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Drive Shaft Replacement


BABABeemer

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I'm in the process of changing the final drive on my 1999 R1100RTP and I can't find any reference in the manual about installing the drive line so that the U joints are in phase? I know that this is an important step while installing automotive drive shafts and some vehicles even have the splines keyed so they only go on one way. Has anyone out there run into this head scratcher? I would hate to get everything installed and end up with some serious vibration in the drive line.

Thanks in advance for any suggestions.

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You are correct,, the service manual doesn't mention the prop shaft alignment.. The prop shaft phasing can make a difference & the greater the shaft U-joint operating angle the more important the phasing of the shaft joints becomes..

 

Not real sure how important the phasing is to the BMW application as the rear joint runs pretty flat compared to the front & neither run at much of an angle until the suspension is extended.. I have seen some come out with odd phasing but not sure they were built like that or ended up like that after service..

 

Here is the correct shaft joint phasing..

 

 

driveshaft.jpg

 

 

Click Link For Shaft Allignment View

 

Twisty

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Is the phasing is critical with the drive shaft shown and not critical between the shaft and the FD? I didn't pay any attention to the phasing when re-attaching my FD. Hope I'm not in trouble.

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Is the phasing is critical with the drive shaft shown and not critical between the shaft and the FD? I didn't pay any attention to the phasing when re-attaching my FD. Hope I'm not in trouble.

If the shaft itself is correctly phased, how it connects to the FD makes no difference.

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Joe Frickin' Friday
Is the phasing is critical with the drive shaft shown and not critical between the shaft and the FD? I didn't pay any attention to the phasing when re-attaching my FD. Hope I'm not in trouble.

 

As Ken points out, the critical issue is the phasing of the front universal joint with respect to the rear universal joint, which should be as shown in Twisty's pic; the yokes at either end of the central portion of the shaft should lie in the same plane (see also pic below; relevant parts highlighted with green lines). The transmission and FD don't care about how they are phased relative to the U-joints to which they connect.

4158.jpg.98cba7fa2cae1e55403e247d8cd9da83.jpg

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Due to a few E-Mails I have gotten on the above U-joint phasing a little explanation here might help..

 

In a conventional U-Joint type carden shaft drive,, each U-joint does not transmit the shaft rotation evenly.. Because the U-joint is driving at an angle to the mid shaft the U-joint causes the shaft that is operated at an angle to the input shaft to speed up & slow down twice as the U-joint goes through a full rotation.. There will be 2 phases of faster & 2 phases of slower.. The more aggressive the U-joint angle the more shaft RPM variation will be present.. A U-joint that is operated at a 0° (no) angle will not cause shaft speed up or slow down.. Nor will a 0° U-joint angle remove the speed up & slow down from a varying speed center shaft..

 

The idea of matching the U-joint phasing is to offset the shaft speed up & slow down by matching the output U-joint to allow the output side to slow down & speed up as the input speeds up & slows down (basically offsetting angles & phasing should allow a fairly constant output RPM even though the center shaft is speeding up & slowing down twice for each revolution)..

 

The less angle the shaft is operated at the less help you get from proper phasing.. If the input & output U-joint angles do not match then proper phasing becomes less important..

 

Ie. If the input U-joint angle is 10° & the output angle is 0° then there will be no advantage to proper phasing the U-joints as the input will be at a constant RPM,, the mid shaft will speed up & slow down due to the 10° input angle but with no angle to the output end U-joint there will be no output U-joint angle to offset the shaft RPM variation..

 

If the input U-joint angle is 10° & the output angle is only 5° then there will be some advantage to proper phasing the U-joints as the input will be at a constant RPM,, the mid shaft will speed up & slow down due to the 10° input angle but with a 5° angle on the output end U-joint there will be some output U-joint angle to offset the mid shaft RPM variation to even out the output speed somewhat but not entirely..

 

To make matters even worse you really can’t operate a U-joint at a 0° or very low angle as the small needles in the U-joint bearing will not move on the U-joint cross so they will brinell the U-joint cross in a very short time due to carrying the torque through the small needle bearing contact area with no needle rolling..

 

The auto industry has addressed a lot of the associated U-joint problems by going to a more expensive (but more difficult to package) constant velocity type joint (CV joint) as that allows a much more linier input to output even with uneven shaft angles & compound shaft angles like on a front wheel drive that is both at full turn lock & full suspension extension..

 

A U-joint drive seems like a very simple way to transmit torque around a corner but if you look closely it isn’t so simple as it seems..

 

 

 

Driveshaft-1.jpg

 

Twisty

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