Driveline angle and u-joint working angle

Discussion in 'Transmission & Driveline Topics' started by Knuckle Dragger, Aug 30, 2020.

  1. Knuckle Dragger

    Knuckle Dragger Mayor of Simpleton Staff Member Lifetime Gold Member

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    OK, I think I'm inside my own head here. I'm chasing a vibration on my 1994 C1500 short bed truck. I suspect it's just the empty bed hop at this point but I decided to upgrade to a 5 inch aluminum shaft (thanks Tahoe donor) and have a look at the drive line angles.

    Looking from the drivers side and following the slope front to rear the Trans angle is 6.7, drive
    line is 2.7 and the pinion is 6.4 , all sloping down or toward the back of the truck. This gives me a working angle of 4 degrees on the front joint and 4.3 on the rear joint. I can't find a definitive answer on acceptable operating angle or is the difference of .3 is enough to be an issue.

    It seems the rear pinion angle can be expressed two different ways and mean the same thing, this was my method:


    What's the consensus?
     
  2. muscl car

    muscl car Veteran Member Lifetime Gold Member

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    Dave ....


    When i was talking with Currie enterprises for a Ford 9" build we discussed pinion angles and transmission tail shaft angles . The tech i was talking with mentioned 1-3 degrees at the tailshaft and 1-3 degrees at the pinion
     
  3. Knuckle Dragger

    Knuckle Dragger Mayor of Simpleton Staff Member Lifetime Gold Member

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    That's what I'm thinking after reading everything I can find. I'll change both the trans and the pinion to get them to match dead on as well as try to get the working angles as close to 1 degree as possible. I'm going to order the axle shims today, I should be able to make something to shim the trans up. The joy of a truck us there is all kinds of room in the tunnel.
     
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  4. camaro71/holland

    camaro71/holland Veteran Member

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    One thing I've remembered after reading some comments from knowledgeable people, was to remove the driveshaft from the vehicle and hide it when working on drivetrain angels. It's got nothing to do with the result and only adds to the confusion.

    It's all comes down to two angles: engine/transmission measured from the balancer and the rearend/pinion measured from the yoke.
     
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  5. xten

    xten Veteran Member

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    Is the vibration constant or is does it happen under harder acceleration? Is the truck lowered?
     
  6. Knuckle Dragger

    Knuckle Dragger Mayor of Simpleton Staff Member Lifetime Gold Member

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    75 MPH give or take, I notice it on cruse, throttle on or off doesn't seem to effect it, nor does going to neutral. Definite speed related and it's in the seat, not the wheel. Drive shaft RPM at about 3400. Truck is lowered and the kit said it corrected for drive line angle but I never measured it. Cannot duplicate on jack stands. Once I get the drive line angles correct I will be using an electronic vibration analyzer and software to isolate the frequency. I figured since I had it off the ground I should measure the angles and see what I was working with and make the corrections as needed before I proceed with more diagnostics.

    Absolutely not the driveshaft itself, tires, wheels and I've confirmed with the new shaft we are well outside the half speed harmonics.

    Any opinion on the working angle of the u-joints?
     
    Last edited: Aug 30, 2020
  7. muscl car

    muscl car Veteran Member Lifetime Gold Member

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    G72Zed likes this.
  8. Knuckle Dragger

    Knuckle Dragger Mayor of Simpleton Staff Member Lifetime Gold Member

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    Looks like the answer was right on Spicer's calculator if I clicked the information tab.

    https://spicerparts.com/calculators/driveline-operating-angle-calculator

    Rule 1: Universal joint operating angles at each end of a driveshaft should always be at least one-half degree


    Rule 2: Universal joint operating angles on each end of a driveshaft should always be equal within one degree of each other (one half degree for motor homes and shafts in front of transfer cases or auxiliary devices)


    Rule 3: For vibration-free performance, universal joint operating angles should not be larger than three degrees. If they are, make sure they do not exceed the maximum recommended angles.

    Parts are ordered so we'll see next weekend if it has anything to do with the vibration.
     
  9. G72Zed

    G72Zed Veteran Member

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    FWIW , I have seen used/undamaged and even "newly" built driveshafts that were supposed to be balanced needing work to get them in tune, balanced OK, but runout was off on both ends and in the middle. Wasting time chasing our tails on other places assuming the new shaft was right/balanced in the first place, it was not....

    I have been told, and have seen here is a certain amount of "feel" that goes into balancing a shaft, the operators experience comes into play on this.

    muscle car, great link....thanks for sharing that one, for leaf's, it's also important to take into account what type of bushing is used in front, and the springs designs/stacking in the front portion. It can get confusing as the instructions state the specs in a static state, but must be right in a dynamic state, depends on a lot of variables.
     
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  10. biker

    biker Veteran Member

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    May be unrelated, because I think you had this vibration with the steel driveshaft too, but I think GM has a gearing cutoff for using aluminum driveshafts. Use of a numerically high rear gear with an overdrive trans makes for very high driveshaft rpms that aluminum doesn't do well with. I don't know what you have for a rear gear, but I would think even a 3.73 with a smallish tire, in overdrive at 75mph would create driveshaft rpm high enough to magnify any balance issue you you might have.
     

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