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Thread: Driveshaft phasing

  1. #1
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    Driveshaft phasing

    We got some great mechanical minds here. I hope somebody has the answers I can't find on any of the driveline websites.

    I have a GMC TOP KICK 28000 GVWR. The driveshaft consists of a 4' straight section with U joints each end, carrier bearing at rear end of it. Then a three foot section with slip spline. Transmission output shaft is near level, I'd estimate 3 degree downward pitch. Differential pinion points almost directly at it at the same angle. Middle U joint is near straight both shafts measure the same 6 degrees with truck parked at 3 degrees. All joints are very nearly straight.

    The internet is loaded with explanations of driveshaft oscillation. I have dealt with driveshaft phasing on Dodge Power Wagon, and many lifted Jeeps. Everything I've seen deals with two u joint driveshafts, where both yokes in the middle section clock identically. Fluctuations in rotation speed are limited to the center shaft & the U joints cancel each other's fluctuation.

    I have a shake in the truck, comes on during acceleration, or uphill, or down. Seems to smooth out on level, new pavement roads.

    I have 6 new tires, 6new wheels. all have been balanced & checked for run out. Numerous mechanics have checked the steering & suspension. Rear springs are new, all brake cans are new. One U joint is new, others show no wear. Truck was a fire truck, has approximately 10,000 miles

    I have tried turning the spline 90 degrees with little improvement if any.
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    Driveshaft phasing

    Single U joints oscillate. Thatís why cars use CV joints on the axles. On a driveshaft, U joints are always 90 degrees out of phase to cancel out those oscillations. But that only works when both are at the same angle (which is why it doesnít work on axles).

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    Re: Driveshaft phasing

    Double cardan joints.
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    Re: Driveshaft phasing

    I would explore drive line angles. We had a truck that would develop a vibration at certain times and found it was a ride height issue with the airbags
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    Re: Driveshaft phasing

    Quote Originally Posted by John T View Post
    Double cardan joints.
    Based on my research, Cardan joints named for some 16th century inventor, are cross joints. CVU joints were used in the front axle on early Dodge 4 X 4 trucks. Two varieties, Bendix-Weiss, and Rzeppa were used.
    It's amazing how smoothly they turn in four wheel drive, even on pavement. The back wheels still don't travel as far as front, so some stress builds.
    Last edited by Willie B; 09-26-2020 at 09:18 AM.
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    Re: Driveshaft phasing

    Quote Originally Posted by farmshop View Post
    I would explore drive line angles. We had a truck that would develop a vibration at certain times and found it was a ride height issue with the airbags
    I see it a lot with lifted four wheel drives. If transfer case shaft isn't parallel with differential pinion, or within a few degrees, it'll shake something awful. It puts a lot of stress on the whole driveline.
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    Re: Driveshaft phasing

    Quote Originally Posted by Willie B View Post
    Based on my research, Cardan joints named for some 16th century inventor, are cross joints.
    Jeep front shafts use them.... So when jeep guys install lifts of say more than 4" ........ They will install one in the back also... eliminating the slip yoke..
    This is the best way to get rid of "lift vibes"


    This also allows you to use a front shaft in back (same length) So if you break the rear shaft or U-joint, you can always put the front shaft in back to get home!


    I put a 3" lift on my Cherokee and got away with just dropping the transfer case 1"
    Did the trick.

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    Re: Driveshaft phasing

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    double joint
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    Re: Driveshaft phasing

    Hmmm..... went through this with a Dodge D600 and found out they mounted their Ujoints just slightly differently (go figure...it's a Dodge) than all the shops were advising me to install, but if you've already tried the 90 degree thing that's covered. The ujoints also sit down in a little cradle in the casting. I've had the U bolts holding the Ujoints in place come loose enough to let them jamb just slightly outside of the bottom of the cradle so loosen them slightly and make sure they are seated right in the bottom. If you've already checked for bent rims, maybe it's time to check for a bent driveshaft. If anyone has dropped a Ujoint in the past, it could have a slight bend. You also say the joints "almost" line up. Did somebody get the splined joint out one spline? If there's a twist in that spline it will also make it impossible to line the joints up properly. Have a good look at the hanger bearing while you're down there... it's another potential culprit.
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    Re: Driveshaft phasing

    I used to do driveline layouts as part of my job at a major fire apparatus manufacturer years ago and TYPICALLY a 2 shaft, 3 joint arrangement works best with the center joint phased 90 degrees from the front and rear joints. The key is obtaining full/near full cancellation of the oscillation created by the first joint's operating angle thru the center and finally rear joint. With 3 joints phasing the center 90 degrees from the front and rear in effect results in half cancellation at the center and the other half at the rear joint. BUT, there are several other factors that play a roll mainly the relationship of each joint's operating angle with the others as determined by transmission/engine angle, differential input angle and angle of each shaft. Optimum joint operating angle for greatest service life is 3 degrees and the minimum recommended (for lubrication and avoid brindling) is 1. A 1 degree operating angle creates a very minimum amount of shaft speed oscillation that could cause vibration issues and still provides movement for lubrication purposes. Another factor to consider is the combined total operating angles of the first and last joints as compared to the center.

