Post by Deleted on Dec 14, 2015 11:17:32 GMT -8
Norm Layton wrote:
"Death wobble" is what we used to call "shimmy." It has to do with any suspension that has a continuous tie rod (which nearly all solid axles have) to connect the front wheels.
Shimmy is normally cause by aftermarket application of larger tires, lifts that change the front axle setting for toe, or caster and camber, or a combination of worn or damaged parts. An out of balance tire, a broken tire cord, a bent wheel, or worn shocks can be the cause.
Worn or damaged tie-rod ends, steering box, steering arm ends or a worn steering stabilizer can also all be causes, as can improper alignment. Most shimmys present themselves at certain speeds and go away at higher or lower speeds, some are severe enough to require coming to a complete stop. They can be scary to the first timer who is not expecting such violent behavior after hitting a pot hole, railroad track or a simply accelerating past the point of the damaged components triggering speed.
Most shimmy is associated with improper toe-in or toe-out, in combination with oversized tires, but any of the conditions listed above can cause it.
It is similar to but not associated with, a vibration at certain speeds caused by a lift that creates a too severe driveline angle and imbalance in the propeller shaft (driveline).
They are easy get in a modified Jeep, harder to find for the inexperienced. They have nothing to do with design, until those design parameters are tampered with, or damaged. It's been around since the 1950s or earlier and is not limited to Jeeps.
"CherokeeVision" added, "Do not mistake an unbalanced tire or bump steer for death wobble. A steering stabilizer may help dampen the effects of an unbalanced tire or bump steer but does nothing to fix those conditions. Death wobble is like the vehicle is hooked up to a paint can shaker. If it ever happens to you, you will know it. ... aftermarket products such as suspension lifts are designed to flex at slow speeds off road. This is not the same as engineering a suspension to function properly on road."
Bob Sheaves wrote,
"Death wobble" first showed up in vehicles in the 1960s with early aftermarket lift kits, primarily on Jeep CJs and Land Rover S1s. The steering linkage was a single rod from the pitman arm down to the tie rod, attached at both ends with a ball joint (tierod end) called the draglink; and a single rod from the left to right knuckle that was the tie rod.
With the 1984 Jeep XJ, a Haltenberger linkage modified this arrangement somewhat. Now, it was a single rod from the pitman arm to the right hand knuckle with tie rod ends at both ends for the draglink; and a single rod from the left hand knuckle to the drag link with ball joints at both ends.
These parts are sized in compression strength and torsional strength for the OEM (original equipment) maximum size tires and no larger. In stock form, flexing out of plane for these pieces is minimized.
Once you change the tire size to a larger overall diameter, you do 21 things....both bad. You increase the rotating mass, increasing the gyroscopic effect of the tire on handling, as you also change the theoretical length of the arm resisting the toe change from ground induced inputs.
This is the cause of the steering induced effects. Other issues arise from the changes in the geometry when a panhard rod is added to the system, which causes an over-constraint of the suspension geometry (which is why the proper name of the Jeep "Quadracoil" suspension is "5 link, over constrained, link-coil" suspension.
In a properly designed XJ suspension, the motion of the draglink (of the Haltenberger type) and the panhard rod is supposed to be a parallelogram...but in stock form, it is not, so raising the vehicle even 1 inch worsens the "fight" between the track bar (common name for the panhard rod) and the draglink, causing the tires to steer the vehicle instead of the driver.
In stock form, these effects are minimized. Lift it and you will have a problem, the only change is when and under what conditions. Idiots that simply bolt on a 4" lift kit without understanding what problems it causes will be selected by Darwin...the only question is when. This is one of the prime reasons I call the aftermarket a seller of trinkets and trash. In general, that ain't a single person designing these lift kits that know what they are doing. There was one exception, but they went out of business from what I heard because their kits, which minimized these problems, were too expensive by the consumer (remember my definition of consumer and customer). This company was Nth Degree.
The Rubicon is at the ragged edge of acceptable street and offroad suspension geometry motion. Given the GD&T variance of the production design, it "could" (I am not saying "will") occur, but it will not be to the amount of a 36" tire equipped vehicle.
