Quote:
Originally Posted by Keith Seymore
The orientation of the frame is immaterial.
You are trying to establish the "u joint working angle", which is the relationship between the pinion centerline and the shaft (or the transmission centerline and the shaft).
The attached picture is pretty good but could use some explanation:
"Perfect - inline": this is true from a u joint acceleration/deceleration aspect, and would be ideal in theory but not in practice. The issue is twofold: 1) without any u joint working angle the rollers do not rotate inside the cup, causing them to "brinnell" a low spot in the cup and resulting in a disturbance, and 2) there is rear axle pinion nose windup during vehicle acceleration and deceleration, (and in trim height due to cargo loading/unloading) so the shaft doesn't really stay straight during vehicle use.
"Parallel; moderate strain/minimal vibration": This is ideal, with angles equal and opposite and less than 3-7 degrees. However, "strain" is not really the right word choice, as it is not a strain issue but the disturbance caused by the acceleration and deceleration of the u joints as they rotate. The equal and opposite characteristic allows the accel/decal to cancel out (while one is accelerating the other joint is decelerating the same amount) resulting in no disturbance and no vibration, and also provides some windage so that if the angles are set up like this statically then you come closer to the "inline" setting during vehicle use.
"No! High strain/bad vibration": again - it's not "strain" but accel/decal of the joint. Angles higher than 7 degrees are greater than what a single cardan joint can accommodate. Differing angles front and rear do not allow the accel/decal pairs to cancel each other out.
"Absolutely not! etc": the issue here is that the angles do not cancel each other out and are, in fact, additive. "Poor pinion vibration" has nothing to do with this.
I had a really nice write up on how to set this up, copied from an S10 service manual, but it got Photophucketed.
K
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So as long as my drive train maintains the 'parallel' in your drawings, then it does not mater if the the driveshaft is lower at the transmission then the pinion at the rearend.
As for the 7 degrees you mention I'm going to try to get the transmission set to 3 degrees downward and the pinion to 3 degrees upward.
Again I'm using the RideTech StrongArm suspension. This is not a leaf spring setup. So I think the the 'pinion walk upward' during acceleration is not as big of an issue as it is for leaf springs.
For those that have asked the frame is level for all these measurements.