Driveshaft Phasing?

[oilhead110]

I understand the driveshaft phasing and I have looked at 3 K100RS shafts including a new one at the dealer and none were perfectly phased. All were off perfect alignment by about one tooth. Is this acceptable?

Thanks

Dale C.

 

[hhshort]

So maybe I don't understand phasing. K100s only have one ujoint.

 

[krpreston]

U-joint phasing, (timing).

I've been trying to figure out just what you're asking, but as hhshort intimated, phasing is only an issue with pairs of u-joints).

 

[roncooper]

So maybe I don't understand phasing. K100s only have one ujoint.

I think the 4 valve K100s with paralevers have two joints. My 75 with monolever has one.

 

[98lee]

4 valve K100RSs have paralever rear suspension. Paralever driveshafts are 2 piece with a u-joint at each end and a spline in the middle. If the splines are not put back together in the proper tooth, the universals will be out of phase (alignment).

You are correct about early 2 valve K100RSs and all K75s with swing arm rear suspension. There is only 1 universal on those driveshafts. No phasing is involved.

 

[oilhead110]

Phasing

I think the 4 valve K100s with paralevers have two joints. My 75 with monolever has one.

Correct, it's a 1991 4 valve Paralever. It has a 2 piece drive shaft unit.

 

[bikerfish1100]

As Lee indicated, phasing does not occur until the front portion of the driveshaft (attatched to the transmisison) is mated to the rear half of the driveshaft (attached to the rear drive hub). Beyond that, there is no phasing. When you line the half-shafts up inside the paralever/swingarm, you have to use a steady eyeball to align the parts. Not sure if most eyes can detect one-tooth off or not; but I/you do the very best you can.

so where are the shafts "out of phase" that you looked at? Were they offering used ones for sale, both front and rear sections, together?

 

[oilhead110]

Phasing

As Lee indicated, phasing does not occur until the front portion of the driveshaft (attatched to the transmisison) is mated to the rear half of the driveshaft (attached to the rear drive hub). Beyond that, there is no phasing. When you line the half-shafts up inside the paralever/swingarm, you have to use a steady eyeball to align the parts. Not sure if most eyes can detect one-tooth off or not; but I/you do the very best you can.

so where are the shafts "out of phase" that you looked at? Were they offering used ones for sale, both front and rear sections, together?

I have looked at two used para lever shafts and one new one at my dealer. They were all approx one spline tooth out of being perfectly aligned. The dealer service manager said it was nothing to worry about. I was just curious, does it have to be perfect or is one tooth out too much.


Dale C.

 

[LOSTBOY]

Driveshaft Phasing

I have never seen a BMW driveshaft that could be assembled in perfect phasing; they are always off by about one tooth.

Driveshaft phasing was not discussed until just a few years ago and in reality it doesn't seem to be an issue.

 

[oilhead110]

Phasing

I have never seen a BMW driveshaft that could be assembled in perfect phasing; they are always off by about one tooth.

Driveshaft phasing was not discussed until just a few years ago and in reality it doesn't seem to be an issue.

That's what I suspected.

Thanks

Dale C.

 

[deilenberger]

If you get the phasing 90 degrees out - it indeed will be an issue. You'll feel a strong vibration from the driveshaft as the shaft accelerates and deaccelerates. BTDT on a car once.

Phasing is done to keep the speed of the driveshaft consistant when the U joints are angled. Unlike a "constant velocity" joint - a U joint changes velocity between the two halves as it turns when it is angled, which is why there are CV joints. If you have dual joints on a shaft - you can put them in-phase to eliminate the change in speed between the ends (the center between the joints will still be changing speed.) If you have two joints out of phase - you'll double the effect - and it can be quite noticeable (especially with a driveshaft running at steep angles).

If the joints aren't accurately in-phase, and the sliding joint is between the two ends, try rotating one end 180 degrees, sometimes this is all that's needed to get them phased correctly.

I'm not intimately familiar with the K bike paralever driveshaft, but looking at the picture in REALOEM http://www.realoem.com/bmw/showparts.do?model=0532&mospid=47928&btnr=26_0116&hg=26&fg=05 it appears to be a two piece shaft with a sliding joint. If so - be worth trying a 180 degree turn of one end.

Some info:
http://www.4crawler.com/4x4/CheapTricks/Driveline-101.shtml
http://trailer-bodybuilders.com/mag/trucks_every_shop_know/

I believe Paul Glaves did an excellent article on this subject in the ON about 4-5 years ago..

Calling Paul Glaves to the white courtesy phone.. Paul?

 

[PGlaves]

As I wrote in the piece I did in the ON - phasing is important - but how important depends!. The accelleration/deceleration through the universal joint is real and significant if greatly out of phase. It is miniscule and minimal if a few rotary degrees off from perfect.

Like life itself - do the best you can. If the machining of the splines means you are a fraction of a tooth off from perfection so be it. It won't make much difference. But if you are perfectly out-of-phase at 90 degrees off it will make a difference - whether BMW, Clymers, Haynes, or Wally the Wrench take note of it or not. None of them wrote the book on drive line dynamics. Neither did I, but at least I read it.

 

[98lee]

The following was lifted from an article about 4 wheel drive driveshafts, but it still applies. Unfortunately the illustration did not appear.:


Phasing:

Phasing is a term that describes the alignment of the single-cardan joints on opposite ends of the drive shaft. As discussed above, a single-cardan (or u-) joint does not rotate at a constant velocity if the operating angle is non-zero. The drive shaft speeds up and slows down slightly as it rotates due to the nature of the joint. One way to reduce this is to make sure the joints at each end of the drive shaft are aligned properly. If the yokes on each end of the shaft line up with each other, as seen indicated by the light blue line in the figure below:



Then the affect will be that the two joints will tend to cancel out the speed variations from each other. In most 4x4 applications, the drive shaft will have a slip yoke in the middle to allow for changes in length. If the shaft is ever taken apart, it is important to get it re-aligned properly when it is re-assembled. One way to do this is to mark both sides of the slip yoke. However, you should check that the joints really do align properly, don't assume they are. The reason for the phasing is that the speed variation of the joint is related to its operating angle and its angle of rotation. In order to get the most effective cancellation, the joint yokes *must* be aligned exactly with each other and the operating angles must be identical. Any variation in either angle will show up as uncancelled vibration. While unequal operating angles result in a vibration that increases with shaft RPM, phasing problems may be felt at lower RPMs and higher loads, like when accelerating from a stop.

Most driveshafts will have some sort of alignment mark stamped or painted on to indicate the proper orentation of the slip yoke. If there is none, they try lining up the u-joint end caps as close as possible. One trick that can sometimes help with phasing is to spin half of the driveshaft 180 degrees before re-installing it to see if this makes any difference. Often one orientation may balance out better than the other. Once you find the proper alignment, paint a mark on both sides of the slip yoke so that you can get it back together correctly next time.