Shaky Silverado - Help!

chevrolet
silverado1500

#1

I have a '99 Silverado 1500 with a 4.3L V-6 amd 188,000. It picked up a problem recently that’s been stumping me. Occassionally, and for no reason I can sort out, it starts to shimmy badly. This behavior has come about at several speeds. Sometimes just cruising down the road at 35-45 it starts to shimmy and wobble and the steering wheel shakes as if a wheel is horribly out of balance. Other times this occurs at highway speeds - it’s noticeable and alarming. The problem can last a long while; othertimes the symptoms disappear in a few seconds. The first time it happened I thought I had a flat or was about to lose a wheel - this is not a subtle problem.

I’ve checked several things and came up empty. No delamination in the tires and nothing out of round, but just to be sure I had the wheels balanced and rotated - the balance was spot on when checked. Alignment is good. Did those things, but the symptoms continued. The vehicle is high mileage so I put in on the lift and checked the front-end. The steering rack has a very slight amount of play and the hub bearings have a very small amount of play too - I’ll get after those, but they’re not causing this intermittent problem. Everything else is tight. Shocks are fine, brakes are fine, I checked the rear-end as well - everything is straight and true. Air pressure is set correctly. I checked the driveshaft for runout and play - that’s not the problem. The truck has never been in an accident and nothing seems misaligned.

The truck drives like a new truck most of the time, then suddenly, on a smooth road, it starts wobbling around. I’m starting to believe the problem might lie under the hood. I had a problem some time back with misfiring and the truck bucking - this turned out to be a worn distributor. A new distributor, rotor and wiring solved that problem. But these symptoms are not similar - this is not a bucking problem; the entire vehicle starts to shimmy and wobble with the steering wheel vibrating back and forth. It’s hard to tell, but I cannot detect any misfiring or rough running in the engine when these symptoms appear and I have no ‘check engine’ warnings.

Are there any engine/transmission/drivetrain related issues that could cause intermittent symptoms that feel like an out of balance condition?

A few other facts:

  • I have noticed the truck is a little down on power lately
  • The fuel economy has dropped off - I used to do around 20, now I’m down to 16mph highway
  • (Very) slightly rough idle

Thanks for any advice you can give!!!


#2

You shouldnt feel any feedback through the steering wheel if it were an engine problem. I would check the a arm bushings and ball joints. You could have a caster problem that wouldnt necessarily cause the truck to pull.


#3

Did you check the ball joints properly? On these trucks (2WD and 4WD), the suspension has to be loaded for any looseness in the ball joints to be detected. In other words, raising it up on a lift and shaking it down won’t show bad ball joints. I normally jack it up by the lower control arm to get the tire an inch off the ground and stick a long pry bar underneath the tire, lift up on it and watch for play in the lower. The upper is checked by grabbing the tire at 12 and 6 o’clock and shaking it while watching the upper ball joint for play.


#4

Jgarewal and mark9207-

Thanks for the feedback - heading out to inspect it again. And you’re right - I screwed up and jacked the entire car up forgetting that doing so loaded the joints hiding any play I might see. Let me do this the right way and report back. At nearly 200K miles I suspect I will no find either a bad ball joint or tie-rod, or both.


#5

mark9207

You were right on! I went back and took another look… the way you suggested and found a bad passenger side lower ball joint. I should know better than this, but was moving too fast and not thinking. Thanks again for taking time to lend a hand!


#6

Hopefully that solves your problem. For the record, if memory serves me correctly, your lower ball joints are held into a stamped steel control arm by three or four rather large rivets. Removing them without damaging the control arm can be a real pain, so unless you have an oxyacetylene torch, grinder, air hammer and bits, and a great deal of skill using them, you may want to consider farming this one out. Having both done at the same time may also be prudent. The new ones will be held in with nuts and bolts.


#7

Had the same exact problem with my silverado. Jacked it up by the control arm and found a lot of play. Wheel hub assembly is cheap and easy to put on. Runs great now.