Norm added again,
The steering damper is not a "fix," it's a band-aid used to mask issues with either worn components or poor design. Dampers did not start appearing on stock vehicles until the late 70s, mostly associated with the trend to larger (wider thus heavier) tires on older designs. Rather than redesign the entire front-end geometry, AMC found it less expensive to add the damper.
On a properly designed and well maintained system, a damper's purpose is to mitigate the effects of bump steer and the sudden encounter of unexpected objects, such as hitting a rock in a trail at 50 miles per hour.
On an improperly designed and/or poorly maintained system, a damper is used as a crutch to mask issues with suspension and tire errors.
Jeeps and other vehicles experienced shimmy way before the 1960s, and before the advent of lifts and larger tires. Worn components are just as much at fault as jury-rigged suspensions.
Diagnosis:
... Any steering column movement is controlled by the direction of the associated linkage and arms, so side to side, or up and down is directed by that. Is it more prominent at certain speeds?
If you follow the steering column to the linkage you will see that "up and down" is really Push and Pull and indicates that the gear box is experiencing front to back forces. [If you have that movement], you need to investigate that immediately. It could be the steering gear mounting bolts, loose or worn control arm ends or bushings,or any number of associated components.
The best way to find them is to place the entire vehicle on jack stands so that the suspension does not have weight on it. That also makes moving and turning components, including the entire axle assembly, by hand much easier.
ImperialCrown added:
If the steering damper (stabilizer) itself is wet with oil and the oil is not dripping on it from above, the plunger rod seal has failed and the internal damping hydraulic fluid has leaked out or is low. This will cause "death-wobble," and yes, it can take the steering wheel right out of your hands.
It doesn't necessarily take aggressive driving for it to fail. Ford, GM and Dodge trucks do it as well. Rack and pinion steering set-ups seem to do it much less than parellelogram linkage steering configurations.
There is a TSB #19-003-07A that addresses a wrong damper orientation issue in LHD JKs (Wranglers) built before 4/4/07. This "mismounting" made the damper prone to possible damage/leakage.
"Death wobble" is what we used to call "shimmy." It has to do with any suspension that has a continuous tie rod (which nearly all solid axles have) to connect the front wheels.
Shimmy is normally cause by aftermarket application of larger tires, lifts that change the front axle setting for toe, or caster and camber, or a combination of worn or damaged parts. An out of balance tire, a broken tire cord, a bent wheel, or worn shocks can be the cause.
Worn or damaged tie-rod ends, steering box, steering arm ends or a worn steering stabilizer can also all be causes, as can improper alignment. Most shimmys present themselves at certain speeds and go away at higher or lower speeds, some are severe enough to require coming to a complete stop. They can be scary to the first timer who is not expecting such violent behavior after hitting a pot hole, railroad track or a simply accelerating past the point of the damaged components triggering speed.
Most shimmy is associated with improper toe-in or toe-out, in combination with oversized tires, but any of the conditions listed above can cause it.
It is similar to but not associated with, a vibration at certain speeds caused by a lift that creates a too severe driveline angle and imbalance in the propeller shaft (driveline).
They are easy get in a modified Jeep, harder to find for the inexperienced. They have nothing to do with design, until those design parameters are tampered with, or damaged. It's been around since the 1950s or earlier and is not limited to Jeeps.
"CherokeeVision" added, "Do not mistake an unbalanced tire or bump steer for death wobble. A steering stabilizer may help dampen the effects of an unbalanced tire or bump steer but does nothing to fix those conditions. Death wobble is like the vehicle is hooked up to a paint can shaker. If it ever happens to you, you will know it. ... aftermarket products such as suspension lifts are designed to flex at slow speeds off road. This is not the same as engineering a suspension to function properly on road."
Bob Sheaves wrote,
"Death wobble" first showed up in vehicles in the 1960s with early aftermarket lift kits, primarily on Jeep CJs and Land Rover S1s. The steering linkage was a single rod from the pitman arm down to the tie rod, attached at both ends with a ball joint (tierod end) called the draglink; and a single rod from the left to right knuckle that was the tie rod.
