Pinion Angle

For those that were involved in the pinion angle discussion or anyone that cares.

Disclaimers.
The angles etc I use here are just for discussion not "GO BY" numbers.
The angles etc I use here are NOT compensating for anything...uneven lift, ride height.
I'm only doing this to clear up (hopefully) the specific discussion we had this weekend.

My impala sat with the tailshaft down approx 2 degrees.
(Can you change this? yes, slightly, BUT...Overlooking the ability to shim it at the support etc....we move on)
The rear was adjustable, so the question came up....where do you want it.
The observation was made that every pinion witnessed tips downward.
SO...what should we do?

You want the 2 angles of the fore & aft u-joints to be equal.
SO....
If the tailshaft was 2 degrees down, you'd want the pinion 2 degrees up....BUT
THAT disagrees with the observation.
Not really....if theyre BOTH 2 degrees then the pinion angle = ZERO (thats NOT what you want)
Now you want to SET your pinion angle
This is where the observation comes to light.

Here's the Recommended Pinion angles (by the pinion angle guys not me)
Full Solid Mount Suspension = Neg 1 to Neg 1.5 degrees
Half Solid / Half Poly = Neg 1.5 to Neg 2.5 degrees
Full Poly = Neg 2.5 to Neg 3.5
Full Rubber = Neg 3 to Neg 4.5

SO.....
With my pinion 2 degrees up I have to adjust downward Neg 2.5 to Neg 3.5 (Full Poly) to get the proper pinion angle
THAT points my pinion down (Neg 0.5 to Neg 1.5) as expected.

I THINK I've made this easier to understand....Hopefully I'm right here. I'm pretty confident.
Bottom line is, you want to avoid Positive pinion angle and want as close to ZERO as possible on full launch.

Yes, we did need Glenn there ....hopefully if I'm wrong above he'll post

Would it be easier to set if you shimmed your tranny mount?

I don't know how deeply you want to get into theory on this subject.
There is a surprising amount of interesting science being played out in an operating automobile drive-shaft system.

Proper U-joint angle is "engineered in" as an acceptable "evil" for the interests of needle bearing longevity.
The caps & cross will "brinell" if the angle operates less than 2 or 3 degrees of included angle, so this keeps the needles rolling back & forth inside the caps.
Excessive operating angles however will impede efficient power transmission. More angle = equals more lost power.
The operating angles will also modify the output RPMs two full cycles (fast & slow) per revolution.
A constant speed (RPM) driving yoke will deliver mathematically oscillating (angular velocities) to the driven yoke or shaft proportional to U-joint angle.
The idea is that the correctly phased second yoke "COUNTER-corrects" the varying shaft-tube speed fluctuations imparted at the tranny's tail-shaft working U-joint angle.
The desired result is that when the pinion yoke is driven at a constant velocity, even if both U-joints are working at 3 or 4 degrees each, they should be correctly phased to each other.
In this case, the driveshaft is speeding up and slowing down TWICE per shaft revolution, but the trans out-put & the pinion are turning at a constant RPM.

To help you understand this concept, assemble two 1/2" drive ratchet "universals" & some long extensions,
and play with them on your bench, rotating them through various experimental configurations of combined and/or conflicting operating angles.

I believe the F.S.M. has a darn good section showing the how and why of trouble-shooting these driveshaft - U-joint angle issues & set-up procedures.

toomanytoyz wrote:

Would it be easier to set if you shimmed your tranny mount?

I still had to understand where to set the rear.
If I had shimmed the tranny mount to give me say ZERO degrees at tailshaft then yes, it would make setting the angle easier.
THEN all I'd have to worry about the pinion yoke angle.
That being said, I have NO clue how easy it is to regain say 2 degrees at the shaft or whether preloading the motor mounts is a good idea.

Machine-De-Zine wrote:

I don't know how deeply you want to get into theory on this subject.
There is a surprising amount of interesting science being played out in an operating automobile drive-shaft system.

Interesting point about the angle being needed for rolling needles.

I WAS trying to avoid the theory & get to the pinion angles for dummies crib notes.
Could you make enough sense out of my write-up above to confirm or deny its validity?

Another question....concerning our 4 link
How much does the pinion angle change as the suspension moves from compression to extension?

Machine-De-Zine wrote:

I believe the F.S.M. has a darn good section showing the how and why of trouble-shooting these driveshaft - U-joint angle issues & set-up procedures.

One of our members did present the manual....I didnt want much to do with it at that point....shame on me.
I've looked into this a few times, always coming up just short of full comprehension.

Most threads I feel shmart. ..... This ain't one of them.