    All that said, there are still installations that go against the basics. IIRC, the early Camaro had an 18 degree offset in its 2 joint single shaft.
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    Re: Driveshaft phasing

    Quote Originally Posted by duaneb55 View Post
    I used to do driveline layouts as part of my job at a major fire apparatus manufacturer years ago and TYPICALLY a 2 shaft, 3 joint arrangement works best with the center joint phased 90 degrees from the front and rear joints. The key is obtaining full/near full cancellation of the oscillation created by the first joint's operating angle thru the center and finally rear joint. With 3 joints phasing the center 90 degrees from the front and rear in effect results in half cancellation at the center and the other half at the rear joint. BUT, there are several other factors that play a roll mainly the relationship of each joint's operating angle with the others as determined by transmission/engine angle, differential input angle and angle of each shaft. Optimum joint operating angle for greatest service life is 3 degrees and the minimum recommended (for lubrication and avoid brindling) is 1. A 1 degree operating angle creates a very minimum amount of shaft speed oscillation that could cause vibration issues and still provides movement for lubrication purposes. Another factor to consider is the combined total operating angles of the first and last joints as compared to the center.

    All that said, there are still installations that go against the basics. IIRC, the early Camaro had an 18 degree offset in its 2 joint single shaft.
    Both ends of the 4' long Yokes are aligned. Can't change that without cutting & welding. 3' section I've tried both phased the same & 90 degree. I can't say which is better. My theory is the front & rear joints have very little angularity, I think a few degrees. There wouldn't be much oscillation at this angle. Not sure how to measure the trans & differential angle precisely, to my eye, they are very close to matched.
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    Re: Driveshaft phasing

    Phasing is pretty easy. Each end of a shaft should have its C in the same plane. The next section should have its Cs 90 degrees off the first.

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    Re: Driveshaft phasing

    Transmission /differential angles are checked with a protractor as shown on this page.... unless somebody messed with your springs or motor mounts I doubt that is your issue however.... https://www.hotrodhotline.com/md/htm..._harmonics.php

    Have you looked closely at that driveshaft to see if any old balancing weights have broken off? At a one to one high gear that thing is spinning the same speed as the engine....
    Last edited by whtbaron; 09-27-2020 at 09:45 PM.
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    Re: Driveshaft phasing

    The rear section has no evidence it was ever balanced. The front section is new, the builder says he has never balanced one. It turns about 2000 RPM at 50 MPH not like a car that might turn 4000 RPM. This shake begins at a much lower speed, maybe even under 1000 RPM.

    There are no flat surfaces to measure an accurate transmission angle or pinion. I'll have to dismantle to measure. Got another project taking me away from it right now.
    The question I don't have an answer to is the three U joint shaft. Since the two sections of shaft both measure 3 degrees difference from the ground, I feel I can treat it as a single shaft. The front Universal produces oscillation in the entire two section shaft. Phasing the trans yoke & differential yoke the same should give cancellation. I've tried it both ways, no discernable difference

    I've only studied one similar truck. It's the rescue truck at the firehouse. Not as heavy, similar driveshaft length. It has yokes at each end of each section of driveshaft clocked the same. Since the center universal mates them 90 degrees apart, the yokes at transmission & differential are 90 degrees opposed, the way mine was after refit. Who's to say this is right or wrong
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    Re: Driveshaft phasing

    Quote Originally Posted by John T View Post
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    double joint
    My four wheel drive van has this arrangement in the front driveshaft. Front U joint at differential is conventional cross joint. At transfer case that angle is pretty sharp, like the one in your picture. Oscillation is pretty significant at higher speeds. I had reasoned that was because the angle is too sharp for a single cross joint, as it is in the front steering joints in my John Deere backhoe.
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    Re: Driveshaft phasing

    This guy just uses an app on his smart phone on the top of the joints... I suspect you would have to be very careful depending on the shape of the yokes and casting flash etc. .... you would need a different location to check pinion/transmission angles.

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    Re: Driveshaft phasing

    There might be someone near you that does "driveshaft balancing service" where they put it on a balancing machine. I'm not sure if you've already explored this and find the cost prohibitive, or you just want to do it yourself.

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    Re: Driveshaft phasing

    A very few machine shops near at all. The few there are seem to specialize in something else. Think of it, I might want to ask Zap about it. He has a smaller facility these days, but might point me the right direction.

    To be honest, I doubt balance is the cause. Logic says a balance issue would get worse at higher speed, this comes on at low speed, especially climbing.

