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Pinion Angle

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CamJam View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CamJam Quote  Post ReplyReply Direct Link To This Post Posted: Dec/13/2018 at 10:14pm
U-joint operating angles should be no more than 3 degrees and within 1 degree of each other, so you're there already.  The problem may be, as previously mentioned, that torque will force the pinion higher under acceleration.  I'd be inclined to go with what you have first and see how it works, especially as new springs will settle with time.  You can always add a wedge to each leaf later if you need to.

U-joint manufacturers recommend a minimum u-joint angle of 1 degree for proper lubrication, but you're close enough that I wouldn't worry about that too much.

Keep in mind that as you point the pinion down, you will increase the driveshaft angle, and you can quickly exceed the recommended 3 degree maximum u-joint angles. It can become a bit of a push-me-pull you.  This isn't a big problem with an AMX driveshaft, but with a short driveshaft (like the 13" one I have on my Opel GT) it had me chasing my tail at times.

Here's a great calculator that might help you, especially if you have to add wedges later.  If you follow the 3 degree max (and within 1 degree of each other) rule mentioned above, you shouldn't have any driveline related vibration problems unless you have a bad u-joint.


It's not absolutely necessary to have the car on level ground, as you're only interested in the relationship of the U-joint angles to each other, but it does make calculating easier and assures that you're not compressing the springs at either end of the car while you're measuring.

I usually measure angles with my weight (160 lbs) in the driver's seat and the spare tire and jack in the trunk.  



Edited by CamJam - Dec/13/2018 at 11:09pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Someassemblyrqd Quote  Post ReplyReply Direct Link To This Post Posted: Dec/13/2018 at 11:08pm
cam - thanks for the url.  I h@ve this site.  Very useful.  When I plugged my data in, it confirmed what I suspected.  My rear pinion angle was over 176* with the rear axle yoke facing upward, which is a negative angle. Remember math, any number minus a negative number gives you a positive value.  I should go back and correct my original post calc for the rear angle. It even took me several times to remember my math.

My reverse calculations indicate I need 6* degrees to shift the pinion to a positive value.  More to come.

Greg
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CamJam Quote  Post ReplyReply Direct Link To This Post Posted: Dec/13/2018 at 11:39pm
Greg... 6 degrees sounds like a huge amount for wedges.  Unless I'm misunderstanding you, it sounds like you have the pinion reading backwards.  If the pinion is pointing up towards the front of the car, this is considered a down slope for the purposes of the calculator.  If the front is higher than the rear it is a down slope.  Your transmission, driveshaft and pinion were all down slopes, so your original post sounds more like what I would expect.
.
The program notes for the Spicer calculator say it best: "CAUTION: Most axles have an end yoke that points UP,  but since the rear of the axle is usually lower than the front of the axle, it is, for the purpose of this program,  a DOWN slope."


Edited by CamJam - Dec/14/2018 at 1:05am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PHAT69AMX Quote  Post ReplyReply Direct Link To This Post Posted: Dec/15/2018 at 2:26pm
For sake of discussion, if existing Pinion is 3 Degree "up" and 6 degree leaf spring shims are used, then Pinion would be moved to 3 degrees "down", so angle would still be "equal" to the opposite end, just on "the other side" of the Driveshaft Centerline, would it not ?

What information I failed to "keep" is:
? Is the Trans Tail higher or lower in elevation than the Rear Differential Pinion ?
? Which way is the Drive Shaft Slopped from Front to Back ?

IF the Trans Tail is angled down and Lower than the Diff Pinion
Then the Drive Shaft will be slopping UP at the Rear.
This arrangement will cause the Pinion U-Joint Angle to Increase
when the rear housing twists under load which is "not good", right ?
With 6 deg shims in the Rear, BOTH the Trans Tail and Pinion would be 3 degrees down...
Just for discussion, so they would still be Equal U-Joint Angles at both ends, right ? 




Edited by PHAT69AMX - Dec/15/2018 at 2:30pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Dec/15/2018 at 2:48pm
being for simplicity, angling the tranny tail shaft down is a 4x4 or heavy equipment thing, as the bigger rear lift needs the propeller shaft angled down, while the pinion is angled up.

