Driveline Angles-Data and 3 Questions

[BUDFIVE]

Builders, I need some advice on driveline angles. There’s Data then Three quick questions.
After dropping in the engine and transmission yesterday (build thread) I spent several hours today messing with driveline angles. Below are screenshots of an excel spreadsheet with my measurements of transmission angle, driveshaft angle, and pinion angle. The spreadsheet calculates ujoint operating angles and the overall working angle.
The second screenshot has my sketches of the angles for 4 shims, 4+ shims, and 4++ shims.
Measurement Notes, Results, and Questions:
Notes-
-All measurements work from rear to front, positive means slopes up.
-Pinion angle measured on flange and subtracted from 90 (90-89.5=+0.5)
-Transmission tailshaft measured on crank pulley and subtracted from 90
-Driveshaft measured on a 3/4” square tube across the driveshaft rear and front yokes (not slip shaft and flange yokes).
-spreadsheet cross checked against Spicer driveline calculator. The calculator shows all operating angles positive
-Trend digital angle finder in absolute mode, not zeroed since frame angle applies equally to all measurements.
-the IRS pinion angle is fixed at 0.5 up toward front.
-The shims are 1/4” transmission mount shims from Forte’s.
-Technique seemed repeatable with final measurement returning to 4 shims with same results.
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IMG_0984.jpeg

IMG_0982.jpegIMG_0981.jpegIMG_0978.jpeg

Results-
-with 3 shims (3/4”) the transmission tailshaft is below pinion flange center resulting in a negative driveshaft angle (slopes down from back to front). Operating angles exceed 3 deg.
-with 4 shims (1”) the transmission tailshaft is just above the pinion flange center and the driveshaft slopes up 0.25 deg from the pinion to the transmission. This results in a very small operating angle on the rear ujoint (-.25 deg). The front ujoint has a good operating angle of +2.15deg. Overall working angle is 1.9 deg.
Question 1–How worried should I be about this small operating angle(-0.25 deg)?
-with 5 shims (1.25”) the driveshaft angle gets steep enough that the rear ujoint angle exceeds 3 deg (3.9 deg). So I tried going back to 4 and adding one .090” washer (4+) and then two (4++).
-with 4+ shims (1.09”)the driveshaft angle is 1.6 deg up so the rear ujoint has OA = +1.1 deg and the front ujoint has OA=+.6. But they are both positive.
Question 2–both ujoint angles positive (same direction) is a no-no right?
-with 4++ shims (1.18”) the driveshaft angle increased to 3.2 deg resulting in rear ujoint OA +2.7deg and OA2=-1.2 and an overall working angle of 1.5 deg.
Question 3-if the small OA=-0.25 deg in Question 1 , and both angles Positive in Question 2 are a big deal, then I should make a 3/16” shim (.187”) and go with 4++, right?
Thanks for the help y’all. This ended up longer than I intended—I’m probably thinking too much again

[CraigS]

Your 4++ pic is my choice. 4+ a close second. In 4++ your trans and diff are just 1.6deg out of parallel which is near perfect. 4+ bumps that to 1.7. The overall goal is trans and diff parallel and w/ the irs there isn't enough room to get the driveshaft at too high an angle so I don't worry about that. For reference I always go back to solid axle setups where usually they want the diff pointed down at the front compared to the trans by 2.0deg. This was so that, on hard accel, when everything gives a bit, the diff nose would come up and be parallel to the trans. I have never thought about trying to measure this but my gut feeling is that the irs diff moves less than the solid axle diff. So anything <2deg difference between diff and trans is good to go. One other point. Since the 2015 irs came out it has been so common to use .750" to 1.0" shim that one could almost toss a coin and choose one or the other so you are in the company of many, many builders.

[Jeff Kleiner]

…This ended up longer than I intended—I’m probably thinking too much again

Attachment 199379



Jeff

[GoDadGo]

This video really will give you a real good understanding of what is happening with operating angles and U-Joint phasing.

https://youtu.be/Idk3BVDVHq4

Hope this helps simplify things for you because this stuff is Easy-Peasy once you see what is going on.

It is also why we want to always have the shallowest/minimal drive line angles that are possible.

Good Luck!

[BUDFIVE]

Attachment 199379



Jeff

Jeff, I can’t open the attachment and your PM mailbox is full. I don’t want to miss a good joke, especially on me.!

