Hum/vibration/harmonic/whatever

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  #1  
Old 05-01-10, 03:13 PM
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Hum/vibration/harmonic/whatever

Just started troubleshooting this, so I thought I would see if anyone had any thoughts beyond what I already have on my list.

Recently bought a '95 Toyota Corolla 1.6L w/AT. It's replacing college daughter's current car - '96 Escort LE. Normally I would have looked for something newer, but one of the small car lots I deal with came into this and I snatched it up at a very good price; only has 43,000 miles on it (vs 140,000 on the Escort) and it was obviously garage-kept by a senior citizen. It is CLEAN.

Anyway, aside from finding a broken vacuum fitting that I fixed, everything works like new, BUT the car has a noticeable low-pitch hum/vibration both at idle and while driving. On first look I thought I had something loose; among other things there was a loose screw where the bumper cover curves around the right front and attaches to the fender. That corner of the bumper cover had quite the hum/vibrate/rattle going. After tightening that I still have the hum/vibration, so the loose bumper was just a symptom rather than cause.

It is most noticable at/near the right front fender and at its worst it makes the hood prop-rod vibrate back and forth like the low-note string on a cello. It's audible inside,no doubt the sound traveling through the frame/body. I've already eliminated engine-driven accessories as the cause by removing the belts, no change. I've visually inspected the motor mounts and watched the motor while shifting drive to reverse and back. Visually, nothing, but there is a bit of movement when shifting. When I blip the throttle in neutral the sound goes away momentarily and then resumes as the engine settles back into idle speed. My inclination is that this is a motor mount issue, supported by the same opinion by a couple of my favorite mechanics. My inclination is to start removing motor mounts one at a time for a better inspection; actually it probably make more sense to put new ones back on considering the age. One thought I had was to run my floor jack underneath and give the engine a slight lift (different load on the mounts) to see if I can get it to change.

Anyone with ideas I may have overlooked or experienced similar situation? The good news is she's home for the summer so I have plenty of time to tinker with it; mostly it's just a little annoying knowing the car's just not quite right.
 
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Old 05-01-10, 07:45 PM
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vibration

Not familiar with this unit,does it by chance have the "dog bone" stabilizer to keep the motor from tilting during acc.? They can cause this kind of problem.
 
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Old 05-02-10, 05:42 AM
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Will have to look again, but I don't think so, just 4 regular mounts. Logic would seem to point to the mount at the passenger side, but it seems to be solid. One of my client garages mentioned timing belt or tensioner as also capable of producing it [@ 43k miles could be original unless previous owner had it changed already based on age]. Hadn't heard that one before but he's forgotten more about cars than I'll ever know. I'll have to pop off the top section of cover to see if I can get a clue on the age of the belt.

While in motion you almost get an exhaust-like sense to the noise, but when I was under it last week I found nothing loose or rattling in the system and no exhasut leakage noise from any connections.
 
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Old 05-02-10, 08:30 AM
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noise

I have had exhaust systems set up harmonic sounds and be tight (the one im thinking of was on a new truuck) but usually this is at higher speeds. At least you dont have to take it out on the road to hear/feel it. By the way I am just now getting thawed out from my time in Fla. this winter. Who do I complain to?
 
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Old 05-02-10, 10:03 AM
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C'mon back for a repeat visit; temp made 90 yesterday and humidity is up.

I haven't completely discounted exhaust, but the system is stainless so I'm guessing I don't have rusted out baffles or something causing a change in the harmonics.
 
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Old 05-02-10, 12:48 PM
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Any chance of a partially clogged cat? If a chunk is moving around it might make that sound,, not sure though.
 
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Old 05-02-10, 07:48 PM
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noise

They dont have to have anything broken or rusted as I stated the one I was talking about was brand new. But it just did it at like 45 MPH. Had to move it around to eliminate strain. Good hunting.
 
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Old 05-03-10, 05:48 AM
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Well, I tried the slight lift with the floor jack yesterday and that didn't change the sound at all. Not a definitive check for a bad mount, but was hoping maybe it would tell me something. This is one I may just drop off at one of the garages one morning and say, here, fix it.
 
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Old 05-03-10, 12:37 PM
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Going to work out a trade of tows for the labor? Good luck if you are.
 
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Old 05-04-10, 10:51 PM
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Have you ever heard of crank cancer? This is a condtion that occurs when the harmonic balancer bolt has come loose and and wears away at the crankshaft as the harmonic balancer wobbles. it can continue for a long time and needs to be constantly re-tightend. I'v seen key ways totally warn away from both crank & balancer. Ihis always ends badly and the crank & balancer need to be replaced.
 
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Old 05-05-10, 05:58 AM
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Yeah, I thought about balancer, but looks like it was a mount problem. Gambled yesterday on the passenger side motor mount and sitting at idle the hum/vibration is noticeably less. Didn't get a chance to road test it. Will probably also replace at least the forward side mount since it's very accessible; not sure if i'm going to tackle the rear side, it looks like a real dog for working room.
 
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Old 05-05-10, 08:01 PM
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Good luck with it. Hope you have relatively small hands for easier access.
 
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Old 05-06-10, 04:55 AM
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Well, the front side looks like no problem; maybe have to unbolt the cooling fan for a little clearance, otherwise it's a clear shot. The REAR one on the other hand looks as though I would need my daughter's size hands PLUS moving stuff out of the way.
 
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Old 05-06-10, 12:15 PM
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Any chance of her helping you after taking stuff out of the way? When I was growing up, I occaisionally helped my dad with car work. Honestly as a laborer and someone who couldn't sell ice cream to a sumo wrestler, I highly doubt that I am a spammer.
 
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Old 05-08-10, 05:18 AM
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I would say motor mount/mounts. On the left side you can often get a variation of the noise by simply lifting up on the engine by hand.

Those can affect the CV joints too by throwing the alignment of the drive train off.
 
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