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redrubiLJ 12-22-2010 02:02 PM

front end vibration (i know, i've searched)
Here's my stats up front. 2006 LJ Rubicon. 4" lift with new Currie LCAs, factory UCAs. 33" MTZs, new shocks, Rock Krawler adj. front trac bar w/drop bracket, drop pitman arm, Rock Krawler discos. Recently aligned and tires balanced, everything torqued to spec.

Here's the problems:

Had a front end vibe, that I assumed was drive shaft, so I pulled it and took it to a reputable shop in the area, and they checked it and the front u-joint near the pinion was bad, so they replaced it. They checked the rest of the drive shaft, cv joint, and checked the balance and said it was all good.

I put the shaft back in, and am still getting a vibe from around 45 mph and up. It's not as bad, but still there. Pinion angle for the front shaft is spot on (directly in line with the driveshaft, checked with angle finder multiple times). Had a t-case drop I took out, put it back in. With the t-case drop in or out, and after checking pinion angles, I still get vibes.

If I pull the driveshaft, I don't notice the vibes anymore. If the shaft is in and I put it in 4wd, the vibration is gone. Back in 2wd, vibe is there. All the U-joints in the front driveshaft are greased, and so is the CV joint.

The initial notice of the vibration lead me to believe that it was the front driveshaft, but after having it checked, I'm not sure of that.

Is there something else in the front end that could be causing this "pulsing" vibration in the front end that is just being transmitted through the driveshaft when it's connected? I'm out of ideas, and the shop is closed for the holidays.

Not being able to figure this thing out makes me want to drive it off a bridge :banghead:

JeepCreeper 12-22-2010 02:17 PM

Are the tires new or newer? I had the same vibrations you describe. Mine was partly due to uneven wear on the tires because of infrequent rotation.

redrubiLJ 12-22-2010 02:21 PM

The fronts are in great shape, the rears are a little more worn. I've tried rotating them, and it doesn't really make a difference. Also, even if it is the tires, wouldn't I notice the vibe even with the front driveshaft out?

redrubiLJ 12-22-2010 05:25 PM

anyone else have ideas?

shrubeck 12-22-2010 06:02 PM

I have EXACTLY the same problem with my TJ, and unfortunately I have no idea what's causing it (I even have a HP d30 in front). The new Tom Woods front shaft made it better, but it's still there. The bushings in my lower front arms are shot, so I can't dial in the pinion angle. When I fix that, I'll try some different pinion angles. It may also be something with the front output bearing of the transfercase or the pinion on the front axle, but neither are noticably loose on my Jeep. There is a pretty extensive thread about it on JF... with no solution. One thought they have is that with low gearing, the front shaft is turning faster than shops will balance it at. But I don't know about that since you don't vibes from the rear on your LJ right? What axle gears do you have? Have you tried having the front pinion high or low a couple degrees?

redrubiLJ 12-22-2010 07:22 PM

I've tried adjusting the pinion angle, with no luck. I have the stock Rubicon gears still in there. Tonight I bought two new U-joints and a centering ball for the CV joint in the driveshaft, so we will see if that helps once I get those installed.

Same with me, no discernible movement in either the t-case output shaft or front pinion. We will see what happens with the new joints installed. I know the reputable shop I took them to said they were ok, but I figure if you're going to do one, might as well do them all. Should have that done in the next couple days. I'll post any updates. This may be the last straw for this rig if I can't get this figured out. There has to be a point where you just quit throwing money at it, and I think I am about there...

Twt_74 12-22-2010 07:35 PM

I have the same problem. I read somewhere an adjustable rear trackbar may help. The stock bar even with a relocation bracket, doesn't allow the proper geometry which causes front end issues. As soon as we get through the hollidays I'm ordering from qtec. A buck thirty I believe.

shrubeck 12-23-2010 01:13 AM

I haven't heard that before, but I'm open to any possible fix. Let us know if it works.

Twt_74 12-23-2010 07:20 AM

Sure will. Happy hollidays yall

Twt_74 01-04-2011 08:49 PM

Replaced the rear track bar yesterday. The shimmy disappeared! I have a very slight vibration at about 50 mph that's gone before I hit 55. I think that's just a tire issue. Hope it helps your problem.

roloplex 01-04-2011 10:51 PM

friend of mine is going thru the same thing. Lot's of people say that " It's a lifted jeep, it will never be perfect". It is driving him crazy. A shop did say that it is his rims. Steel rims that are not perfectly round

Hardcoreheath 01-05-2011 09:00 AM

Is your front end centered? Your side to side angle could be off on your drive shaft, the same way the up and down angle can be.

If it's not centered, adjust your trackbar till it's centered, then (YOU HAVE TO BE ON FLAT GROUND FOR THIS TO WORK SO YOUR DRIVELINE DOESNT BIND UP WHEN YOU GO BACK TO PARK TO TIGHTEN THE BOLTS) slightly loosen all your transfer case skid plate bolts and crank the jeep up, go from park to drive to reverse, a few times then back to park. Kill the engine and retighten the skid bolts. Reset your toe to as close to absolute zero as you can, DIY, it's super simple with a friend and a tape measure.

redrubiLJ 01-05-2011 08:18 PM

Well, got it figured out...

After having the driveshaft inspected by a "reputable" driveshaft shop to initially fix the problem, and their response being that it was just the front u-joint, the problem was still there. I had a pretty good idea after that it was still a driveline vibe, because as previously mentioned, it went away with the driveshaft out.

So I took another look at the driveshaft, pulled it apart to do a full rebuild on it, and the cv centering ball was toast (weird, because the driveshaft guy said it was fine). There were needle bearings that had been ground to sand, and it was dry as a bone (even after he said he greased it for me).

Instead of replacing the cv joint and doing a full rebuild right now, I said screw it, and ordered a brand new Coast Driveline shaft, and everything is smooth as butter. When I finally get around to rebuilding that front shaft, I guess I'll have a spare.

I learned two important things when trying to diagnose this issue, as simple as it was:

1. Always get a second opinion.
2. Find a new driveshaft shop.

Happy Jeepin!

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