BAlford Posted August 11, 2002 Share Posted August 11, 2002 I have a 1982 280ZX with a 350 eng and turbo 400 trans. I am feeling a slight vibration. I have had the tires balanced. It feels different than a tire shake. Its not in the steering wheel. I suspect it is in the drive train someplace. I just installed another rear end in the car. The vibration was in the car with the old rear end about the same. It is hard to explain, it does it all the time. I start to notice it at about 2500 RPM and higher. It is not constant. It comes on and then goes away with a duration of about 10 seconds. It is very slight, much much less than the vibration when you drive on the asphalt sholder of the road that is designed to alert you that you are going off the road way. I supect that it is the drive shaft or one of the CV axels. Any ideas? Quote Link to comment Share on other sites More sharing options...
BAlford Posted August 11, 2002 Author Share Posted August 11, 2002 Your use of "beating" is a good term, that is about how it is. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted August 12, 2002 Share Posted August 12, 2002 If I read this correctly, you are sensing a "beating" (similar to a twin engined aircraft with the engine rpm slightly different from each other). I can't imagine what would cause this other than one tire being worn more than the other side, making it shorter, thus causing it to spin slightly faster (or front-to-back too if there is a difference in the two sizes and they were just off balance enough to feel). A drive shaft U-joint would not exhibit this "beating" effect because they are both fixed to the same shaft, thus making them a more constant vibration. Quote Link to comment Share on other sites More sharing options...
BAlford Posted August 12, 2002 Author Share Posted August 12, 2002 I made a special effort to time the vibration and it cycles every 3 to 4 seconds. It builds up to a peak and then drops off to nothing. Quote Link to comment Share on other sites More sharing options...
pparaska Posted August 12, 2002 Share Posted August 12, 2002 That definitely sounds like a beating phenomenon. Basically, two things are vibrating at frequencies that are very close to each other. This is one of those things that the OE's deal with and design out of their cars. I'd try to change the stiffness of the mounts for the tranny or the diff to see what happens. Oh, even if the u-joint angles are the same, the driveshaft still speeds up and slows down a bit ast it rotates at a constant input speed. Matching the u-joint angles just lessens the effect. Check out my driveline mods page and the spreadsheet there to study that phenomenon. Quote Link to comment Share on other sites More sharing options...
Guest greimann Posted August 12, 2002 Share Posted August 12, 2002 It could also be a harmonic that is comming from something unrelated to the drivetrain like engine vibration or exhaust system. Like Pete said, auto manufacturers put a lot of effort to into tuning out these types of annoyances and for a garage hobbiest, it is going to be trial and error situation. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted August 12, 2002 Share Posted August 12, 2002 I have an earlier post in this category relating to a new vibration troubleshooting tool - Vetronix MTS 4100 (http://www.vetronix.com) - that is THE way to locate the source of vibration, noise and harshness. Check around the big shops in your area, particularly Ford dealerships. Quote Link to comment Share on other sites More sharing options...
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