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Old 02-05-2014, 07:15 PM   #1
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Slip Yoke Eliminator/Lift Kit

I have a 1989 Jeep Wrangler Sahara and I am installing a 4 inch rough country lift kit. Do I need to install a slip yoke eliminator? and if I do need a slip yoke eliminator do I still need to install the transmission/transfer case skid plate shims? I am new to owning a jeep and Im trying to do most of the work myself so I can call it my jeep and that I built it. Any help is appreciated.

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Old 02-05-2014, 07:27 PM   #2
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You may or not need it, it depends on if you have vibrations. That said if you can afford it, just of it! You will not need the TC drop so you gain ground clearance, but you will need shims to set your differential angle with the SYE.

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Old 02-05-2014, 08:21 PM   #3
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Quote:
Originally Posted by reno92 View Post
you will need shims to set your differential angle with the SYE.
Good advice^^

The other thing to take into consideration is that the slip yoke could slip off the tail shaft when your suspension is flexing. It could either completely slide and fall off or it's possible that the tail shaft could brake if there's too much stress on it. I watched it happen to a friend of mine, not fun to watch. If you can, add the SYE and a CV drive shaft and definitely take Reno92's advice on the shims.
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Old 02-05-2014, 10:10 PM   #4
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I'll be installing one sooner than later. I just did the 4" RC & I have vibration issues from 35-45 mph even with the TC drop & new U joints.
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Old 02-05-2014, 10:28 PM   #5
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I've got the RC 4" AND 1 1/4" lift boomerang shackles and I'm still on the factory shafts. Mine vibrates pretty bad anywhere over about 35 MPH also. I'll be doing the SYE soon.
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Old 02-05-2014, 11:21 PM   #6
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Here is a little info for those with vibes.

If you retain your original drive shaft you need to check how far out the slip yoke is after the lift. If it is too far out you may lose the shaft on the trail while the suspension flexes or it may go far enough out and then snap.

Solution remeasure the length and have it fixed or lengthened.

For the vibes you can go to Tom Woods home page at Tom Wood's Custom Drive Shafts - Tom Woods Custom Drive Shafts Custom Driveshafts Specialist
and go down the right side to the grey banner under technical information and Sponsorships. Select Technical information and go to the header for Geometry 101.

Without a SYE installed the angles are different and with your current lift from whatever company you need to determine the angles with a magnetic angle finder found in any good hardware store or Harbor Freight. Without the SYE the rear needs to be parallel to the T-Case output.

With the SYE installed you want to be 2-4 degrees lower.

It is illustrated in the article.

When I installed my lift I had the vibes and felt like I ruined my YJ. But I found the supposed to be 6 degree shims were actually almost 9 degrees. I went to 4 wheel parts got some 6 degree shims and I was good to go.

So read the article and understand what happens when you lift, when you install a T-Case drop or a 1" motor mount lift. They all have an effect and there is no magical formulae. You have to do the angle measurements and get the pinion angle correct and the vibes should be gone. At worst they will be so minimal you almost don't notice it.
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Old 02-05-2014, 11:35 PM   #7
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Very good info jokerchief, thanks for posting. My shaft looks identical to the pic on the left (for CV shaft). I guess the shims that came on the RC springs are too much? I believe if I bring the rear down with lower shims I'll need to get a longer shaft. As it sits I have about 3.5" in the tailshaft.
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Old 02-06-2014, 12:12 AM   #8
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Keep in mind that shaft will move as the suspension tucks up and down so you have to have enough movement both ways.

If you are in doubt of the shims after measuring your angles pull the shims out and measure the angle. Then decide how much change you want they come in many different angles check out whats available from the parts sites but get steel not aluminum.
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Old 02-06-2014, 12:23 AM   #9
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Very good. Pretty sure this is where my vibes are coming from. I'm gonna jump on this first thing in the morning once I warm the shop up.

It's 12 degrees outside right now. Poo on that.
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Old 02-07-2014, 07:03 AM   #10
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? regarding shims... Im not really mechanical, where do the shims go?
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Old 02-07-2014, 10:18 AM   #11
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Quote:
Originally Posted by yjjeep89 View Post
? regarding shims... Im not really mechanical, where do the shims go?
They are bolted ontop of the leaf springs by center pins with the thick part facing the front of the jeep

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