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Old 04-17-2015, 08:53 PM
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Default Learned something new on drive angles

Getting my 40 just right, I wanted to dial in the drive angles. There was a small vibration when I drive 70. I know, most of you 40 owners don't have that problem

Talking to Robbie, he mentioned Tcase and rear diff angles need to be just right or it will vibrate.

Using a$5 Harbor freight angle measurer, my Tcase was pointing up 2 deg, the rear Diff was pointing up 6 deg. I needed to get the rear down about 4-6 deg to make them operate better.

I ordered 4 deg shims from Georg at Valley Hybrids and installed them in less than an hour. Will test it tomorrow to see how it handles.

I am sure I had this issue with my last 40, just never knew to look

1st file is the Tcase,

2nd is the rear diff, have to know where 90 is to see it is pointing up 6 deg

Last photo is after I installed the 4 deg shims

It's always nice to learn something new that's easy to do yourself
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Old 04-17-2015, 09:11 PM
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This is one of the better videos on the subject:
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Old 04-17-2015, 09:21 PM
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That's awesome. Took me a while to understand. That makes it simple
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Old 04-18-2015, 05:59 AM
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It's worth the time and effort to get this figured out. I did the measurements on my old 40 and had custom steel shims made. It drove smooth on the highway, even with the 2F, swampers and manual steering.
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Old 04-18-2015, 06:19 AM
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Quote:
Originally Posted by Romer View Post

I am sure I had this issue with my last 40, just never knew to look
Yeah, but nothing a lowering kit couldn't fix..


sweet stuff, love the video! thanks for sharing
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Old 04-18-2015, 09:06 PM
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Cool video
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Old 04-18-2015, 10:29 PM
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Driveshafts obey physics

Angular velocity was hard for me to grasp in school, until my dynamics professor explained it using driveshafts. That was something I could get!

Ujoints, as you found out Ken, require equal (or nearly) and opposite angles to operate properly: The change in angles cancel and angular velocity is conserved in the system.

A nice mod for older trucks is to go to a double cardan, or constant velocity joint, at the tcase end. As the name suggests, these joints conserve angular velocity through the joint: they don't have the oblong motion you saw in the video.

This allows the pinion to be rotated up, out of the way of rocks, as the single ujoint end must now have zero angle so it also has no change in angular velocity. Birfields, Rzeppa, and tripod joints also conserve angular velocity: also called CV joints.

This is usually done on the rear, as the front often requires a cut and turn to maintain the proper castor in the front. Anyway, a thought if you end up beating your driveshafts and pinion's on rocks.

If you require more boring, dorky, pedantic blather on the subject, I'm happy to oblige LOL
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Old 04-18-2015, 11:17 PM
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Yeppers, you always want the pinion and t-case output to be parallel with regular u-joints. It always pains me when I see diffs pointed up toward the t-case with regular u-joints. In my Solidworks class, one of the things we did was design and simulate u-joints. It's just one of those physics/geometry things. Now, if somebody would school us on orbital mechanics, now that would would be cool too!
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Old 04-18-2015, 11:19 PM
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Quote:
Originally Posted by Romer View Post
I know, most of you 40 owners don't have that problem
True, usually I am going 85 MPH with 7 men inside!
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Old 04-19-2015, 12:34 AM
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Quote:
Originally Posted by AxleIke View Post
, pedantic
Damn finally a word in there I understood!!
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