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Thread: Driveline Setup (aka, Pinion Angle)

  1. #1
    Senior Member karlos's Avatar
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    Driveline Setup (aka, Pinion Angle)

    Getting ready to button up my drivetrain and take my first go-cart. Woo hoo! I set up the driveline a few weeks ago, but in looking at at it again I started to question whether the rather steep driveshaft angle (about 6 degrees) was really acceptable. It's usually the case that when things look right they are right. And this didn't look so good. But I set the pinion angle when I did the initial install, and everything I read indicated that the driveshaft angle doesn't matter, so I thought all was well. Turns out the driveshaft angle does matter, and is in fact directly related to pinion angle. Whoops.

    There are lots of old pinion angle threads going back many years. I’ve read through most if not all of them looking for clarity on what specific driveline checks should be made and what the objective of those checks is. Can’t say that I ever really felt like I understood what pinion angle is, how it should be measured, or what end result I should try to achieve. Much of the info out there is conflicting, confusing, and contradictory. Which probably explains why the topic comes up so often but never really seems to converge on any set of consistent recommendations/requirements.

    I spoke to my local drivetrain guy and looked at the public domain info he pointed me to. I’ve tried to collect and condense that info below in an effort to demystify what should be done to ensure proper driveline setup. This all comes from reputable sources and recognized industry experts (e.g., Spicer, Dana, etc.) and is accurate to the best of my knowledge/ability. I didn’t make any of this up. None of it is based on hearsay or opinion. It can all be verified if you’re willing to spend hours doing the research. But I hope I can save others the time and effort by summarizing and posting it here.

    -Karl

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    When setting up a driveline (transmission/driveshaft/differential) there are a few parameters that need to be checked and potentially adjusted to ensure smooth operation and long life. Regardless of the specific configuration (solid axle, independent suspension, etc), the constraints are the same; only the setup procedures will vary. The basic parameters that should be checked are pinion angle and the operating angles at both ends of the driveshaft. Ideally, the pinion angle should be 1 degree or less and the operating angles on each end of the driveshaft should be equal to or within 1 degree of each other, have a 3 degree maximum operating angle, and have at least 1/2 of a degree continuous operating angle. Some definitions…

    - Pinion angle: the deviation from parallelism (measured angularly) between the centerline of the transmission output shaft and the centerline of the differential pinion gear
    - Operating angle 1: the angle between the centerline of the transmission output shaft and the centerline of the driveshaft
    - Operating angle 2: the angle between the centerline of the differential pinion gear and the centerline of the driveshaft


    With the driveline transmitting maximum power, the ideal pinion angle is zero degrees. Meaning that the centerlines of the transmission output shaft and the differential pinion gear are parallel. A deviation of up to 1 degree is acceptable. Note that it doesn’t matter if the centerlines are offset (this does however affect the operating angles); parallelism is what’s important here. Therefore, each of the scenarios below are acceptable (and ideal, as all centerlines are parallel, and all pinion angles are zero).




    More typically the centerlines will not be exactly parallel, an example of which is shown below. This is OK too, provided the deviation from parallel does not exceed 1 degree. So how do we determine that?

    First, we need a consistent way to refer to the slopes we’re measuring. The slope of the drivetrain is measured going from front to rear. A component slopes downward if it is lower at the rear than the front. A component slopes upward when it is higher at the rear than it is in front. When the slopes are in the same direction on two connected components, subtract the smaller number from the larger to find the pinion (or u-joint operating) angle. When the slopes are in the opposite direction on two connected components, add the measurements to find the pinion (or u-joint operating) angle.

    In the example below, the slopes are in the opposite directions (down on the transmission, up on the differential). So we add the measurements. Pinion angle is therefore 0.5 + 0.8 = 1.3⁰. Since this is larger than 1 degree an adjustment is necessary. Achieving a 1 degree reading can be accomplished in multiple ways. If the differential is adjustable the 0.8-degree angle can be reduced to 0.5 degrees. If not, the rear of the transmission can be shimmed up to reduce the 0.5-degree angle to 0.2 degrees. Either way the angles then sum to 1.0 degrees and the pinion angle is within spec.




    However, the way in which you choose to fix the pinion angle will influence the operating angles. It’s possible to solve the pinion angle problem in ways that will make for undesirable operating angles. You want both the pinion angle and the operating angles to be within spec at the same time.

    Remember that we’re trying to accomplish multiple things with the operating angles:

    - angles on each end of the driveshaft should be equal to or within 1 degree of each other
    - maximum operating angle at either end is 3 degrees
    - at least 1/2 of a degree continuous operating angle (this is to prevent flat-spotting the u-joint needle bearings)

    Operating angles are calculated by finding the angle between the driving member and the driveshaft (angle 1) and the driven member and the driveshaft (angle 2). In the picture below the orange line has been added to represent the driveshaft. It’s arbitrarily shown at 3.1 degrees from horizontal.




