Vibration, growling at narrow speed range

Cattler · Cattler's Garage

Guys,

I've done a few things to try to correct this problem, but haven't made any headway. Its getting a bit louder, but I haven't noticed any change in handling / performance. Here's what I have:

- Starts at 3,200 RPM / ~70mph; speed dependent (only in 5th gear)
- Growling noise, sounds like its coming from the front end, but I'm not sure
- No loss of power, no hesitation. Can accelerate through normally and it does seem to even out. If I let my foot off the gas, it'll come back when within ~200-400 RPM of 3,200. Goes away below 3,000.
- Never makes the noise at all if I'm driving local roads and don't go above ~3,000 RPM in 5th.
- Sometimes it'll go away after hitting a bump on the highway.

I've had the front bearings replaced and all four wheels rebalanced. The balance was off on all four. No abnormal wear on the tires--have about 10,000 miles on them. Mechanic says suspension looks normal; nothing's hung up or rubbing.

What should I be looking for? I'm likely to bring it to my local mechanic, but I don't want to fund a fishing expedition. Last time I took it in (August) with this problem, he couldn't duplicate the complaint--I get it every time I drive.

Thanks,
David

prschmn · 12-12-2010, 05:03 AM

Judging from your description it's a trans/shifter/enigine deal and not front end. Important to realize that RPM range has a natural harmonic. First I'd open the cover over the shift rod and make sure that's not the culprit-there was a service thing about that ages ago. If not there then I'd suggest looking at engine/trans mounts to see if there any possibility of something making contact when the drivetrain wiggles around. I'm afraid if i didnt find anything there I'd probably be draining/checking gear oil.

Oh Haha · 12-12-2010, 06:25 AM

Do you feel anything in the steering wheel when it occurs? If not, then I would suspect POSSIBLY it's a rear wheel bearing issue.

Do you feel it through the shifter? If so, then look at the bushings and coupler and maybe even fine tune the adjustment so that the shifter it positively in 5th gear and against the tang on the top of the shifter housing.

Pure speculation on both of the ideas, of course.

Cattler · Cattler's Garage

I DO feel it in the steering wheel and not in the shifter (I've tried a light touch on both to check for vibration). How can I check the rear wheel bearings as a limited ability home mechanic?

Thanks,
David

Oh Haha · 12-12-2010, 06:48 AM

Forget the rear wheel bearings for now. The steering wheel is a direct link to the front suspension. Focus on that end of the car.

How long ago were the bearings replaced?

I suggest lifting the front and doing the "tire rock" test to see how tight they are.

Lift the front SAFELY and support on jack stands. Just enough to get the tires off the ground is fine.

Now grab the tire at 9 and 3 and rock it back and forth. Do the same technique but with hands and 6 and 12. You should have no play either way.
Please do this and then post your findings.

I need to get out and start shoveling but others will chime in.

Cattler · Cattler's Garage

Thanks--stay warm. It'll be a couple of days, but I'll try it and post.

Flieger · Flieger's Garage

It could be that the retaining nuts for the bearings have a been set a little too tight or loose, meaning the bearing has just enough play or pressure to cause a noise in those circumstances of rpm.

Oh Haha · 12-12-2010, 11:59 AM

Whilst shoveling I thought of another possibility. The brake calipers may be sticking, not allowing the pad to fully retract. Most times, this is felt at very low speeds but you never know.

Let's check the bearings first and go from there.

Cattler · Cattler's Garage

Well--this one was more complicated. The noise has been gone for a while, so I'm pretty sure the last repair took care of it. When I brought it in for my last oil change, we noticed it was sagging in the left rear--not bottomed out, but trending in that direction.

The spring plate bushings were completely shot and the left spring plate cover was a rusty mess. Replaced the bushings, spring plate covers, re-indexed the rear torsion bars, lowered the front, re-indexed the front torsion bars, and finally a four wheel alignment. I've had the car for a little over four years and its never handled this well! I should have done this a long time ago... Anyway, it must have been binding or dragging on the left rear quarter sometimes under load or cornering.

Here's a recent shot showing the corrected ride height and rake.

Best,
David