Does the output yoke on your SYE move at all? -
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post #1 of 4 Old 10-01-2013, 06:42 PM Thread Starter
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1993 YJ Wrangler 
Join Date: Oct 2012
Location: Kodiak
Posts: 120
Does the output yoke on your SYE move at all?

Ive been chasing a horrible vibration problem. It happens above 40, is speed, not gear or engine speed related, gets more intense under acceleration, and the worst on deceleration, esp. after heavy acceleration.

Eventually found out that my driveshaft splines were completely frozen. I had to use a pry bar to get the flange off of the pinion to remove the "old" shaft. Anyway, I had just lived with this vibration for a while. While I was putting my shiny new tom woods on, I noticed the rear output yoke on my np231 was able to move about 1/8th inch forward and back, but the nut was tight. The entire output shaft was moving. I dont remember that being the case when I put the SYE in. Does anyone know if thats a normal thing on their SYE?

Oh if it helps, I noticed it first after an axle, motor and transmission swap. I blew up my 35 and broke U joints in one "rear end anit-gravity event". Decided to go all out. The 8.8 was "new" from ecgs, and the 4l60e new from novak, so im sort of guessing that they arent the problem. The pinion is aimed properly, Driveshaft is a double cardan to accompany the lift...I cant think of anything else it could be. Yall think I need to tear apart the 231?

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post #2 of 4 Old 10-01-2013, 08:58 PM
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1992 YJ Wrangler 
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Location: Neosho
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I have no idea about the in/out play, but are you sure that your your output shaft isn't bent? Currently, I have a similar vibration from a slightly bent axle shaft. Mine has no symptoms until exactly 64 mph.

The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed. ― Robert M. Pirsig, Zen And The Art Of Motorcycle Maintenance: An Inquiry Into Values
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post #3 of 4 Old 10-01-2013, 10:29 PM
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1989 YJ Wrangler 
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It shouldn't move front to back. Doubt that would cause vibrations just a leak. Maybe throw it in gear without the driveshaft to check if it's spinning smooth. (not bent) I bet your frozen splines have something to do with the slop seen in the output shaft.

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post #4 of 4 Old 10-02-2013, 11:15 AM
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I would look into your t-case. The yoke should not be able to move that much. I think that could potentially cause some of your vibrations. If that yoke slides on the output shaft while driving, it could hit a harmonic frequency and amplify minor vibrations.

Have you removed the front DS to isolate the problem to the rear? I would do that first. If the problem persists, I think taking a look at that t-case could be in order.

As rambo stated, you should also check to be sure the output shaft is true as well. Your vibrations may be caused by multiple factors. I don't know if the sole problem is the yoke, but i definitely would check it out.
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