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SYE install degree shim calculations

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Old 02-08-2013, 12:29 AM
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Default SYE install degree shim calculations

I know this has been talked about but my numbers seems way different than others are getting.

1994 2dr sport, AX15 (5-speed), C8.25 axle, 4.5" RC lift yielding 6" measured at the rear axle.

This is a full pack spring lift with stock shackles.

Pinion angle measures 3.6 degrees.

Drive shaft fitted into place measures 19.6 degrees.

So I need to reduce the angle by 19.6 - 3.6 = 16 degrees.

Drive shaft length is ~3x the pinion length so every degree I rotate the axle should raise the drive shaft end enough to reduce that drive shaft angle by ~1/3 degree.


16 / 1.33 = 12 degree required shim.

The biggest shims I see are on the market are 8 degrees.

These would improve my angle by 8 * 1.33 or about 11 degrees leaving me about 5 degrees out.

Is this reasonable?
Old 02-08-2013, 12:42 AM
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Take a pic for us. Throw a 4 degree in there, and take another pic. Most are fine with 1 degree pinion low.
Old 02-08-2013, 01:00 AM
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I really don't think 4 degrees is going to do it.
Attached Thumbnails SYE install degree shim calculations-driveshaft.jpg  
Old 02-08-2013, 01:25 AM
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One question have ya drove it since sye instal ?
Old 02-08-2013, 01:59 AM
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Originally Posted by freegdr
One question have ya drove it since sye instal ?
No. I need to do some brake work before I would even consider it.
Old 02-11-2013, 10:47 AM
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Originally Posted by freegdr
One question have ya drove it since sye instal ?
May I ask the significance of this question?

Will it change when driven? I don't see why it would.
Old 02-11-2013, 11:02 AM
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Default shim

if you run a slip yoke elimantor on it you technically wont need a shim but if u decideto u should look around 3 degrees
Old 02-11-2013, 11:26 AM
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Originally Posted by sreeb
May I ask the significance of this question?

Will it change when driven? I don't see why it would.
Driving can cause the suspension to settle a bit and may improve the angle. I put shackles in the rear and it was a 1/2" higher when i put it on the ground before driving a lil.

Originally Posted by Baby D
if you run a slip yoke elimantor on it you technically wont need a shim but if u decideto u should look around 3 degrees
Not true. if the U-joint on the axle end is out of alignment with the DS then you will get vibration and shorten the life of the u-joint.
Old 02-11-2013, 01:10 PM
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Originally Posted by No4x4Yet
Driving can cause the suspension to settle a bit and may improve the angle. I put shackles in the rear and it was a 1/2" higher when i put it on the ground before driving a lil.



Not true. if the U-joint on the axle end is out of alignment with the DS then you will get vibration and shorten the life of the u-joint.
The suspension was installed by the previous owner along with a transfer case drop. It doesn't have many miles on it but it isn't new either.

I just removed the transfer case drop and installed the sye.

I have the factory shackles. Longer shackles would improve the pinion angle.
Old 02-11-2013, 01:19 PM
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Originally Posted by sreeb
The suspension was installed by the previous owner along with a transfer case drop. It doesn't have many miles on it but it isn't new either.

I just removed the transfer case drop and installed the sye.

I have the factory shackles. Longer shackles would improve the pinion angle.
Did you put the jeep on stands at all? I was saying that anytime, new or old when you take the weight off the jeep the suspension can take a few miles to settle back to normal ride height.
Old 02-11-2013, 01:56 PM
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Originally Posted by No4x4Yet
Did you put the jeep on stands at all? I was saying that anytime, new or old when you take the weight off the jeep the suspension can take a few miles to settle back to normal ride height.
No. I just drove it over the service pit.

It is at "normal" ride height.

I plan on doing some work on the rear suspension to fix the shackle angles and hopefully lower it a bit but for now, it is what it is.
Old 02-12-2013, 09:34 AM
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Originally Posted by sreeb
Pinion angle measures 3.6 degrees.

Drive shaft fitted into place measures 19.6 degrees.
Is either of these numbers in line with what other people are seeing before adding shims or is one of them way out?
Old 02-12-2013, 10:35 AM
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are you supposed to measure the degree that your ds is slanted from perfectly horizontal to find out what degree of shim you need or am i completely wrong??..
Old 02-12-2013, 10:54 AM
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I don't think you are measuring the pinion angle properly....

the best way to do it is to stick a degree finder underneath the yolk or on a flat spot of the pumpkin. basically you want the rear axle to point straight up with the driveshaft towards the transfer case. 4 degree shim would probably be fine
Old 02-12-2013, 11:01 AM
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I have 6 degree Shims.
Attached Thumbnails SYE install degree shim calculations-forumrunner_20130212_120115.jpg  


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