get milder vibration at 30-35 mph. It is felt in floor gear shift handle and steering wheel. I don't really notice the body, front end, or seat shaking.
4.)Since the slip yoke going into the trans has a blind spline, will that only go in one way? Or, can the blind (missing) spline slide in at any position into the tailshaft?

I pulled in a trans shop and was told there were many variables to consider. I do understand and believe this is correct. But, I'm still gonna try a few things just because the hunt and fix is what we old guys do. Last year I started a thread called drive line noise. The responses were so abundant I didn't no where to begin. Hence, smaller, narrowed down questions is my new approach. Thank you for bearing with me.

As always, I am grateful for help. Love the forum.

[Keith Seymore]

Ah - I remember. You didn't memorize this when I attached before:

http://67-72chevytrucks.com/vboard/s...d.php?t=522180



Take a look at this and see if that helps. The u joints should be in the same line, barring an obvious misbuild or damage.

A driveline disturbance can manifest at a relatively slow speed, especially if it is second order (u joint related). It will normally increase, and then decrease or go away completely with increasing speed because the drive shaft doesn't have enough mass by itself to upset the whole vehicle (it must rely on a resonance to create enough energy which, by definition, it passes through). Normally the noise transmission path is structural, up through the springs, into the frame and into the passenger compartment/seat, or up through the shift handle, as opposed to the steering column.

You might be further ahead soliciting help from an actual driveline shop, rather than a trans shop. Dynotech/Balance Engineering is a supplier to GM here locally (Troy Michigan) and has been doing this for a very very long time.

K

[Keith Seymore]

Phasing also used to apply to a driveline "trick" that has now become passe'.

"Phasing" used to refer to the act of intentionally allowing the front joint to lead the rear joint a slight amount, intending to compensate for any compliance in the driveline and as an aid in the u joints canceling each other's acceleration/deceleration cycles. (Think "Kentucky windage").

We don't do that any more, as it was shown to not be very effective and caused a lot of confusion in the field. That's why went back to the straightup approach shown in the document attached above.

K

[old cool]

This is beyond me Keith. And yes I do remember your help. Thank you. The directions back then went straight over my head. lol. I was hoping someone could help me identify the problem based on their own unfortunate experience with vibration and whirring noise. It's kinda awkward to mention it, but didn't even know what a slip yoke was.
Appreciate the name of a resource. And it's local to me.
I am now to the point where I can at least discuss things. For example, I thought if Ujoint caps were both vertical (visually speaking), you were in phase. I also thought the angle issue was based on the trans and rear end being parallel. I better stop here before I really expose my ignorance.
Anyway, thanks again sir; your one of best on the forum. Still want to see your Bonneville. BTW, do you have a person you would recommend. I'd drop a name (yours) in a heart beat if it would help. Be blessed.

[rustbucket66]

The yokes must be in line with each other or phased. When you pull a slip joint or midship yoke apart, make sure you mark how it came apart. The shaft is balanced that way. The yokes are cast, and therefore, can be heavier on one side or the other. The tube itself is pretty much balanced. If you put the yoke or slip joint on 180 degrees out, then you have the heavy side of the yoke or slip joint on the same side the weight is welded on the tube. Now you really have an out of balance condition. That is why it is so important to mark the slip joint or yoke when taking it apart to replace hanger bearing or ujoints. Put it back together the same way. Also, putting a lot of grease or heavier grease in a slip joint will not fix it. You may need to take your drive shaft to a driveline shop for rebalancing, which may be the cause of your vibration complaint.