94 K2500 Suburban shakes

[swedishbricks]

Hi folks,

As the subject states, my '94 suburban *occasionally* shakes at hiway speed (50-60). It is beginning to happen more often now.

The symptoms seem to me to be nothing like a tire balance issue...certainly not like balance problems I have had in the past. What it is doing these days shows no issues until running at hiway speeds for a few minutes. I then begin to feel a slight vibration...I can even hear a rumble before I begin to feel it. The vibration and noise grows steadily worse with maintained speed. If I allow the truck to coast to a stop, the vibration subsides as the speed decreases; however, if I brake to a stop, the vibration continues and is even made worse by a vigorous shaking right down to a complete stop as if a rotor were seriously warped. If I then get the truck up to 40mph or so and brake to a stop, no shaking at all but a nice smooth stop. If I get it back up to hiway speeds, same thing all over again. It seems as if sometimes turning a corner may have some relation to whether or not it does this on the next stretch of hiway.

Could this be bearings? Ball joints? What else might produce this kind of behavior?

Thanks for any insights!

-- Matt Brown

[Ralph Curry]

It doesn't sound like anything I've experienced before, but is a little like a bad U-joint.

I'd check that all the lugnuts are tight. Then have the U-joints checked out (or do it yourself). Lastly, if you got the lifetime wheel balance when you bought your las set of tires, then exercise it.

After than, I can't think of any other simple herminic (im)balance issue, but next I'd dig into the front suspension.

[twaddle]

Hi there,
Put the parking brake on and the transmission into nuetral.
Check the rear prop shaft and universal joints for wear.

Is the whole vehicle vibrating or is it just through the steering or brake pedals?

If the prop shaft checks out ok jack up each wheel one at a time and check for movement in the bearing and spin them to listen for bearing rumble.

Good luck

Jim Twaddle
Biggar, Scotland

[rjschoolcraft]

This sounds very much like out-of-round brake drums (or out-of-flat brake rotors). As you run at highway speed, the "high" spots will rub on the shoes (or pads) causing heat generation. This causes an uneven temperature distribution which makes the "high" spots swell and become "higher" making them drag worse and so on. This can actually cause a dynamic imbalance that shakes the vehicle badly.

Once everything cools down, the shake will go away...for a while. I just recently replaced both rear brake drums for this type of symptom. I got rid of most of it, but think rotors are next.