    And no, I'd be happy to pay someone to solve the problem.
    Last edited by Willie B; 09-28-2020 at 12:14 PM.
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    Re: Driveshaft phasing

    Quote Originally Posted by whtbaron View Post
    This guy just uses an app on his smart phone on the top of the joints... I suspect you would have to be very careful depending on the shape of the yokes and casting flash etc. .... you would need a different location to check pinion/transmission angles.

    I just tried that with my cell phone.

    Truck frame is sitting parked in the fall line @ a 4 degree angle. Subtracting 4 degrees, I show transmission & differential pinion at 1 degree each, or within a fraction of a degree out of parallel. Both shafts are at 4 degrees, so center U joint is straight. Both ends are at 3 degree angle. At present, the yokes are same front & rear of the assembled two shafts, It was 90 degrees different.
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    Re: Driveshaft phasing

    Quote Originally Posted by Willie B View Post
    A very few machine shops near at all. The few there are seem to specialize in something else. Think of it, I might want to ask Zap about it. He has a smaller facility these days, but might point me the right direction.

    To be honest, I doubt balance is the cause. Logic says a balance issue would get worse at higher speed, this comes on at low speed, especially climbing.

    And no, I'd be happy to pay someone to solve the problem.
    From what I understand, phasing has to do with balancing over a range of RPMs. Rouse Tire Sales in Middlebury, VT looks like they might help you (or you could hear them out):
    https://www.rousetires.com/Auto-Repa...eshaft-balance

    Anyways, hope you solve the problem.

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    Re: Driveshaft phasing

    Quote Originally Posted by Willie B View Post

    To be honest, I doubt balance is the cause. Logic says a balance issue would get worse at higher speed, this comes on at low speed, especially climbing.
    "During climbing: says to me "under load."

    While I have limited background in multiple driveshafts, I would look at anything that can allow changes (deflection) when under load.

    To me, anything with rubber involved, like maybe the hanger bearings?
    If it does it slow speed under load (engine braking downhill) I'd also suspect the same.

    ADD Side note: I have a trailer that transfers "hopping" to the truck at around 35-40 mph.
    I fixed it by not driving in that speed range

    ADD side side note: I'd be super curious to mount cameras pointed at various parts of the driveline to see what goes from smooth motion to erratic (if it's something that can be seen). Would be cool to see something simple like axle hop (rear axle input bouncing up and down from internal binding) or the driveshaft starting to swing wide in the mounts or something.
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    Re: Driveshaft phasing

    Quote Originally Posted by MinnesotaDave View Post
    "During climbing: says to me "under load."

    While I have limited background in multiple driveshafts, I would look at anything that can allow changes (deflection) when under load.

    To me, anything with rubber involved, like maybe the hanger bearings?
    If it does it slow speed under load (engine braking downhill) I'd also suspect the same.

    ADD Side note: I have a trailer that transfers "hopping" to the truck at around 35-40 mph.
    I fixed it by not driving in that speed range

    ADD side side note: I'd be super curious to mount cameras pointed at various parts of the driveline to see what goes from smooth motion to erratic (if it's something that can be seen). Would be cool to see something simple like axle hop (rear axle input bouncing up and down from internal binding) or the driveshaft starting to swing wide in the mounts or something.
    After spending a number of dollars I'm embarrassed of, I have new tires, new wheels balanced tires, new springs, one new U joint, new brake actuators. everything in the driveline & steering has been checked. Not only by me, also by professionals. Thus far I get lots of shoulder shrugging from the professionals I've approached. Rico is now in the middle of a BIG steel fabrication project for the marble quarry. He can't afford any distractions, he suggested Matt, (the driveshaft builder) screwed up.

    I would so like to dump this in someone's hands. I've spent too much to degrade this now to a few local trips.

    I'm not sure I am ready for the technology your suggestion requires.
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    Re: Driveshaft phasing

    Quote Originally Posted by Denis G View Post
    From what I understand, phasing has to do with balancing over a range of RPMs. Rouse Tire Sales in Middlebury, VT looks like they might help you (or you could hear them out):
    https://www.rousetires.com/Auto-Repa...eshaft-balance

    Anyways, hope you solve the problem.
    By coincidence, or none, I came from Rouse. They provided four rear tires & wheels at the onset two months ago, last week they installed two front tires & wheels, checked everything front & rear for run out, and balanced all 6.

    John Rouse asked if I would let him know if I ever figured it out.
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    Re: Driveshaft phasing

    If the new U joints are in line (and the similar truck you looked at are the same way) the only thing left that the builder could have "screwed up" would be if the new shaft is either out of balance or welded slightly crooked. Might be time to check for both. I know I suggested this before, but double check to make sure those Ujoints are down firmly in their saddles... having one slightly ****-eyed will create stresses as they rotate. Dave brings up the hanger bearing again... is there a chance that it's mounting point has changed with all the changes to the drive train? Eg... is it mounted higher or lower in the driveline than it was before?
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    Re: Driveshaft phasing

    I am leaning toward the driveshaft being out of balance or crooked also.
    It seems you have nothing left.

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