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Causes and inspection for 'death wobble'


tcslr
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What kind of car? Kingpins? Leaf spring shims on a beam axle? Tire balance? Worn tie rods? Pitman arm? Steering box? Shocks? Alignment?

 

Some cars may have specific death wobble issues that people may know how to solve. It isn't a catch-all kind of situation where all cars have the same problems. Telling us what kind of car it is can help you get the answer you need.

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Check tire pressures first.

 

From there, go to wear and alignment issues.

 

From there, check whether axle is bent.

 

Wobble seems to only occur on straight axle cars.  If axle is straight, tire pressures are correct, and adjustments correct, then the next possible cause is worn out parts on the front end.

 

I've seen too many cars that were "100% restored", but if you ask the questions find out that nothing was done to restore the front end because "it was good enough".

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Back in the late 80's, had a set of new Lester tire 6/50-19 tires on a customer's car. The positive caster was excessive. While inspecting the jacked up front end I spun the wheels to check for concentricity and wobble.   The right front tire had a 1/2 weave in just a few inches roll of the tread. Hit a slight bump just right and it would set up a front end shimmy that would rip the steering wheel out of my hands.   Only way to stop it was to stand on the brakes.

 

I corrected the caster,  moved that wavy tread tire to the rear axle, and it never happened again.

 

Paul

Edited by PFitz (see edit history)
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Its the 1929 Chrysler.  This only happens very rarely.  When both tires hit a hard raised ridge, it occurs, like a railroad crossing perpendicular.

Tire pressure is right on.  Wheels are balanced.

Tire wear proper - I have not yet checked caster.

Wedges look OK - not cracked. King pin play seems reasonable.

It is a straight axle, with leaf springs.

 

Do most of you do your own caster measurement? I've never done it but it looks not too difficult.

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Toe-in, draglink play, steering box slop, etc, wobble is usually due to some play somewhere that allows a modulated frequency to occur (similar to a wheel out of balance) and requires a slow down to stop it. I've never had to deal with caster on these old cars, but s'pose it could be a factor as well. You said "King pin play seems reasonable"? When front end is jacked off ground and front tire is grabbed at top and bottom and flexed vertically, there should be no discernable play. If noticeable play, you may have the culprit.

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Ten or more years ago I diagnosed a major death wobble on a friend's 1930 Pierce as due to the wrong size "adapter" or "carrier" on the inner front wheel bearing seals.  The correct steel shell wheel bearing seals have been unobtainium for decades.  You've probably seen the semi-pliable red plastic adapters to extend a smaller-diameter seal outward to the wider dimension needed to fit in the hub's recess which receives the lip.  In this case, the "lip" of the red plastic carriers/adapters was deeper than the recess by about 1/4-inch--with the effect that the hub and drum could not be firmly seated against the spindle backing.  That is, the hub and drum would bounce back, even against tightening the spindle nut.

 

Solutions included (1) find a different adapter/carrier with less lip protrusion, (2) laboriously trim the existing adapters to protrude less, and (3) machine a deeper recess in the hub.  Don't know what he did--he sent it back to the dealer for repair.

 

Apologies for the terminology substitutions 🙂

Edited by Grimy
corrected spelling (see edit history)
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On my '32 Chevy I experienced the death wobble twice.

Thankfully I was going only about 25 MPH when it struck but WOW.

I experienced in a few times in the '19 Model T I had too but that';s a different setup entirely.

This Chevy was purported to be a very low miles car which was substantiated by the original owner's family.

At any rate I was driving and the steering column tube came out in my hands......YIKES.

I stopped, pushed it back and drove home slowly where I tightened it<<< that part is relevant to the rest of the story.

There also was too much steering slack which made it uncomfortable to herd down the road.

Long story short is the final cure was taking up end play in the steering box.

Due to the low miles it never dawned on me until recently that the looseness of the steering tube allowed the adjusting nut on the steering box to turn as the tube also squeezes on the adjusting nut to help hold the setting.

 

 

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One of my 1931 DBs had a death wobble. I took it to the local tire place next door. They found two shims between the springs and axle on each side. One shim/wedge on each side was broken. They took the broken shims out of each side and left one in on each side. Never had another problem.

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