Viberations through different drive shaft yoke angle

Discussion in 'Got gears?' started by job, Oct 31, 2021.

  1. job

    job 77Regal

    Hello from the Netherlands,

    I've had vibrations in my car (77 Regal) for a while, at highway speed.
    Now the angles of my drive shaft yokes are different.
    The pinion/rear end site is leveld and stock. But at the transmision site it is a different angle. The transmision site should be lower, or the engine should rise to get the same level as pinion/rearend.

    Car is 2" lowered at the front. Is that a problem?
    Do I have adjust output yoke angle now by lowering transmission? All shims are out.
     
  2. TrunkMonkey

    TrunkMonkey Well-Known Member

    Do you know how to measure your current pinion and output shaft angles?

    And do you understand correct angles?

    That will help steer the assistance. :)
     
  3. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    http://www.buickperformanceclub.com/Pinion.htm

    Under power, the rear end tilts up approximately 2*. If the rear of the transmission tilts down at say 4*, then under power, you want the rear to tilt up 4*. In that case, you would need the rear end to tilt up 2* AT REST. That way, under power, your drive angles would be equal. That would be ideal. You can measure the angles with a simple cheap angle finder. To adjust, you need adjustable rear upper control arms.
     
  4. job

    job 77Regal

    Don't laugh... I measured it with an app on my phone.:D:D
    I understand the difference in angles. Just what is the limit when you start to notice it while driving.
    When the car is fixed on the floor rearend is zero degrees. What angle should the drivetrain be?
    Also zero?
     
    Last edited: Oct 31, 2021
  5. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    The transmission tilts down most of the time. That is what you should measure first. Did you read the article I linked?
     
  6. monzaz

    monzaz Jim

    Angles....ZERO measurement reference point? You have to have a reference point.
    That is why you reference front u-joint to rear u-joint as this way earth level or the car on any surface does not matter.
    Best to just install upper control arms that are fully double adjustable and you can play and get the angle right where you need it.
    JD Race
     
  7. TrunkMonkey

    TrunkMonkey Well-Known Member

    With the car fully on the suspension, measure the angle in degrees from the harmonic balancer if there is enough flat edge, the transmission pan rail or the vertical end/face of the output shaft. (and factor the 90 degree to get your horizontal angle).

    That is your first reference.

    Then find the flat horizontal plane of the pinion shaft on the rear. You may need to do the vertical face on the U-Joint mount ears and also factor to get the horizontal angle.

    Typically, the crankshaft to the output shaft is a straight line about 3 degrees "down" (flows from front of engine "down hill" to the tailshaft and the (yoke) front union.

    Then the rear needs to be 3 degrees "up" as the straight line starts at the axle and flows "Up hill" to the end of the pinion gear shaft (and driveshaft rear) union mount.

    Drive shaft will slope downhill from the transmission to the pinion. In effect, (and generally) greater angle at the pinion and less at the transmission.

    You need them to be near in plane with each other, as the needle bearing need a small amount of motion in the caps during shaft rotation to prevent brinelling (where the needles barely move and wear grooves in the cap and eat up the needles) and rapid failure of joints. But you do not want angles to be zero in either yoke to the drive shaft.

    Typically 1/2 and no more than 2 degrees. (you can go 3, but I like the tighter angle)

    Buicks with four links are easier to deal with, but if doing engine swaps, other than OEM transmissions and/or rear ends, (and in some cases, rear suspension mods) you may need adjustable upper arms on the rear so you can set the correct pinion angle. (I had to do this on both my '64 and my '68 for all those reasons).

    Be mindful of plunge depth on the front yoke, as rotating the rear in "pitch" axis can leave you with too much or too little plunge, and you don't want to ruin a transmission.

    I use the plastic drive on ramps under all four tires. Jack up the car and put opposing (diagonal) corner ramps backwards so one ramp in front and back is facing opposite directions, and the car has no chance to roll off and the drive shaft can be removed if needed. (I usually am doing pinion angle and the drive shaft is still not installed after transmission/rear end work). This keeps the suspension loaded and makes it easier to get the measurements, and adjust things as needed.
     
  8. job

    job 77Regal

    Yes I did Larry. 3 times ..thanks!

    I also download the Tremtec app to start with. (See on youtube);)

    So when you lowered only your front end then change both angles? front and rear u-joints. Or am I wrong.
     
  9. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    It has nothing to do with lowering or raising suspension height, measure your transmission angle down first.
     
  10. sean Buick 76

    sean Buick 76 Buick Nut

    I could be wrong however I get the impression that all that matters in this case is the angle of the rear end pinion compared to the angle of the transmission (their relation to each other). The front end being lowered changes both those angles equally my but not their relation to each other.
     
  11. TrunkMonkey

    TrunkMonkey Well-Known Member

    Front end suspension does not matter as the moment is on the rear axle and has no effect on the pinion or the front yoke.

    Rear suspension does affect the rear pinion and driveshaft angles as does it's full travel, so the "baseline" is measured with the suspension loaded. And easy enough to have both front and rear suspension loaded, but only the rear must be.

    Since a car is seldom in state of extreme from "launching" or full travel but for fractions of a second, it does not matter in the long term. The whole of driveline angles is for continuous, normal operation with minimal suspension travel. (and the focus on driveline vibration)

    Racing applications are a separate issue, and have some differing aspects when it comes to the travel and settings for maximum traction on launch. Vibration is no longer paramount, but angle limits are still considered so as minimize driveshaft/joint failures.

    With angled joints, there is a cyclic "eccentric" at one or both ends depending on the way the angles are in relation to the centerline of motion (of the drive shaft), and it is hard to describe in words, but military (aircraft maintenance) and also in A&P, taught it regarding PTO shafts, various shafts for helicopters tail rotors and other coupling shafts (similar to drive shafts and U-joints).
     
    sean Buick 76 likes this.

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