Serious Humming Vibration Sound on Acceleration

[Tom Johnson]

I have a 1989 Corvette. When I accelorate from 20mph to 65mph on an onramp to a freeway, I get this deep humming/vibration sound coming from the passenger side front-end. This is very inconsistent as well. To try to issolate the source, I'll put it in nuetral and the deep bothering humming/vibration does not stop. I'll will punch it up to 80mph, then down to 25mph, and there is no change. It will then go away after 10 minutes on the freeway. This is very inconsistent. I have changed the plug wires, distributor, rotar, plugs, etc., but no resolve.

I would take it into the shop, but they would not experience the problem on a test drive, because it is not a frequent enough.

Any one experienced this before?

[Tracy C.]

Re: Serious Humming Vibration Sound on Acceleratio

Tom,

I once had this sound/vibration on a 72 Cutlass. It was the inside inner front wheel bearing race turning on the front spindle. Not sure how your front spindle/bearing set up is on your 89 Vette, but it might be a place to start looking.

tc

[Wayne W.]

Re: Serious Humming Vibration Sound on Acceleratio

Strange, but there are a couple of things that come to mind. I have seen wheel bearings that were subject to impact, side load, make a humming noise on the C4s. Brakes that were not surfaced well will vibrate, but this is usually on braking. The transmission joke on these cars is a source of frequent problem vibration.

[Ralph Harlan]

Re: Serious Humming Vibration Sound on Acceleratio

I can think of several things that can/will cause the humming/vibration you describe. As both Tracy and Wayne mentioned, it could be wheel bearings. Usually you can check this by jacking up the front (or back) of the car and trying to wobble the tire/wheel assy while it is still on the car. I usually will push and pull at either the top or the bottom of the tire to see if the wheel will wobble. I have found over the years that many times it is hard to be sure whether the sound originates at the front or the rear when wheel bearings start to go bad. As it progresses, it will have more of a throb like a freight train. I had bearings go out on my '64 years ago that sounded like the front, but as it got worse it became more obvious that the drivers side rear was out.

Wheel balance can also be perceived as a "vibration" and won't show wear patterns for awhile unless it is really bad. Weights can be lost or shifted while driving causing such a problem. Out of round wheels/tires can also be perceived as a vibration. Usually if it is a front tire/rim it will also be felt in the steering wheel, but if it is a rear, well --. Shifted belts in the tires can feel the way you describe - it only takes one, and it may not be visible until you get the tire off to look closely. Sometimes you can feel a shifted belt by running the palm of your hand around the tire - careful of stones, though.

Universal joints (both driveshaft and axle shafts) can cause a vibration like you have. Several checks for these include sliding under the car and grabbing the shaft next to the joint and pushing/pulling to see if there is any play. Frequently as the joints wear more you will start to hear a "ring" as you shift into and out of gear (auto trans). My mid '70s 4wd suburban had an out-of-balance driveshaft that created a throbbing vibration that was maddening at 45 - 80 mph and it was hard to tell wether it came from the front or rear. When I drove the car it sounded like the noise originated on the passenger side, but when I had someone else drive it and rode in the passenger seat it sounded like the source was on the driver's side. And it got worse when I finally had the driveshaft rebuilt. Turns out the rebuilder rotated the ends of the driveshaft 10 degrees the wrong direction when they put it all back together, so I had to pull it back out and have it redone (after several agonizing months of further trying to determine the problem.)

The same '64 I spoke of earlier had an alignment problem that caused a humming noise, but that was accompanied by a terrific pull to the right in the steering. Tires wore quickly, also. Had an old (dare I say it) Ford that the motor mounts and transmission mounts were so deteriorated they caused the humming/vibration in the speed ranges you described - but I caught on to that when the (manual) transmission started eating teeth on the gears. Had a pilot bushing on my '64 cause a vibration above 20 mph, but it was worse on heavy acceleration. Input/output bearings on the transmission can cause vibrations in that speed range, but (again) it usually gets a bit worse under heavy acceleration.

Never had it happen, but I understand that the harmonic balancer at the front of your crankshaft can age/deteriorate allowing the balance wheel to rotate slightly on the hub causing a vibration (usually at mid and high rpm ranges of the engine). Throw it in neutral or push in the clutch at highway speed so the rpm drops to idle - does the vibration disappear?

As Wayne wrote, brakes can cause vibration, but usually on use of the brakes only - unless you have a caliper not fully releasing or an ABS problem

Good luck tracking it, keep us posted on the findings.

Ralph

[Tom Johnson]

Re: Serious Humming Vibration Sound on Acceleratio

Ralph and Gang,

Thank you very much for your detailed response. The key issue here is that it is not consistent. I would say that this experience has happened three times over a two month period. Strange enough, it was when I drove on a curved on-ramp and when I reached about 60mph, the deep throaty humming/vibration started. I shifted into nuetral (automatic) and drop the RPMs down to 6, and nothing changed. I slowed the car down twice over a two mile period, and then it stopped. The tires a good, and I have replaced the brakes and rotars, front upper and lower ball joints, and rear wheel bearings.

Again, my concern is that if I take it into a shop, they won't experience this, because it is so infrequent.

Any other thoughts would be helpful, and I will post the final results.

Thanks.