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Old 08-19-2014, 11:17 PM   #1
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i got a vibration at speeds 35 to 55.

I had some friends sitting in the back and I didn't have the vibration but without the weight it does it between those speeds. Someone told be to put wedges under rear axle due to the angle into rear end. I have already replaced motor mounts and transmission mount that I found was busted. If this don't work any advice.

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Old 08-19-2014, 11:30 PM   #2
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Transfer case drop is easier than the wedges on the leaf springs. Their correct name is a degree shim. If it has a lift kit on it, the rear springs should of came with the degree shims already mounted on them. At least most of the lift springs have them.

If you want to do the degree shims, then you have to take the u-bolts off, lift the rear up and out of the way. Take the center pins out of the leaf spring pack, and replace with new as well as the degree shim mounted on the top. Then re-install all of the other parts that were dismantled in the process. The degree shims come in anywhere from 3* to 7* depending on the amount of lift that is on the Jeep. Most popular is the 6* shims.

Sometimes it requires the t-case drop even after you install the shims. Depends on the amount of lift.

If that doesn't work (like it didn't on mine) then what is needed is a slip yoke eliminator kit and a CV driveshaft. Then the vibes will be gone. Along with the T-case drop.

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Old 08-22-2014, 12:37 PM   #3
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Thank you for the info on the transfer case drop. I'm new to jeeps and have never heard of that before. I will check that out. The vibration is driving me nuts. It does it when you giving it gas at those speeds and quits when I left off the gas and rides smooth. Just don't understand.
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Old 08-22-2014, 01:36 PM   #4
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What you are experiencing is axle wrap under load, which can be a problem if the driveline angles aren't set to properly compensate for it. All it takes is being just a few degrees off to get vibes.

Check your driveline angles.

Based on your description that passenger weight in the rear eliminated the vibes, chances are that a small t-case drop will fix the problem. Some folks stack washers in a trial and error fashion until they find the precise amount of drop they need to eliminate the vibes.
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Old 08-22-2014, 05:57 PM   #5
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I'm pretty new to jeeps as well but have had to learn a whole lot quickly. How much lift do you have? I had vibes similar to how your describing. Mine ended up being worn u-joints in my front axle shaft and a rear driveshaft that was out of balance.
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Old 08-22-2014, 08:05 PM   #6
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It might be worth mentioning if this recently started and you have had the lift for a while, that your driveshaft angles may have taken out your u-joints as well.

transfer case drop is pretty easy, you can back all the bolts out 3/4" then pull the bolts one at a time to install the spacers, with a breaker bar or an impact gun, you are probably going to have less than 30 mins. into the job.
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Old 08-22-2014, 11:47 PM   #7
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I took it to a drive shaft shop and he looked and said I needed the 6 degree wedges and sent me to get some. I hadn't installed yet. I hadn't had a chance to check on the transfer case drop yet. My wife found a shop that deals with jeeps and going get with him and see about the transfer case drop.
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Old 08-23-2014, 12:06 AM   #8
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It only has a two inch leaf spring put in it before I got it but I have found other things out that was did and not actually done right.
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Old 08-23-2014, 08:41 AM   #9
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shake rattle and roll

i got an 87 also, mine keeps dropping u-joints out of the pinion yoke, i have wedges, and i just recently installed 1" lowering blocks, and can't use the SYE, cause i don't have the Np231... i've lost 3 u-joints in the last year, any other ideas what might be causing this...?
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Old 08-23-2014, 12:54 PM   #10
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Quote:
Originally Posted by panman63 View Post
i got an 87 also, mine keeps dropping u-joints out of the pinion yoke, i have wedges, and i just recently installed 1" lowering blocks, and can't use the SYE, cause i don't have the Np231... i've lost 3 u-joints in the last year, any other ideas what might be causing this...?
U-joints wear out faster when the operational angles exceed the recommended specs.

First, you need to measure the driveline angles and adjust them as needed by either changing the shims or doing a t-case drop, or doing both. A 1" t-case drop may be too much, or not enough. The shims you have may not be the right ones. You also need to make sure you compensate the rear pinion angle to account for normal axle wrap under part cruise throttle. Usually 1* is all that is needed to compensate for axle wrap for springs in good condition. Unless you measure the angles, you are simply working blind and guessing as to what you need to do and how much to do it.

If the angles are good but you still get vibes and are losing u-joints, you need to make sure you aren't getting too much axle wrap itself. Even if you set it up by the book, too much wrap can throw the angles out of spec when you mash the gas pedal, and as a result it can wear the u-joints out fast. You also need to make sure the driveshaft angle isn't too steep as that will affect operational angles.

As far as SYE's go, I think I remember hearing about a hack-n-tap style SYE for the early YJ's that don't have the NP231. Don't recall who makes the kit though.
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Old 08-23-2014, 09:00 PM   #11
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How will I know if the u joints are bad. I have grabbed the drive shaft and it doesn't have any play in them. But I never had a jeep before so I'm learning as I go.
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Old 08-25-2014, 08:11 PM   #12
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Play in the u-joint is usually the indication of a bad u-joint. Other than that, the only way I think you can tell if the wear is excessive is to take the u-joint apart, pull the bearing caps, and look at the needle bearings. Most people just go by play in the u-joint.
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Old 08-25-2014, 09:43 PM   #13
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Sometimes you have to take the straps off and see how it feels. My front DS was solid when attached, but when undone it did not spin smoothly, there was a definite clicking when moved around by hand.
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Old 08-27-2014, 12:19 AM   #14
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Well I took the transmission mount back out and moved the preload spacer under the mount and replaced every thing. Now the vibration is between 40 to 50 now. I'm going replace the transmission stabilizer to see if that helps since I tighten it up that day and it started the vibration thing. I'm still going but wedges in I think just in case I add some more lift later.
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Old 09-01-2014, 08:33 PM   #15
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Well I'm not real knowledgeable on 4x4 and when everybody said to do a transfer case drop my mind was not thinking what Yal was meaning to do and now I realize what Yal was talking about and will be so much easier to do. I will do that the next time I'm off. I had to work on my sons truck the last time to get him running again.
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Old 09-05-2014, 12:35 PM   #16
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I want to thank you all for all the advice. I finally got under there and dropped the transfer case and it worked. It rides so smooth now. Thank you all again for the help.

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