    Here is a simplified picture with all the relevant angles.




    Operating angle 1 = 3.6⁰. Operating angle 2 = 2.3⁰. These numbers violate two of our criteria: maximum angle of 3.0 degrees is exceeded, and the difference between the two angles is more than 1.0 degree.

    Here’s one possible solution that will get everything in the box. The rear of the transmission has been shimmed up to reduce its angle to 0.2 degrees. Note that this also reduces the driveshaft angle to 2.5 degrees. Pinion angle is now 0.2 + 0.8 = 1.0⁰, right at the upper limit but good.




    Here’s the new operating angle diagram.




    Operating angle 1 = 2.7⁰. Operating angle 2 = 1.7⁰. All three criteria are now met:

    - angles on each end of the driveshaft are equal within 1 degree (2.7 -1.7 = 1.0)
    - maximum operating angle at either end is less than 3 degrees (2.7 at end 1)
    - at least 1/2 of a degree continuous operating angle

    There is a handy online calculator that can be used to do the calculations: http://spicerparts.com/calculators/d...gle-calculator

    Be aware, though, that it does not do the pinion angle check, at least not directly. You may have noticed, however, that the pinion angle is the same as the difference between the operating angles. Keep the difference between angle 1 and angle 2 to no more than 1 degree and the pinion angle will automatically be in spec.




    The only other complicating factor is that, for a solid axle car, the calculations need to account for the fact that the pinion angle changes as power is applied through the rear end. When the car squats under hard acceleration the pinion tends to rise. The amount varies according to the design of the rear suspension. Might be as much as 4 or 5 degrees for a car set up with leaf springs, or as little as 1-1/2 to 2 degrees for a 4-link. For a solid axle car the pinion therefore needs to be biased with upward slope so that the pinion angle and the operating angles are within spec while under load.

    --end

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  3. #2
    Boydster's Avatar
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    Very nicely done. Excellent, clear information. Thanks.

  4. #3
    Seasoned Citizen NAZ's Avatar
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    Very detailed report. As you stated, the reason for all these angle specs is for smooth operation and long life. Most probably don't realize that as the angle of a u-joint increases it varies in speed as it rotates (increases and decreases every turn). The steeper the angle the greater the speed variation. This is what leads to driveline vibration. See the video at: https://www.youtube.com/watch?v=gmV4qwLfOMY for a good demonstration of this. It's a commercial for a training device but does a good job of demonstrating this phenomenon. After watching the video you may wonder why there is a minimum ½-degree continuous operating angle since no operating angle would seem to be better. We want the u-joint bearings to turn a bit so the needle bearings are always picking up grease and spreading it on the races to keep a film of lubrication between the rolling surfaces and prevent flat spotting.

  5. #4
    Senior Member cgundermann's Avatar
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    Great info Karlos; I followed Jeff Kleiner's advice for my 3-Link and have my pinion set 2 degrees down (Harbor Freight sells a real trick magnetic digital angle finder) - so under load it rises in line.
    Last edited by cgundermann; 11-14-2016 at 10:00 AM.

  6. #5
    Senior Member CraigS's Avatar
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    I agree w/ all that info w/ the exception that the operating angles are very small compared to what we get w/ our very short driveshafts. Let's say we agree that we need about 6 inches of solid axle travel. W/ a 3 ft driveshaft (Mustang, Camaro) we might be able to get that and stay within their 1 deg operating angle spec. W/ our short drive shafts, I don't think that is possible. I set my solid axle pinion angle for 2 deg down compared to the trans. I set the trans mount spacers so my driveshaft is maybe 3/8-1/2 inch higher at the trans than the diff. This is because I set my ride height etc so my 6 inches of travel is split about 3.5 bump and 2.5 extension. For us rather than operating angle being important, making sure the u-joints don't bind at full compression or full extension is more important.
    FFR MkII, 408W, Tremec TKO 500, 2015 IRS, DA QA1s, Forte front bar, APE hardtop.

  7. #6
    Senior Member karlos's Avatar
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    No question that compromises will have to be made for other considerations like binding. What appears above represents the ideal state. Probably not too hard to achieve with an IRS, but a live axle has a whole host of other complicating factors. I believe a good approach would be to do the initial setup consistent with the above recommendations and then make whatever changes are necessary to resolve problems brought about by short driveshafts, etc.

    Maybe this pinion angle thing was clearer to others than it was to me. I struggled with understanding where to start, and not having a clear picture of where I was trying to end up. Hopefully the info given above helps in that regard.

    Thanks for your comments. I think we're saying the same thing: use this as a start point and make further adjustments as needed based on the specifics of your setup.

  8. #7
    Senior Member CraigS's Avatar
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    I should also have said that the diagrams really make the whole thing easier to understand. It is a well written article w/ tons of good info.
    FFR MkII, 408W, Tremec TKO 500, 2015 IRS, DA QA1s, Forte front bar, APE hardtop.

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