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Dash Shakes While Driving

Hoping you guys can help a gal. 1995 Mercury Sable. Car dashboard vibrates intermittently. Two different mechanics cannot find the problem. The car does not do it when it is cold…only when it is warm. I can feel the dashboard vibrating as I am driving. But for some reason, when the mechanics try to recreate the problem, they can’t. It also happens sometimes when I step on the brake. Brakes have been checked, tires have been aligned, rotated and balanced. Town Fair has checked the tires and they are fine. No smells, no noise.

Are you sure it is not the A/C Heater blower causing the vibration?

Will try that out tomorrow. Did not notice if it is on or off when it happens. Will post back. Thanks.

on that note, have you recently (in the past couple of years) had any work done under the dash? like the ac condenser? ac/heater fan? or duct work?

i just thought maybe (just maybe) the dash was nt put back securely??!!

I will have to think back to remember what was done. But will check that out too! Thanks for the suggestions. Will post back.

No work done under dash for the last couple of years. Dash still shakes regardless of whether A/C on or off. Was able to get a repair shop for tires to duplicate the problem. However they could not solve it. Only found a nail in the tire - removed it and patched tire. Now car still shakes but not as much as before. Having another mechanic take a look.

I drive a 95 Sable as well, and my dash vibrates. I have never had any work done to my AC/heater/anything else under the dash. I have noticed it does this at high speeds. I am very good about having my tires rotated/aligned/balanced on a regular basis so it is probably not the tires. I have never had mine looked at for this problem, but I hope in some way my information may help fix this problem.

My 98 Mustang did this. The dealership kept the car many days and returned it saying it was fixed. No charge since it was under warranty. I drove 1/4 mile and returned to the dealer. Nothing was fixed, and I had the same problem. I brought it back. (They were paying for the rental car too.) After several days they called me in. They thought the problem was coins vibrating under my cupholder. I said no, the noise and vibration were in or behind the dash. I drove a quarter mile. U turn. I had the same problem. The service manager said “You can recreate the problem?” I said yes. I had told them originally it happened when I put on the brake in 3rd gear. He said “Can I ride with you when you do it?” I said sure and put on the brake in 3rd gear. A fairly loud vibration and noise started. He said Wow!, because he was expecting something very minor. They improved the problem a lot but didn’t completely fix it. They said the problem was something to do with the transmission and flywheel. Later, when I was shopping for a newer Mustang, they said the factory had solved that problem. I bought another new Mustang from them, and never had that problem again. I don’t know if there is any connection between a Sable transmission and a Mustang transmission. Is there?

I started to leave this thread, thinking I knew nothing of value. As I clicked, I remembered six months in defense contractor vibration testing. When our brilliant engineers (they were brilliant, this is not sarcasm) designed a new box for military use, they had to hook up accelerometers all through the box, then put it on a powerful vibration table, and see if anything was ‘resonant’.

Resonant means something which has a shape and/or dimension which means it tends to vibrate at a certain frequency if it is exposed to random vibrations, or vibrations of a multiple (or sub-multiple, I forget, that was 26 years ago) of its resonant frequency.

Sometimes a box would be solid in general, but on a module inside it, resonance would snap parts right off the board, even though they were glued on with military grade heavy epoxy, and the module would need to be redesigned by the M.E.,s to eliminate that resonance.

Our vibration tables were 400,000 volt-amps, think watts but the difference is the power factor. Once, during a space shuttle launch, they hooked a radio to the drivers so a lot of people could hear the launch via the vibe tables. The vibe tables were essentially loud speakers, for all practical purposes.

The signal used for vibe testing was pseudorandom between 20 HZ and 2000 HZ. It was generated by a computer program, with accelerometer feedback, adjusted at very low level, and when it looked good, the tables would go to full power.

I had been in small earthquakes, but my first full-fledged one was here in the state of Puebla, 1999. I didn’t think I knew much about earthquakes, until I heard that sucker. It by sound was clearly random vibration between 20 HZ and 2000 HZ.

I also understood that the stone walls or house walls which went down were normally perpendicular to the sound waves in the earth from the earthquake. There was no damage parallel to the ground waves, so one could actually tell which way the earth shook.

Earthquakes, except the real high Richter numbers, normally do damage by resonance of the buildings; bridges; etc. All new buildings have heavy concrete columns built around heavy duty re-bar frames, every 10 or 12 feet to avoid resonance. Relevant is the distance a sound wave travels in one cycle in relationship to the distance between columns, not a simple concept to explain. I mean those columns, called castillos (castles) are built right into the wall, not just roof supports.

And, on top of those columns are horizontal beams, connecting the columns, built the same way. All to put resonance outside the normal earthquake spectrum.

Mexico City is so dangerous because it is build over spongy subsoil. An earthquake 50 miles away sets up resonance in the ground itself, and bad things happen downtown.

All this anti-insomnia chatter is to make it clear I think those dashes are resonant at a frequency which actually appears somewhere in that car. Just as Mexico City falls apart with an earthquake far away because of resonance, that dash is waiting and ready for a vibration which is mathematically related to its resonance frequency. A little vibration anywhere in that car can make a very loud resonant sound in that dash.

This is sort of like humming near a guitar, and you can feel the hum in the guitar sound board, except the guitar is usually not resonant, only sympathetic.

Motor; radio; transmission; drive train; tires; mother-in-law’s nagging voice (this one is for Tom and Ray. heh, heh.)

In my opinion, the problem is poor dash design, creating resonance within the normal frequencies experienced in a car.

But, that doesn’t help you. So, assuming your car has not always done this, you need to look for something somewhere in that car that is vibrating. Other examples have shown it can be different things in different cars. And, it may not be that obvious, since resonance has a multiplier effect.

I mean the part which is vibrating may not be that noisy, as long as the vibrations have a mathematical relationship to the resonant frequency of the dash board.

I know of no way to change the resonant frequency of the dash, but that will also eliminate the problem, just like the column and beam structure of my house tends to eliminate wall collapse resulting from resonance. Still, in all examples here, something was wrong in the car.

As a tech finding squeaks and rattles was the most miserable, poor paying time consuming part of the job. would rather stay home. And doing it on flat-rate for the dealer miserable. Its amazing how many people just live with the odd noise when it came to paying serious money to find. If it was a car you just worked on and could possibly be related to your work. You had to find it getting paid or not just hope for a better day tomorrow.