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Old 11-26-2010, 11:19 PM
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Another vibe thread...sorry, please help

I have a 94 YJ and recently went to a RC 2.5 lift when my factory springs finally gave out. I have BAD vibes now but not at the speed I would have expected it. It is terrible taking off in 1st and then early on in 2nd and tapers off in 3rd. There is a slight vibration in higher gears but it actually smooths out the faster I go eventually getting smooth after 60mph. The kit didn't come with a TC drop and RC as well as my local shop said I didn't need one with a 2.5. The rear springs come with slims installed and I thought that was great as I put it on as I watched how in rolled the pinion angle upward. Now after the vibes, I search and found graphics on Tom Woods' site that said the pinion should be on the same plane as the TC output for the conventional, 2 joint shaft. My pinion is definitely rolled upward and not parallel to the output. The CV shaft diagram on Woods' shows the pinion rolled up and parallel to the driveshaft. Could it be that I don't need the shims on the springs and therefore roll the pinion angle back down closer to plane of the output on the TC? I have a BD 3.5 on an 84 CJ and there aren't any shims there; no vibes either. I need to head to camp Sunday and need to be vibe free. Thanks in advance!
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Old 12-05-2010, 08:37 AM   #2
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I'm fairly new to the Jeep world, (95 with 2.5 ltr), and I am in the same situation that you're in. I chose the RC because of cost, and the install seemed to go fine until I drove it. Vibes were very bad and RC customer service told me the same thing, that it didn't need any sort of TC drop. I ended up spacing the TC 1 1/4 inches, but it looks terrible and there is still a bit of vibration from 25 to 35 and a slight bit going through 45 mph, but it is driveable.
RC has been very consistent telling me that the 2.5 inch lift on the YJ requires nothing in the way of modifications and that I should not have any vibes.
I've decided not to compromise and am in the process of installing a JB SYE and will be ordering a new driveshaft this week. FWIW, JB was not surprised that I was experiencing vibes at just 2.5 inches.
Personally, I think any sort of lift project should be looked at with an SYE in mind. It just makes little sense to raise a Jeep only to lower portions of it to make it driveable.

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Old 12-05-2010, 08:51 AM   #3
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have a stock '04 sport (except tires) it has been "eating u-joints" I don't know if bad batch cheap or what. The shop I am using is nationally known and using Napa parts-but the "Vibes" have been the sign every time. Replaced stock set about 8 months ago-replacements went "bad" about 3 weeks ago. Road trip Wisconsin last week-this new set shot. Will all be replaced for free again-but a bit of a pain. Point is have the u-joints been checked-even if new?
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Old 12-05-2010, 08:40 PM   #4
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You are correct that the the pinion and output shaft should be parallel. That being said, I was running a 4" RC lift with shims and a TC drop and my pinion seemed higher than is recommended and it ran fine with no vibes.
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