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WHOA!!!, what was that??? Sudden violent shake on freeway


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OK, did my truck just become possesed, or is there something I am not seeing. This truck is by far the smoothest, quietest Jeep I have ever owned; It'll do 90+ down the freeway and it feels like your driving a Cadi. Today though, I was driving it, a 100% stock '88 MJ 4.0, 4x4 5-spd longbed cruise set going 75mph on the freeway when I came on a change of concrete at which point there was a minor bump between the two sections. As soon as I drove over it my manche began to shake so violently intense, it was like I was driving over offset railroad ties, so bad it felt like the truck was going to tear in half and I was going to loose complete control of it. I managed to get off on the shoulder, but the slower it went, the more violent it was, and the brakes seemed worthless as the pedal was shaking too...I had all my weight on the brake pedal and I could hear the tires screeching with the shake. I got out of the truck expecting a wheel to be half hanging off, or a blown tire or something, but everything was normal. All wheels were tight, nothing was caught in the rims or drivetrain, nothing was hanging off or had fallen off the truck, suspension felt tight...I got back in the truck and drove it, once again got it back up to 75mph, floating smooth as can be down the freeway.

It then happened a second time a little ways down the road as I was taking an offramp, once again right as it hit a bump in the pavement, this time I was doing about 50mph...also this time I was on the brakes when it started, but the last time I wasn't as it was on cruise control. Not as caught offguard the second time, I let off the brakes for a moment to see if that made a difference, and it didn't. I got to the bottom of the offramp, this time equally as voilent as the last, came to a stop, and the truck made it the rest of the way home 25+ miles no problem. When I got home, I jacked the front end off the ground, wheel bearings felt fine, all suspension is tight, wheels are straight, tires are perfect, u-joints are fine...WTF IS GOING ON!?! It is obviously hitting a bump at high speed that triggers it. It has never done this before today; and I am not exaturating (spellcheck) when I say it is a VIOLENTLY INTENSE shake. Any ideas would be much appreciated as I am totally stumped. :hmm:

 

James

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High speed DW is usually caused by a tire balance problem. Lower speed DW can be tons of things. I would have the front tires checked for balance and run out FIRST. If the tires are not causing it start checking everything connected to the front axle to include,

 

ball joints, track bar, unit-bearings, TREs, and all the arm bushings for wear and looseness.

 

Good Luck, DW can be a bear to fix.

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You definitely experienced the dreaded death wobble!

If you own a Jeep long enough, your sure to experience it at least once.

If it's not a constant wobble, I'd rule out tire balance as the main cause, but it can help trigger the wobbles.

What is happening is when you hit the bump, it throws the front end into oscillation, side to side. This doesn't stop until you slow down enough for things to balance back out. It will then be fine until you hit another bump throwing it back into oscillation.

This can be caused by a number of things including the unit bearings, ball joints, worn bushings and steering components.

The most common cause for this problem is in the trackbar. However usually there is more than one thing causing it, and it's often accompanied by worn control arm bushings (even if just a trackbar fix seems to fix it).

Also check the frame side mount, and make sure the axle side mount didn't get wollowed out. While your at it, make sure your steering box bolts are tight too.

Have a helper turn the wheels back and fourth while you inspect the steering components and TB for ANY play. Things may "feel" tight, but there's a lot of force being applied up there!

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Had bad DW on a prior XJ and it turned out to be two different things. Trackbar was worn and the upper control arm busshings were slightly worn . Replaced them all uppers and lowers and then bought a new ZJ trackbar and DW disappeared never to return. Put another 100,000 on that Jeep before giving it to my daughter who is still driving it.

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Yep, now you know what the term "Death Wobble" means. If it is set off by a bump, I would rule out tire balance. My guesses are track bar (frame end), ball; joint(s) or lower control arms (or mounts) in that order.

 

To check the track bar, put the front wheels between concrete blocks and slowly move the steering wheel left and right. If the truck slides left and right over the axle, do it again with someone under the truck looking at the track bar frame mount and see if it moves. It is quite common for the hold in the frame mount to become elongated. A lot of slop creates loose steering. But just a tiny little bit is usually enough to set off an oscillation -> DW.

 

Lower control arms I know of no way to check other than taking them off and inspecting them. Rubber bushings could have deteriorated, control arm could have worn out not holding the bushing in tight, mount bolt holes could have elongated etc. Frame end mount holes are supposed to be elongated, but the little bracket inside (with alignment spacers behind it) should have perfectly round holes snug around the bolt.

 

Ball joints can be tricky. I could not find any play in my passenger side wheel, even with a crow bar. But when I took it apart anyway, the lower ball joint was about to fall apart. Replaced and wobble fixed.

 

Good luck!

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