Death wobble

[Rollin_Thunder]

I was driving my truck Friday on a highway and it started giving me a death wobble. The front end went all squirly and my sphcinter muscle got a workout. When I pulled over I shook the front end down but couldn't find anything loose. Could it be the wheel bearings?

 

[chengny]

Are the foward drivetrain universal joints tight? Are the both front axles fully disengaged at the wheel hubs?

The front wheel drive train utilizes 4 universal joints. One at the end of each axle (within the framework of the kingpin) and one at each end of the drive shaft.

Note: actually on a 1 ton truck, the rear end of the drive shaft is coupled to the T/C with a CV joint rather than a u-joint.

If the wheel bearings are okay (they would have to be ready to fall apart to cause the vibration you described) and the steering linkage is reasonably tight, the cause is most likely an extremely worn out u-joint.

I'd drop the rear end of the drive shaft first (easy, four bolts to the T/C output flange).
You can't really do a good inspection with it still bolted up, it has to be dropped.


With it released from the drivetrain, twist it, hit the joints with a hammer, stick a screwdriver into the joint and pry up and down....whatever. You should be able to easily determine whether either joint is shot.

The u-joints at the outboard ends of the axles can be checked in place. Insert a bar or big screwdriver through the openings of the kingpin and, while rotating the axle, pry up and down on the joint if one is bad enough to shake the truck you'll know it right away.

Here's the thing though:

For this vibration to have occurred the front drive train must have been rotating.

It could have been being powered from the T/C as is normal when the 4WD is intentionally engaged or it may be that one of your hubs is not releasing at the wheel hub. In that case the drivetrain would have been being powered backwards from the road wheels.

Check the locking hubs for proper function. With the wheel up, and the hubs set to free, rotate the tire while looking through the opening of the kingpin. The u-joint should not turn as the tire is turning. I would lock and unlock each one a few times to make sure that they are releasing every time.

Check that the T/C is not powering the front driveshaft when 4WD is not selected. This is easy too. While you have the D/S out, and the T/C is in the 2WD position, try to rotate the output flange. It should spin freely. Stroke the shifter linkage through all the positions several times.

4L & 4H - the output flange should not turn.
N & 2H - the flange should spin free.

 

[bucket]

The K30? It's usually something like tie rods, worn king pin bushings, or worn leaf spring bushings.

 

[kleedus]

how are your tires are they balanced if so are the weights still there

on my old blazer with 38'' tsl's and a dana 60 i went threw everything. bearings bushings king pin rebuild with washers to tighten the springs rebuilt the whole axle with an arb locker and off road design cross over high steer

i refused to belive my tires were the cause they were in great shape.

but it ended up being the tires and all the local shops did not want to balance the 38'' tsl tires

put on a set of 35'' bfg mt's and it was gone

 

[towjoe]

my old V3500 wrecker is starting to get the death wobble when I slow down and stop. I know front axle joints are in need of replaced soon, could they be problem? I know the lockouts are released tho and everything turns freely. I replaced the steering dampener and it helped for a few weeks and back to it again. I can't bring myself to beleive that with 400k miles the front end could be wore out yet???? I know we jacked it up and everything was tight tho exept axle joints, so this post brings up a good question of what else could be problem

 

[kleedus]

rotate tires and see if it changes

 

[crazy4offroad]

Death wobble on a 1-ton is almost always kingpin bushings/springs, or lower kingpin bearings, or caster angle.

 

[Rollin_Thunder]

Ok cool, thanks for the info guys. I'll look it over and see what I can do to fix it over the Christmas break. Hopefully it stays cheap, because my school budget sucks if things break.

 

[crazy4offroad]

Kingpin bushings/springs kit was really cheap at a local driveline shop, $21 for both sides. You dont need the kingpin itself, it is nearly impossible to change anyway. If your tires are a little bigger than stock you can stack a couple washers (no more than 3/16" worth) on top of the kingpin spring to make them tighter. But usually the old bushing gets egg-shaped inside and needs replaced. Lower kingpin bearings are a little more expensive, I think I gave around $34 per side but it comes like a kit with a 2 piece cone bearing and a grease seal, and cap. Adjusting caster on a kingpin axle truck consists of using degree shims under the leaf springs. I've come to find 4* helps correct camber on a truck like mine with 6" lift springs + Offroad Design Super Shackles front spring shackles. If the bushings, springs and bearings (if needed) doesn't correct the problem post back the specifics of your suspension setup and we can help get it dialed in how much shim you need to correct the camber angle.

 

[Rollin_Thunder]

Ok thanks crazy. It's a stock setup, I haven't had the extra money to lift it. But I'll tear it apart and take a look. I'm just waiting on a paycheck so I can do more than observe. Thanks for the help though.