I had a thought while driving the Roadmaster yesterday. It's got a vibration that I'm not sure where it's coming from.
My question is, if you wanted to trace a vibration could you use the frequency of the vibration to find out what shaft is vibrating? At a given speed just about every shaft in a car is turning at different speeds. It stands to reason that if you knew the vibration frequency and the shaft speeds, two of them should match up.
I'm fairly certain the Roadmaster vibration is in the driveshaft, but it would be neat to have a tool and a database so you could just take a drive and have an answer. Sometimes the butt meter isn't too precise.
Betcha the vibration is coming from the very rear, that was a common complaint on those cars when I worked for the Buick place. The rear frame 'horns' on the wagons are so long they can vibrate via harmonics like a tuning fork. (It's actually the R&P that causes it, BTW so swapping/balancing driveshafts won't help. But binding U joints can contribute to the shake.) Make sure the trailer hitch is bolted solidly to the frame and that the rear body mount rubber is not squashed.
As far as a database, well you got me there.
You could use an accelerometer to find the frequency of the vibration. Sometimes (many times, if its the engine) this will be a second or third order vibration, so if the frequency doesn't match up, divide by two or three and try again.
We're using systems like that on aircraft. Permantly mounted accelerometers throughout the aircraft wired to a computer box with memory storage that you can download and see history and trends. Started years ago with temporary mounted on components for inspection intervals. Side benefit on aircraft is it is extending time change intervals on components. Often removing the time change requirement and changing it to condition change, when it hits a certain vibration level it gets changed. We call it condition based maintenance. But you have to know the frequency of the vibration to know where it is coming from. Every moving part has a resonance/vibration freq range and knowing that will determine where the vibration is. Not knowing will just confirm that you have a vibration at a certain frequency. No help without a baseline.
I have a spreadsheet here. You plug in known values (final dive, transmission and so on) and use a sirometer to figure it out. Basically, the sirometer gives you the requency of the vibration, the spread sheet points you to the source.
If you need it, shoot me a PM.
DrBoost wrote:
I have a spreadsheet here. You plug in known values (final dive, transmission and so on) and use a sirometer to figure it out. Basically, the sirometer gives you the requency of the vibration, the spread sheet points you to the source.
If you need it, shoot me a PM.
What he said. I got mine free from a NVH class.
