DC-Shaft pinion check

[landtank]

I've had a few questions about vibrations and whether or not a DC shaft is the solution/problem.

So I decided to post up how I evaluate the pinion angle to confirm if the pinion is aligned correctly for a DC shaft to operate without any vibrations.

The technical aspect of this is that a DC (double cardan) shaft requires an operating angle at the differential pinion to be 0* +/- 1*.

An easy way to confirm this is to use a digital angle finder like the ones sold at Harbor Freight.

The procedure is to park the truck so that you can place the finder on the pinion flange next to the drive shaft yoke to get an accurate reading.

Then take a reading with the left side of the finder on the pinion flange

and then compare that reading with another one taken with the top of the finder on the underside of the drive shaft tube.

You don't really care about the amount of angle but only the difference between the two.

I took the readings of my son's truck today. When comparing the two readings the operating angle of the front U-joint is .4* well under the 1.0* limit.


Hope this helps

 

[Road Apple]

Reviving an old thread since pinion angle has been a much discussed topic lately.

Good gouge!! Thank you @landtank for posting this and to @Surfdc for pointing it out on another thread.

 

[landtank]

Reviving an old thread since pinion angle is a much discussed topic recently.

Good gouge!! Thank you @landtank for posting this and to @Surfdc for pointing it out on another thread.

I'm glad you found it useful

 

[landtank]

Bringing this back to the top as I’ve had some questions.

 

[Rusty Marlin]

So, how do you fix it if its off?

 

[landtank]

So, how do you fix it if its off?

You have to change you caster correction method.

This is the rub. Focusing on Caster only when setting up your truck can put you in a situation where both types of drive shafts will vibrate.

The zone from 3 to 3-1/2” of lift is were you have to sacrifice caster if you want to avoid part timing the truck.

The safe lifts are 2-1/2” and 4” lifts.

 

[Rusty Marlin]

I had a feeling you were going to say that.....

 

[OGBeno]

Nice Rick. Clearly stated.

 

[uscmas412]

Can I measure this with a newer iPhone that has an inclinometer/gyro?

The drive shaft I get, but the pinion flange reading I can’t figure out.

 

[landtank]

For a DC shaft you want the pinion face to be perpendicular to the tubing. So one reading is taken from the side and the other is taken from the bottom so the measuring device is in the same orientation. Comparing the two readings will give you the operating angle of the front u- joint which should be 0* +\- 1*

 

[oilbrnr]

Can I measure this with a newer iPhone that has an inclinometer/gyro?

The drive shaft I get, but the pinion flange reading I can’t figure out.

If you can place the edge of the iPhone agains the pinion face, then yes, you could use an iPhone. Without crawling underneath mine and just going from visual memory, I'd say no.

 

[Nay]

Used a gravity protractor for years if you don’t want to spend the money on digital or get your iPhone dirty. DC shaft alignment is easy since you aren’t working on ‘equal but opposite’ angles of a traditional u-joint driveshaft.

To add a bit more info, the reason the axle u-joint pinion angle has to be effectively zero degrees is because a u-joint will only rotate at constant velocity (in a circle) at no angle, otherwise it moves in an elliptical path meaning it slows down and speeds up twice per revolution. The double cardan end has two u-joints that cancel each other out so it is a “CV” joint. If you have angle on the pinion end, the driveshaft is now ‘out of phase’ with the DC rotating at constant velocity and the single u-joint end speeding up and slowing down. That’s why the driveshaft vibrates, and to hammer down the most poorly understood point in over 2 decades on Mud, you can’t just pick caster and let u-joint angle follow. Caster is a trailing measurement to pinion angle on a solid front axle that has full time engagement, by definition.

The beauty of the 80 series, and this is unique to my knowledge, is that the stock front driveshaft points up in a broken back configuration. That means a DC front driveshaft conversion adds significant caster because the conversion forces the pinion to rotate down offsetting upward pinion rotation from a lift.

I have 5.5” of lift and an aligned front pinion with DC shaft and zero front driveline vibration.