One More Drive Line Angle Question

[flip1216]

I am a bit of a simpleton, so the use of layman's terms or small words is greatly appreciated. I know there are multiple threads on the topic (and have read many of them), but I am still left with one simple question:

In order to get the differential pinion at 1-2* down (down meaning the pinion is lower than the back of the differential itself), then the crankshaft/transmission output must be at a positive 1-2* up (meaning the transmission tail would be slightly higher than the crankshaft pulley).

This would give the desired 2*, would ensure the u joints are 'opposite, but equal', and would also disregard the driveshaft as Jeff Kleiner suggests.

Is this correct? Am I missing something?

For what it's worth - MkIV, Gen 2 Coyote, TKO 600, 3-link rear end

[NAZ]

https://www.youtube.com/watch?v=Idk3BVDVHq4

You want the u-joint angles to be the same under load (acceleration). But on most cars and trucks the control arms have elastomer bushings that allow some axle rotation under hard breaking and acceleration. And it's common that unequal length control arms (upper and lower not traveling in the same arc) also allow the axle to rotate causing the pinion angle to change. To compensate for this, most will set-up their static pinion angle with a slight offset of 2-3 degrees. So if your trans output shaft is sloped down at the back 2-deg from horizontal you may set the pinion angle at zero degrees (meaning it is exactly horizontal) which will allow the axle rotation to bring the pinion angle closer to the same ange as the trans output shaft.

Now is it 2-degrees or 3-degrees or what is the magic number? That is a discussion I'd enjoy being a part of but truth is, most people just guess or follow a recommendation from someone else. The proof is in the absence of out of phase vibration.

Click the graphic below for a larger view.

130631


Video of pinion angle change during acceleration and the reason for angle offset when setting static angle. https://www.youtube.com/watch?v=sAfCBwVkyBg

[CraigS]

It may be just your wording so I apologize if this off base. I want to clarify that when you say this, '(down meaning the pinion is lower than the back of the differential itself)' you are not looking at this as a position of a component. This is about angles. Same here, '(meaning the transmission tail would be slightly higher than the crankshaft pulley).' In other words we are not looking at how high off the floor the trans tail is vs how high the crank pulley is off the floor. Also a hint. Depending what type of angle measurement tool you have I find it easiest to look at both angles from the same side of the car. I measure the engine at one of the pulleys, which ever is easiest to get to since they will all be the same. I measure the diff at the heads of two of the cover bolts (assuming all bolts are the same). Also since we are measuring just a couple of degrees off of zero, be sure your tool doesn't switch from a + to a - without you realizing it. In fact I usually just jack up the rear axle by the axle itself (jack stands as safety but not supporting the car) and leave the front tires on the ground. I find it is a lot easier to have the engine measure say 5 degrees and the diff measure 3 degrees.

[GoDadGo]

Flip,

We are all simpletons in one way or another so don't fret because this issue gives many of us trouble.
Just remember as we gain experience and knowledge, we are then able to help others.

Steve

[flip1216]

Naz/CraigS/GoDadGo - thanks for the quick replies and words of encouragement.

Naz - for clarification, we are attempting to get alignment *under load*, not while *at rest*? I ask because the only way to get the parallel alignment, as depicted in the picture you provided, *at rest* (how/when I would measure it) is to either have the transmission tail high (in relation to the crankshaft pulley/harmonic balancer) and the pinion 'nose' low (in relation to the back of the differential) ...OR to have the transmission tail low and the pinion 'nose' high. In my mind, if I don't do this, the angles will intersect, again *at rest*, instead of being parallel, thereby causing vibration. If the angles intersecting is okay *at rest* in order to accommodate a parallel alignment *under load*, I get that.

CraigS - thanks for the quick tips. My descriptions were in relation to the car if we were to run a line down the side of it through the components, not floor heights, heights from the frame, etc. (Clarifying to help with both my topic here and for anyone reading this in the future.)

Again, I appreciate the help and hope I am not needlessly complicating this.

[NAZ]

[QUOTE=flip1216;417483]Naz/CraigS/GoDadGo - thanks for the quick replies and words of encouragement.

