Jeep Cherokee Shakes, Wobbles and Vibrations.

Does your Jeep shake quiver, tremble agitate, brandish, bump, chatter, churn, commove, concuss, convulse, discompose, disquiet, disturb, dither, dodder, flap, flicker, flit, flitter, flourish, fluctuate, flutter, jar, jerk, jog, joggle, jolt, jounce, move, oscillate, palpitate, perturb, quail, quake, quaver, rattle, reel, rock, roil, ruffle, set in motion, shimmer, shimmy, shiver, shudder, stagger, stir up, sway, swing, totter, tremor, twitter, upset, vibrate, waggle, water, wave, whip or wobble?

Nothing ruins a great drive in a Jeep faster than the many shakes, wobbles and annoying vibrations that can occur. These problems are made even worse when you start lifting the suspension and adding bigger tires.

The most common cause of shakes and vibrations in a Jeep are the tires. Jeeps use rather large tires often with heavy tread and with stiff sidewalls. All these factors add up to a rough ride if the tires are not well cared for.

Another common source of vibrations are the drive shafts. These rotating shafts have to be perfectly straight, and in proper alignment and balance to run smooth. Often the drive shafts can be misaligned as the Jeep is lifted or if the springs are damaged. They can be easily bent or knocked out of balance through off road use.

The most startling of all Jeep shakes is what we call Death Wobble. Death Wobble is the very scary sensation that occurs when the front wheels start to flutter like bad shopping cart wheel. The only way to deal with it while driving is to slow down until it quits. Right after your life flashes before your eyes.

Lets us look at the tires first. Other than being round and black, truck tires are very different from passenger car tires. Truck tires have much stronger sidewalls and thicker heavier tread. Both of these factors mean they may need much more weight to balance them. Also, as the tread wears the balance may shift.

Also, it is very easy to knock off a wheel weight when driving off road or sometimes move it to another place on the rim. Mud can also build up inside the rim and rocks can lodge in the tread. Any foreign object like this will cause an imbalance.

When you have a speed sensitive vibration, look first to the balance of the tires. It may be necessary to use an internal balancing system to deal with the changes in balance cause by tire wear.

Drive shaft vibrations are sometimes hard to diagnose. When you suspect a drive shaft vibration, start by inspecting the U joints. Make sure all the U joints are properly lubricated and have no slop. Replace them as necessary.

If your Jeep is lifted or has sagging or twisted springs, the drive shaft alignment may be off. Just couple of degrees of pinion misalignment can cause serious problem with the drive shaft. Also note that the alignment used for a double cardion shaft is different from that of a single tube with a single U joint at each end.

To isolate a drive shaft problem, try driving the Jeep with out the front drive shaft. The front drive shaft is easily removed and you can quickly tell if the vibes go away when the shaft is removed. To drive without the rear drive shaft, you will need some way to plug the transfer case if you have not modified it with a slip yoke eliminator. With the rear shaft removed and a suitable transmission plug in place, you can drive your Jeep using front wheel drive by placing the transfer case to the part time 4X4 setting.

Drive shat work can be expensive so it is often cheaper to swap in a used replacement rather than having yours fixed. Look for any warps or dents in the tube and replace the shaft if you find any problems.

Death wobble is normally a combination of factors. While stock Jeeps can have death wobble, it is much more common on lifted Jeeps. Bigger tires and the angle of the control arms exaggerate the already unstable inverted Y steering of the Cherokee.

Do not attempt to mask death wobble with a steering stabilizer. Replacing or adding a steering stabilizer may appear to correct the problem, but it will simply be masked until the source gets worse.

The most common source for death wobble is the track bar. Usually it wears at the frame end. This is a tie rod style joint with limited flexibility. If you have lifted your Jeep, you have already used up much of its range of motion and it will be easily damaged if the axle drops lower.

To test the track bar, place your hand on the axle end joint and have an assistant move the steering wheel back and forth. If you feel any play in the joint at all, the track bar needs to be replaced.

Note that many aftermarket track bars have poor life expectancy. I have found the ones from Crown Automotive to be well made and reasonably priced. Let me know if you need a quote on one.

Another common cause if the track bar is OK is wear in the control arm bushings. The axle end upper joint is sometimes damaged by oil dripping from the air box if blow by is an issue. The bushings are difficult to replace in the control arms them selves and it is sometimes cheaper to buy new control arm than to buy the two bushings.

Other things to check are the bolts that hold the steering box to the frame and slop in the pitman arm. Worn tie rod ends can also contribute to death wobble.

In extreme cases or where you have to drive a Jeep that is subject to death wobble, try altering the steering alignment a bit. Toe out will usually stop death wobble. It will wear the tires, but it will stop the wobble. I also fixed one by removing all the caster shims from the lower control arms.

Follow these guidelines and you will be driving a smooth running vehicle that can take you anywhere. Just realize it will take some attention to details to keep your Jeep running smooth.

Jeep Cherokee Spark Plugs

XJ FAQ

Many people ask about what spark plugs I recommend in the Jeep 4.0 engine. I prefer the Champion RC9YC. Many people cross this to the Autolite 3923 which I have also used successfully. However Lee of Hesco has this recommendation:

The plug for the 4.2L head that works is the RC12YC @ .037 gap, if you get ping try RC9YC @ .045 gap. The 4.0L head likes the RC9YC @ .040 GAP.

In my daily driver I am currently running the Champion RC9YC with a .045 gap.

I have experimented with things like the Bosh platinum and other expensive plugs. However the standard Champion plugs seems to work the best. The Autolites work almost as well and will do when I can’t get the Champions. Lee says that the Autolite is a hotter plug and can cause pinging.

Fed Ex Package tracking

Last week I ordered a Headlight assembly for a friend. She hit a bird on the way home form Florida and busted her headlight on her Jeep Liberty.

According to the Fed Ex tracking it was shipped on the 22nd. According to Fed Ex it is still in transit from Texas 8 days later.

I did hear about a Fed Ex plane crash. Maybe my package was on that plane.

I may be stuck with a headlight Assembly if she decides to get her Jeep fixed somewhere else.

Replacing the Harmonic Balancer on a Jeep Cherokee

To change: Remove the belt. Consider removing the front bumper as you will be working through the access hole behind the front bumper.

Auto Zone has both the removal and installation tools in their loan a tool program. Often they won’t know about the installer tool but they have it if you insist.

Run a screwdriver through one of the slots in the balancer and use that to hold it while removing the bolt.

Attach the puller and use to remove the balancer.

Pay attention to the key in the crank.

Install a new seal while you are here.

If possible, heat the new damper slightly. Don’t use a torch just a hot air gun. carefully align the key with the slot in the pulley and press the damper in place. Make absolutely sure the key is lined up. If not it will be pressed out the back damaging the front cover. Ask me how I know.

Assemble the installation tool and use the 1/2 20 adapter for the crank threads. Do not attempt to use the regular bolt to press the damper on. You will damage the crank snout.

Press the damper in place using the installation tool. remove the toll and replace the bolt. Again us a screwdriver to hold the damper while you torque the bolt to specs.

Jeep Repairs

This weekend I helped Jenny change the transmission mount on her XJ. While we had the cross member out we decided to remove the transfer case lowering blocks. This drop was put in to match the tapered lift blocks that came with her lift kit.

We removed the spacers and replaced the tapered blocks with flat blocks.

A test drive showed that the drive shaft vibes were back. I guess the drop is necessary for the 92. I have the same lift on my 88 with no transfer case drop and no drive line vibes.

We spent Sunday afternoon putting the transfer case spacers back in and replacing the flat blocks with the tapered blocks.

The drive line is now smooth again.