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  #21  
Old October 26th, 2015, 09:20 PM
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Well, so I've checked a few things:

1. Rear ball joint came with the truck, but seems to be in good condition. Or at least in unknown condition. No noticeable play, but I will check again when I remove the rear a-frame for painting.

2. Trans mounts appear fine, no movement prying against the transfer case.

3. Left rear orange poly bush is disintegrating. Not sure why just that poly bush, but it's starting to crumble. Not sure what effect that has on driveshaft vibration.

4. Rear driveshaft u-joints are not in phase. This is a huge surprise. When did this happen? Are the rear driveshaft u-joints supposed to be in phase? I thought only the front is supposed to be out of phase due to the pinion angle.

Is it possible that my vibes are due to the rear driveshaft being out of phase?
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  #22  
Old October 27th, 2015, 07:28 AM
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  #23  
Old October 27th, 2015, 07:38 AM
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Yes the rear should be in phase.
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  #24  
Old October 27th, 2015, 07:43 AM
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OK. I'll fix this and the trailing arm bushing, point the pinion down to 0~1 degree and report back.


but uh....I need to figure out how the rear driveshaft got out of phase in the first place. I'm looking back through some old photos now to see if they have always been out of phase or if somehow they spontaneously got out of phase.
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  #25  
Old October 27th, 2015, 08:05 AM
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If it is out of phase someone disassembled it and reassembled it incorrectly. That just doesn't 'happen'. Maybe to install a rubber dust shield? That wouldn't happen at a driveline shop. It must be in phase...
The damaged poly bush will cause vibration issues too but it won't likely be speed correlated.
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  #26  
Old October 27th, 2015, 09:24 AM
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Yeah...it looks like I screwed it up somehow. As usual I am the one to blame
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  #27  
Old October 27th, 2015, 11:03 AM
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2" lift versus ???

You will get it sorted mate. Keep at it. Weird about the polybush though. Have you had the suspension at full flex yet and noticed any abnormalities in the bushings?
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  #28  
Old October 30th, 2015, 10:27 AM
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Thanks Jonesy

1. So, I rotated my pinion down to 1 degree from horizontal. Not difficult - just added about 3/8" in spacers to the RTE rear arms.

2. I changed out the bad bushing.

3. I completely disassembled the A-frame from my truck for powdercoating and found the following:

a. The a-frame ball joint has a tiny little bit of play. I have ordered a new one.
b. The a-frame ball joint runs out of articulation when the suspension drops by an inch. I'm not sure if this is really a problem, but it is kind of odd. Has anyone run into this? Do they use a limit strap? Or do they just let the ball joint itself stop the suspension from dropping?

Going to fix the driveshaft issue next.
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  #29  
Old October 30th, 2015, 02:00 PM
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Rear A-frame max balljoint articulation is 36 degrees.

Length of A-frame from between points of articulation is approximately 27".

Therefore, the maximum vertical travel of the A-frame is = 2*r*sin(theta/2) or:

2 * 27" * sin (36 degrees / 2) = 16.678"

Which means that if I am maxing out the articulation of my balljoint, then I am literally at the bottom of its travel. This means that the resting angle of the balljoint must be modified to allow maximum compression, but with say a safety factory of 1 inch, but no more.

The measured distance from the bump stops on my axle to the rubber bump stops is...
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  #30  
Old October 30th, 2015, 02:07 PM
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Quote:
Originally Posted by sonoronos View Post
Rear A-frame max balljoint articulation is 36 degrees.

Length of A-frame from between points of articulation is approximately 27".

Therefore, the maximum vertical travel of the A-frame is = 2*r*sin(theta/2) or:

2 * 27" * sin (36 degrees / 2) = 16.678"

Which means that if I am maxing out the articulation of my balljoint, then I am literally at the bottom of its travel. This means that the resting angle of the balljoint must be modified to allow maximum compression, but with say a safety factory of 1 inch, but no more.

The measured distance from the bump stops on my axle to the rubber bump stops is...
Well we have a 45 degree ball joint...add that to your equation
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  #31  
Old October 30th, 2015, 02:13 PM
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Quote:
Originally Posted by Z.G View Post
Well we have a 45 degree ball joint...add that to your equation
Good call Zack...but it's rather expensive right? I mean, the aftermarket ball joint is interesting, but I'd like to keep costs down by using stock consumables and modifying only those components that are non-consumable
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  #32  
Old October 30th, 2015, 02:15 PM
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How much lift are you sitting at? It must be a lot. Have you changed the shock mounts to allow for extension travel?
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  #33  
Old October 30th, 2015, 02:36 PM
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Quote:
Originally Posted by Red90 View Post
How much lift are you sitting at? It must be a lot. Have you changed the shock mounts to allow for extension travel?
About 3.5" or so. Maybe 4"? It's difficult to tell and varies with load. The shock mounts are Rockware rear hoops with RS5012's.
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  #34  
Old October 30th, 2015, 02:39 PM
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Quote:
Originally Posted by sonoronos View Post
Good call Zack...but it's rather expensive right? I mean, the aftermarket ball joint is interesting, but I'd like to keep costs down by using stock consumables and modifying only those components that are non-consumable
Definitely pricey...only reason I haven't thrown it in my truck yet. Otherwise, it's greasable so it's nice to have a serviceable ball joint there.
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  #35  
Old October 30th, 2015, 02:42 PM
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4" and you are wondering about driveshaft vibes..... Yah, all your geometry is a mess at that kind of lift and you really need to correct everything.
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  #36  
Old October 30th, 2015, 02:44 PM
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  #37  
Old October 30th, 2015, 05:04 PM
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Yes, this hell I am in is self-inflicted

I'm guessing there isn't much literature about this on the web since few people actually do this sort of thing. Hopefully, this thread's information will be useful.
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  #38  
Old October 30th, 2015, 05:15 PM
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OK. to continue, the distance from the axle perch to the bump stop is currently 8" on jackstands at max ball joint articulation, 7" when resting on the ground.

Adding 1" for safety. That means I need to modify the angle of the ball joint to allow for 7.678" of downward travel.

d = 2*r*sin(theta/2), therefore:

2*arcsin(d/(2r)) = theta

2*arcsin(7.678/(2*27)) = 0.285 radians or 16.348 degrees.
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  #39  
Old October 30th, 2015, 05:46 PM
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Things smooth out over 8". That is your problem.
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  #40  
Old October 30th, 2015, 09:50 PM
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Ed you are one of the smartest dudes I know. And I believe you will one day probably figure it out. I mean there are monster trucks out there right!

But still. ..... Easy fix = drop your lift to 2"
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