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Vibes after re gear

Old 02-12-2019, 06:22 PM
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Default Vibes after re gear

So just had my Jeep re geared to 4.88. it's a 2000 with a hp30 and 8.25. Spartan locker in rear and just had a full case torsion style limited slip installed in the front. The jeep had some vibes but nothing too bad. Now, at 50 mph on the dot, I get a pretty bad vibration, like harmonic almost. All the way to 70 where I cap it. Removed front driveshaft, no change. Rear was an old front driveshaft I had cut and balanced years ago so I bought a brand new Adams for the rear. Still have the vibes, but under 40 is perfect now. Pinion angle is within 1.5 degrees in the rear. And just about 1 in the front. Rebalanced the rear tires, no change. Will do the front tomorrow but I'm running out of things to check .any suggestions?
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Old 02-12-2019, 07:23 PM
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Did you get any pictures of the backlash on the finished product? There is a break in period.
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Old 02-12-2019, 07:52 PM
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Yeah it's been about 1000 miles now, everything seemed fine when I changed fluid. Had some little sparkles but read that is normal for new gears. Nothing else seemed out of the ordinary/no weird wear on gears
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Old 02-12-2019, 07:54 PM
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Rotate the tires, see if it helps
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Old 02-12-2019, 08:06 PM
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I'll give that a shot tomorrow with balancing the front
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Old 02-13-2019, 03:27 PM
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Does this look too close to perfect pinion? After relooking I think I may be going positive degrees on the pinion when driving
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Old 02-13-2019, 03:55 PM
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You don't have perfect pinion angle. You are probably causing the vibration with that. The joints need to as close to the same angle on both ends of the shaft. Having one at say 7*, and the other at 1* is bad. Besides that, a u-joint actually needs to have some angle to it to properly lube itself. Take some shim out of the rear and try again.
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Old 02-13-2019, 04:57 PM
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^^^^ What he said. Your angle is perfect, if you were not running a SYE. But you are running one so that pinion needs to come down quite a bit

Do the opposite of what I say....

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Old 02-13-2019, 05:11 PM
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Gotchya. I've got 2 degree shims in there now, so I'll take them out
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Old 02-13-2019, 06:10 PM
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Originally Posted by 5-Speed View Post
^^^^ What he said. Your angle is perfect, if you were not running a SYE. But you are running one so that pinion needs to come down quite a bit
I thought if you had the stock driveshaft you want the pinion parallel to the transfer case output so the u-joints will be at the same angle, and if you have an SYE with a double cardan shaft you want the pinion to be pointing at the output yoke?
https://www.quadratec.com/jeep_knowl.../article-3.htm
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Old 02-13-2019, 06:18 PM
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Read post three in this thread.

https://www.cherokeeforum.com/f2/dri...37/#post398646


Ideally, the operating angles on each end of the driveshaft should be equal to or within 1 degree of each other, have a 3 degree maximum operating angle and have at least 1/2 of a degree continuous operating angle.

The reason for this is because a cardan joint is not a homokinetic mechanism, this means that they produce uneven shaft speeds when operated at joint angles of more than a few degrees, and to correct this rotating speed variation the yokes on the main shaft are disposed with an offset angle of 90, so that the accelerating and decelerating phases are canceled.

A double cardan joint, despite not being a constant velocity joint, is a good approximation of it, and can manage joint angles up to 5-6 degree in continuous operation.



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Old 02-13-2019, 06:26 PM
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Whoops.... I will edit my post.

Ya its been a while since I set one up. Here is what mine looked like for reference. Comparing the 2, you have a lot of exposed spline on yours. My first shaft had about the same and it had vibes. I had Adams redo it a bit longer and the vibes were gone after.


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Old 02-14-2019, 05:33 AM
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The vibes were there before the driveshaft so I don't think that is it . Although I will email Adams about the splines. As for my pinion, ideally you want it pointed at the tcase but a degree or two below to account for axle wrap, which I don't think I have. I'm taking the shims out today and will report If it helped
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Old 02-14-2019, 06:31 AM
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My guess is to much positive pinion angle. You had it before the regear and when you went to 4.88 to gave more torque to the rear axle. This also gave you a little more axle wrap and highlighted an existing problem.
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Old 02-14-2019, 07:21 AM
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That's my guess too. Before I got vibes but around 75+ but I never went that fast. Now it's showing it's ugly head around 50 cause the new driveshaft speed .
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