Driveline Angles

[lees02ws6]

I have an issue with pinion seal and bearing failure, on an IRS car. I have suspected that the driveline angles were not correct, and research of proper driveline angles has led me to the understanding that component center lines must be parallel (diff and trans must always be parallel in both planes), and have equal but opposite angles. I called both Denny's and Dynotech and they both said that I need to point the pinion down 3°, which is counter to everything I have read to this point. See diagram below. Their suggestions would seem to make the situation worse. As a note I cannot rotate the pinion up any further than 0° to a little less than 1°.



My diagram:



References:

http://www.drivetrain.com/parts_cata..._problems.html
http://www.4xshaft.com/driveline101.html

Educate me. Thanks

[DETON8R]

Take a look at this from the Chassisworks G-Link installation and set up instructions.

As I've come to understand it, the important thing to take away is that the final drive line angles need to look like the "What I think I need" diagram under acceleration and load, and when the car is at rest is what it should look like as suggested by Denny/Dynotech. Remember, the pinion shaft rotates upward or climbs as the driveshaft turns, which changes the pinion angle. And other things affect the "at rest" pinion angle setting, Torque from the engine, traction of the tires, slop in the third member mounting.

I've had some of the same questions, and searching on the internet usually gets you to 4X4 bulletin boards that are discussing the extremes that are encountered in jacking up trucks. There are a few other sources for cars set ups, but you need to look really hard for it.

Again, I'm no expert, but the diagram that is "Perfect in Line" isn't a good set up, as several cars actually have that geometry, and a drive line usually needs a minimum offset (I've seen 2 or 3 degrees, but I don't have a reference for that number) and to accomplish this the gearcase or center section of the third member is actually offset (off center) to one side of the car and is not centered mid-line of the car.

Sorry for any format issues, and thank you to Chris Alston for the explanation.

Pinion Angle
Our recommended pinion angle of one to two degrees down, as compared to the engine crankshaft angle, serves as a starting point for your particular application. Installed components, available traction, and specific application will have some affect on the correct settings for your vehicle.
Pinion angle is to be set at ride height by equally adjusting the upper control arm lengths. Upper arm must be unbolted from the axle tabs and jam nut loosened for adjustment. Be sure to tighten the jam nuts and mounting hardware to the torque value specified in this installation guide.

Understanding Pinion Angle
The pinion angle is a very misunderstood measurement. The pinion angle is simply the difference in degrees of the engine crankshaft or drivetrain angle and the third member. The pinion angle is not a tuning aid. It is something that has to be set, but you do not adjust it for bite.

Measuring the Drivetrain Angle
This can be taken from the vertical surface of the transmission tailshaft, the oil pan rail, or the front face of the harmonic balancer. Most production vehicle drivetrain angles will run slightly downhill towards the rear bumper. A typical measurement may be 2 degrees.

Adjusting the Third Member Angle
The third member should be adjusted so that at ride height there is one to two degrees difference in the measured drivetrain angle and the third member angle. The pinion must point down 1 or 2 degrees from the engine or drivetrain angle. As an example, the two degrees downhill drivetrain angle
previously established would require the third member to be set at zero degrees or parallel to the ground for a difference of two degrees.
Lengthening the upper control arms to tilt the pinion upward to a measurement of one degree would give a difference of one degree when compared to the drivetrain angle.
Greater traction from wider or softer tire compounds combined with higher horsepower levels will require a greater pinion angle than low traction, low horsepower applications. The object is to get the two angles to be equal during acceleration. A poly-bushing link is more compliant and will flex more than the pivot-ball link, so poly links may require more initial pinion angle.