With the 1984 Jeep XJ, a Haltenberger linkage modified this arrangement somewhat. Now, it was a single rod from the pitman arm to the right hand knuckle with tie rod ends at both ends for the draglink; and a single rod from the left hand knuckle to the drag link with ball joints at both ends.
These parts are sized in compression strength and torsional strength for the OEM (original equipment) maximum size tires and no larger. In stock form, flexing out of plane for these pieces is minimized.
Once you change the tire size to a larger overall diameter, you do 21 things....both bad. You increase the rotating mass, increasing the gyroscopic effect of the tire on handling, as you also change the theoretical length of the arm resisting the toe change from ground induced inputs.
This is the cause of the steering induced effects. Other issues arise from the changes in the geometry when a panhard rod is added to the system, which causes an over-constraint of the suspension geometry (which is why the proper name of the Jeep "Quadracoil" suspension is "5 link, over constrained, link-coil" suspension.
In a properly designed XJ suspension, the motion of the draglink (of the Haltenberger type) and the panhard rod is supposed to be a parallelogram...but in stock form, it is not, so raising the vehicle even 1 inch worsens the "fight" between the track bar (common name for the panhard rod) and the draglink, causing the tires to steer the vehicle instead of the driver.
In stock form, these effects are minimized. Lift it and you will have a problem, the only change is when and under what conditions. Idiots that simply bolt on a 4" lift kit without understanding what problems it causes will be selected by Darwin...the only question is when. This is one of the prime reasons I call the aftermarket a seller of trinkets and trash. In general, that ain't a single person designing these lift kits that know what they are doing. There was one exception, but they went out of business from what I heard because their kits, which minimized these problems, were too expensive by the consumer (remember my definition of consumer and customer). This company was Nth Degree.
The Rubicon is at the ragged edge of acceptable street and offroad suspension geometry motion. Given the GD&T variance of the production design, it "could" (I am not saying "will") occur, but it will not be to the amount of a 36" tire equipped vehicle.
Norm added again,
The steering damper is not a "fix," it's a band-aid used to mask issues with either worn components or poor design. Dampers did not start appearing on stock vehicles until the late 70s, mostly associated with the trend to larger (wider thus heavier) tires on older designs. Rather than redesign the entire front-end geometry, AMC found it less expensive to add the damper.
On a properly designed and well maintained system, a damper's purpose is to mitigate the effects of bump steer and the sudden encounter of unexpected objects, such as hitting a rock in a trail at 50 miles per hour.
On an improperly designed and/or poorly maintained system, a damper is used as a crutch to mask issues with suspension and tire errors.
Jeeps and other vehicles experienced shimmy way before the 1960s, and before the advent of lifts and larger tires. Worn components are just as much at fault as jury-rigged suspensions.
Diagnosis:
... Any steering column movement is controlled by the direction of the associated linkage and arms, so side to side, or up and down is directed by that. Is it more prominent at certain speeds?
If you follow the steering column to the linkage you will see that "up and down" is really Push and Pull and indicates that the gear box is experiencing front to back forces. [If you have that movement], you need to investigate that immediately. It could be the steering gear mounting bolts, loose or worn control arm ends or bushings,or any number of associated components.
The best way to find them is to place the entire vehicle on jack stands so that the suspension does not have weight on it. That also makes moving and turning components, including the entire axle assembly, by hand much easier.
ImperialCrown added:
If the steering damper (stabilizer) itself is wet with oil and the oil is not dripping on it from above, the plunger rod seal has failed and the internal damping hydraulic fluid has leaked out or is low. This will cause "death-wobble," and yes, it can take the steering wheel right out of your hands.
It doesn't necessarily take aggressive driving for it to fail. Ford, GM and Dodge trucks do it as well. Rack and pinion steering set-ups seem to do it much less than parellelogram linkage steering configurations.
There is a TSB #19-003-07A that addresses a wrong damper orientation issue in LHD JKs (Wranglers) built before 4/4/07. This "mismounting" made the damper prone to possible damage/leakage.
