Confused about wording regarding pinion angles...

[jtszymano]

I see this many times...people say that the pinion should be 1-2 degrees below the output shaft angle.
What exactly does that mean?? ANd is the pinion and output shaft pointed up or down??Keep in mind I am referring to a stock set-up...

For example:
if the output shaft is 3 degrees, what should the pinion angle be?


Please explain the meaning of 'above' and 'below' when it comes to this stuff.
Thanks jTS

 

[Matt]

Easiest way in a 4.0l to get the t-case output shaft angle is to place your angle finder on the valvecover of the engine - this surface is parallel to the t-case mainshaft...

In the case of an OEM style driveline (2 u-joints) you need to have both joints operating at the same angle so the eliptical paths of the joints cancel each other (no vibes) A double cardan joint gets around this by having the two joints right next to each other in the DC joint cancel any vibration.... I digress

This means in the two joint shaft the pinion shaft and the t-case shaft should be parallel in theory (dynamic reality is a little different) So the angle of the driveline tube itself does not matter as long as the joints are not binding (usually less than 14 degrees is good for the road)

However if you set the t-case output and the pinion truely parallel things will be correct under no load - add axle wrap into the equation and folks tell you to under shoot the pinion angle by 1 or 2 degrees to account for the fact that the pinion shaft angle will rise when the power is applied to the rear end...

Make sense

Matt

Edit: for your example; t-case = 3 degrees below the horizontal plane the pinion shaft should then be 4 or 5 degrees (also below the horizontal plane) - so when you hit the throttle you effective angle of the pinion shaft becomes 3 deg below the horizontal plane

Just get a double cardan shaft; point the pinion at the output of the t-case and be done with it

 

[Ralph]

Stock set up looks like this. The t-case output shaft and diff pinion shaft are parallel. The pinion shaft should point up a few degrees to compensate for the torsional twisting of the rear axle when power is applied to the axle.

RR3

 

[Matt]

The pinion shaft should point up a few degrees to compensate for the torsional twisting of the rear axle when power is applied to the axle.

RR3

Oops, I think you mean down a few degrees - right Ralph! - axle wrap drives the pinion and the whole axle housing clockwise around the center of the axle tubes when viewed from the driver side of the vehicle (as in your graphic)

Matt

 

[Eagle]

I agree with Matt. Ralph's diagram is a great pic, but under load the pinion "climbs". Also, if the transfer case out put is considered to slope "down" in the direction of the driveshaft, we usually talk about the pinion angle in the reverse direction, as if we were looking from the pinion yoke forward. Therefore, if the angle at the t-case is -3* (3 degrees down), the corresponding angle at the pinion yoke should be +3* (3 degrees up. You would actually subtract a degree or two from that to allow for the "climbing" effect, so the pinion angle should be set to +1 so under load it will climb to +3 -- it should not be set to +5.

Note that all these discussions refer to the angles of the transfer case output shaft and the pinion shaft. Many articles refer to the "pinion angle" or "u-joint angle" as the included angle between the pinion shaft and the drive shaft. Whenever reading an article on this subject, be sure to understand which terminilogy the author is using.

 

[jtszymano]

Ok, now here's my personal experience.
When I put the 3" leaf pack on last year, with the 3 degree shim...I had driveline noise at 60mph BUT no vibes I could actually feel. I cant remember the exact angles with that set up but I decided to do a little test...
Heres what I did:
I tried to make the pinion exactly equal to the output shaft. And to do this I took the shim off, which made the angles closer but still had noise, just a little more of it.
Then, I flipped the shim around(fat side forward). In this scenario, the angles were practically equal and the pinion looked pretty much paralell to the ground BUT I had noticible vibes!
So I still am confused about the angles.

But right now with the rear at 1.5" and the front at around almost 2", the angles are( I did a UC lift):

Output shaft) 3.5 to 4, I guess to be correct, I should say (-3.5-4)

Driveshaft) around 7.5

Pinion) around 7
Oh I also made a little .25" spacer crossmember drop...
I tried measuring many times as well, and the #'s all came up around the same!! I dont know what do you guys think?

 

[jtszymano]

can someone explain why the vibes were worse when the pinion angle was closer to the output shaft angle(when I flipped the shim to fat side forward). ?

Going by what every diagram I have seen, the vibes should have been practically eliminated...

Please dont respond w/ 'get a sye' thats not what I am looking for, thanks! JTS

 

[Ralph]

Oops, sorry for the SPOBI. I don't know what I was thinking. I ment down a few degrees. The torsional twisting tilts the pinion up. Thanks for catching that, guys.

It sounds like you are on the right track by experimenting with different angles. Check to make sure that the rear is what is causing the vibes by remove the front driveshaft when making your checks.

RR3