[BUDFIVE]

This video really will give you a real good understanding of what is happening with operating angles and U-Joint phasing.

https://youtu.be/Idk3BVDVHq4

Hope this helps simplify things for you because this stuff is Easy-Peasy once you see what is going on.

It is also why we want to always have the shallowest/minimal drive line angles that are possible.

Good Luck!

GoDad, good video. Takeaway is minimize overall working angle-the difference in opposing operating angle values on our 2 ujoints. Thanks

[GoDadGo]

GoDad, good video. Takeaway is minimize overall working angle-the difference in opposing operating angle values on our 2 ujoints. Thanks

Yep, it is just that simple so with that said:
/.You've Got This!

[BUDFIVE]

Folks, just to close this out-I did cut a shim from 3/16” aluminum and add it to the 4 shims from Forte’s. This is a total thickness of 1-3/16”. After reassembling, the angles (rear to front absolute) are: transmission 2.0 up, driveshaft 3.2 up, pinion 0.5 up, rear ujoint OA 2.7, front ujoint OA -1.2, overall working angle 1.5. Done.

But, for completeness, I’d still like to know the answer to question 2 above “ both ujoint angles positive (same direction) is a no-no right?”
If yes, With a short driveshaft, a very small change in transmission placement can put the driveline into bad alignment-lesson learned.

Thanks for the help

[Jeff Kleiner]

Folks, just to close this out-I did cut a shim from 3/16” aluminum and add it to the 4 shims from Forte’s. This is a total thickness of 1-3/16”. After reassembling, the angles (rear to front absolute) are: transmission 2.0 up, driveshaft 3.2 up, pinion 0.5 up, rear ujoint OA 2.7, front ujoint OA -1.2, overall working angle 1.5. Done.

But, for completeness, I’d still like to know the answer to question 2 above “ both ujoint angles positive (same direction) is a no-no right?”
If yes, With a short driveshaft, a very small change in transmission placement can put the driveline into bad alignment-lesson learned.

Thanks for the help

OK, the way I'm reading your description is that the front of the trans is uphill from the tail. And similarly the front of the pinion is uphill from the rear. Correct? If so this means that the nose of the pinion is 1.5 degrees down relative to the transmission output shaft. This is pretty much exactly what we strive for in a live axle configuration because under heavy acceleration the nose of the rear end will rotate upward, which in your scenario would bring it closer to the 2 degree angle of the trans output. It makes no difference whether both angles are positive, negative or if they cross through zero; I've said before that you can measure them with the car standing on it's nose and although the numbers may change the actual angular difference between output and the pinion doesn't! What's important is that relationship to one another and that as the front of the pinion rises during torque reaction it goes in the direction that makes it more parallel to the trans output. With all that though it's a moot point since you have IRS and the pinion angle will not change.

Jeff

[BUDFIVE]

OK, the way I'm reading your description is that the front of the trans is uphill from the tail. And similarly the front of the pinion is uphill from the rear. Correct? (Yes, correct) If so this means that the nose of the pinion is 1.5 degrees down relative to the transmission output shaft. This is pretty much exactly what we strive for in a live axle configuration because under heavy acceleration the nose of the rear end will rotate upward, which in your scenario would bring it closer to the 2 degree angle of the trans output. It makes no difference whether both angles are positive, negative or if they cross through zero; I've said before that you can measure them with the car standing on it's nose and although the numbers may change the actual angular difference between output and the pinion doesn't! What's important is that relationship to one another and that as the front of the pinion rises during torque reaction it goes in the direction that makes it more parallel to the trans output. With all that though it's a moot point since you have IRS and the pinion angle will not change.

Jeff

Jeff, yes you read my scenario right. And I understand your point on the pinion rising during torque with solid rear axles.
Where I got hung up with my question 2 was the other scenario (4+) with both ujoint operating angles in the same direction as they went from a pinion angle of 0.5 to a transmission angle of 2.2, 1.7 total-not as good as I ended up anyway. From your note, it doesn’t seem to matter if the angles are in the same direction.

Thank you

[rich grsc]

Transmission shaft and differential pinion shaft should be parallel, within 2-3*.

[BUDFIVE]

Rich, thanks. Yep I’m good at 1.5 deg from parallel.