Naz - for clarification, we are attempting to get alignment *under load*, not while *at rest*? I ask because the only way to get the parallel alignment, as depicted in the picture you provided, *at rest* (how/when I would measure it) is to either have the transmission tail high (in relation to the crankshaft pulley/harmonic balancer) and the pinion 'nose' low (in relation to the back of the differential) ...OR to have the transmission tail low and the pinion 'nose' high. In my mind, if I don't do this, the angles will intersect, again *at rest*, instead of being parallel, thereby causing vibration. If the angles intersecting is okay *at rest* in order to accommodate a parallel alignment *under load*, I get that.

Flip, we set the static pinion angle at ride height and in relation to the trans output shaft. Our goal is that the trans output shaft and the pinion shaft are parallel under load during acceleration as any vibration will be magnified under load. If you watched the video of the leaf sprung drag car you noticed that the axle rotates more than three-degrees and this rotation needs to be accounted for during the static set-up. For a typical FFR three link suspension, the UCA link uses heim joints that do not flex but the LCAs have a poly bushing that does flex and will allow the rear axle to rotate some during acceleration. So, your static setting must accommodate the fact that under load your axle will rotate the opposite direction that your wheels turn – your pinion shaft and u-joint will tend to raise.

Most OEM front engine cars and truck have the engine mounted on a slope, typically a few degrees. If you drew an imaginary line through the crankshaft the front would be higher than the rear. And your trans output shaft will be on that same slope. That means that your pinion shaft will need to match that slope under load. Draw an imaginary line through the pinion shaft and under load it will be parallel to the imaginary extended centerline line through the crankshaft. These parallel lines do not have to be on the same plane and seldom are. And it doesn’t matter if your engine / trans slopes up in front or up in back – its just important that the pinion shaft extended centerline match that slope (angle) under load.

There is more to this alignment story but let that sink in first. One step at a time…

[Mark Eaton]

Flip, I think this is easier than you think. Here's what I did and after almost 2000 miles she runs great!

https://thefactoryfiveforum.com/showthread.php?25895-Eaton-s-Mk4-9130-Oregon-Build-quot-1000-Miles-quot&p=316955&viewfull=1#post316955

[flip1216]

Thanks again to everyone for the assistance and support as I learn through this process.

So I've measured the driveline using both the Spicer calculator (via a digital inclinometer) and the Tremec app. I followed Spicer's directions for determining if the slope was up or down (if the component starts higher at the front of the car than at the rear of the vehicle, it is down). I got the angle measurements from the same locations for both processes (the crankshaft pully, bottom of the driveshaft, and rear differential bolts). These are the results I got:

130658130659

What's confusing is that I think I'm in specs using the Spicer calculator (driveshaft less than 3* and operating angles 1 and 2 within 1* of each other). However, the Tremec app clearly shows I am not within tolerance...

[GoDadGo]

Flip,

All you need is a Cheepie Angle Finder to make short order of this issue.
Stick it on the front of the engine (Lower Pulley or Balancer) then stick it on the driveshaft mounting flange.
You just need to adjust it so that the driveshaft mounting flange is pointed downward by one to two degrees compared to your engine as your pre-load with the 3-Link rear.
The Cheepie Angle Finder lets you easily See The Angles Of The Dangle which I find a lot easier to understand since I'm a very visually geared guy.

Steve

Cheepie Angle Finder:
https://www.homedepot.com/p/Empire-Polycast-Magnetic-Protractor-36/100165800

[Big Blocker]

Think of your engine and rear end connecting together in a very flat "V" configuration. IF your engine is 2° DOWN at the rear (transmission yoke end) then your pinion needs to be 3° to 4° UP (meaning the pinion flange needs to be lower than the rear diff cover) to bring your angles to an acceptable 1° to 2° difference during acceleration. The confusion comes from numerous posts that describe the pinion angle as DOWN - that is incorrect. ALL measurements are taken from the drivers seat and from front to back - - - if the pinion shaft flange is lower than the rear of the diff housing, it is pointing UP.

Nuff said . . .

Doc

[NAZ]

Here's some more info on the subject you & others dealing with this subject may be interested in: https://www.therangerstation.com/tech_library/pinionangles.shtml

[GoDadGo]

Here's some more info on the subject you & others dealing with this subject may be interested in: https://www.therangerstation.com/tech_library/pinionangles.shtml

Angle Of The Dangle Explained Best By: The Naz