For cars driven on the streets, the rear would drop slightly under load, but can drop significantly when over loaded. Angling the pinion up under that condition would cause angle at the pinion to increase beyond the set angle, more often than not.

A slight downward angle is to compensate for rear drop under load or hard launches. Which Is good to keep premature breakage from binding or premature failure.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mopar_guy Quote  Post ReplyReply Direct Link To This Post Posted: Dec/15/2018 at 10:40pm
After re-reading his post, I think his angles are fine and don't need changed if it was measured right. But due to his explanation I'm not sure that he's taking the measurements properly. Here's another good read.

Here's mine I just took a week ago. The rear operating angle is usually closer to 1° but the car had been on the lift for over a month letting the springs relax. It's not a drag car so having the pinion point down is a moot point for me. There's so much BS on the internet about pinion angles it's not even funny. I've had a couple of good shops tell me these angles are fine for a street car and it runs smooth going down the road. I learned a lot about this stuff after putting the 8.8 in it without shortening the left side to center the pinion. What a headache that was! So when I changed out the entire driveline this year I wanted it perfect and this was as close as I could get it and it works.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Dec/16/2018 at 6:44am
In a perfect world, the transmission and pinion angles would be the same and the offset height will give you the drive line angle.
That stated, the angles side to side are also to be within tolerance.
AMC engines are typically 1" to 1-1/2" mounted towards the passenger side as with most left hand drive vehicles until rack and pinion steering came along and they started centering the engine/transmission.
 On the 8.8 offset differential, what angle did you finally end up with and did you have to move the transmission rear mount?
The reason I ask is I've made several 8.8's for AMC's and have always centered the pumpkin to achieve side angle as well.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mopar_guy Quote  Post ReplyReply Direct Link To This Post Posted: Dec/16/2018 at 9:10am
With the offset pinion you get what's called a compound angle which is taking the offset, dividing it by 2 and adding those numbers to each ends angle. That drives those numbers up fast! I started out with over 4° on each end so I raised the trans up as far as I could get it, changed the pinion end to match it and ended up about 3.2° on each end. It still had the oscillating vibration at certain speeds but it was tolerable. Over 80 mph and it got pretty bad when the shaft speed got over 3000 rpm. One thing I found out with that is how matching the joint angles mattered. Even a half degree difference made the vibration worse. Putting extra weight in the trunk made it change.
That's another line of BS on the internet about how an offset pinion doesn't matter. Ouch At least I got what I had in the rear end back as they're popular with the Jeep guys. The 8.8 is stronger than the Dana 35.

"Hemilina" My 1973, 5.7 Hemi swapped Javelin
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Someassemblyrqd Quote  Post ReplyReply Direct Link To This Post Posted: Dec/16/2018 at 12:55pm
 Mopar, Phat, 304 - so for my knowledge and accuracy of discussion, in the above first diagram, the pinion is “down”⬇️ and in the second, the pinion is “up”⬆️ and is consistent with the down or up reference in the spicer parts.com url for calculating tranny/pinion angle? 

I get my driveline back from balance in Monday.  I will level my AMX, measure floor to shaft height to verify the pinion height is lower than tranny spline, and then remeasure tranny, driveshift and pinion angles .   

I’ll let you know the final results and what my plan of action is.

Your insight and knowledge is greatlay appreciated.  Thx. Greg
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tufcj Quote  Post ReplyReply Direct Link To This Post Posted: Dec/16/2018 at 1:39pm
Originally posted by PHAT69AMX PHAT69AMX wrote:




In the 4x4 world, we always tried for what's shown in the lower pic.  Draw a line parallel to the trans tailshaft and another parallel to the pinion.  These 2 lines should be parallel.  On 4x4s we generally set the pinion about 1-2 degrees low to compensate for it rotating upward under power.

You could have a shaft built with a CV front joint, then rotate the rear so it is about 1 degree or less from parallel with the driveshaft.

Bob
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