traderyoda

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!!!

Allan In NE

Stop driving this truck!

If it is shaking the steering wheel, it's chasis/steering/wheel-tire related. Find a good garage and have it fixed. You don't wanna be in the thing if a tie-rod, idler arm, or ball joint decides to turn loose.

Allan

traderyoda

I certainly agree with that... not looking for a bad day. But I've had the truck up on a rack twice. Couldn't find anything wheel/tire related. Everything in the truck's front-end is original. But there's no play in any of the joints that we've been able to find, and that includes the ball joints.

Could you have a chassis/steering/wheel-tire problem that's intermittent like this?

cleveland63b

cant say ive heard of anything like this being intermittent...is there any change in the steering effort when it occurs?

Johnf1059

Does the truck have a steering stabilizer shock? They can act up intermittently.

traderyoda

I finally solved the problem... here what I did.

First, the steering box and tie-rods were fine, so was the idler arm. This is a 2WD truck so there's no steering damper. I found a worn lower ball joint - since the truck has lots of miles I replaced all four. This didn't solve the intermittent vibration. In fact it happened again, but this time it was so violent it blew out the driver's side shock. They needed to be replaced anyway... so 4 new shocks. Same vibration. The wheels were balanced and rotated - I didn't suspect any problems since the problem was intermittent, and it turns out there weren't any problems and everything was right on. Intermittent vibrations continued... I noticed that if I pulled off the road and waited a few minutes the truck would drive fine again. So I began to get suspicious of the brakes. I brought along a infrared thermometer and the next time it happened I shot temps on the two front rotors. Sure enough the driver's side was running a lot hotter than the passenger side. It turns out that one of the two pistons was intermittently hanging up and failing to retract. It didn't drag enough to cause the wheel to pull. No rotor is perfect and it would pulse the rotor at the high spot as the wheel rotated. The rotor would get hot and expand which increased the magnitude of the periodic impulse going into the wheel. Depending on the speed this would cause tremendous wheel vibration. I pulled the caliber, thoroughly bled the brakes, replaced the rotor and checked runout, and installed a new caliper. I did both sides to keep everything even. Problem solved - haven't felt any vibration since and it rides like a new truck.

I was a little dubious that a caliper could cause this kind of vibration, but when I became suspicious and checked the forums I found a bunch of other folks who've had the same problem. So add "dragging caliper" to the list of things that can cause a violent and intermittent vibration in your sterring linkage!

Thanks to all of you for taking the time to help - very much appreciate it!!!