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help with vibration/shuddering diagnosis?

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i posted this over at PPBB as well...

i was driving home tonight and all of a sudden, i got this stuttering vibration like i was driving over rough pavement. i instantly thought that i had a flat tire, and let the wheel loose in my hand to see if the car would pull hard to the left or right, but it didn't. tires are fine.

i was able to make it home ok, but was very nervous. i just hit 100K miles a little while ago, so engine failure has been a concern at this point.

the car is a 97, manual, 103,400 miles. has been driving fine, no problems at all lately. the vibration just started out of nowhere as i was on the highway in 5th gear doing about 65-70mph. when i pressed the accelerator pedal, i got a lugging kind of sound/feeling/vibration that comes from the rear of the car. the vibration/shuddering can not be felt through the steering wheel. i still had power to accelerate, and the vibration didn't seem to increase with rpms. the vibration was not an 'in the washer machine on the spin cycle'-type, violent vibration - it was kind of 'soft' like lugging (hard lugging, though), and very noticeable.

i noticed that when i took the car out of gear (i.e. pressed the clutch pedal) the vibration stopped. when rev matching to the next lowest gear there was no vibration. if i then coasted in that lower gear, no vibration. but when i stepped on the gas in any gear, i get the vibration.

the clutch seemed normal as it always does. no change from the usual. no clunking when changing gears, shifts smoothly, pedal travel/feel normal, etc.

i also did not get a CEL, which i was entirely expecting. at least a CEL would give me a clue! ;)

the wheels do need to be re-balanced, but they are not that far off.

i got the vibration/shuddering at any speed, any gear, any RPM, ONLY when stepping on the gas pedal while in gear. no vibration otherwise (coasting, downshifting and coasting, revving while not in gear, etc.)

i am thinking it could be all kinds of things. any expert advice, or has anyone had a similar experience?


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Sounds like your rubber engine mounts have shot. This causes extreme vibration as you say and a possible 'clunk' when you corner hard.

after reading the symptoms of motor mount failure and CV joint failure, i think it's more likely the CV joint. i'll check the boots to see what they look like.

the vibration is the same whether i am cornering or not (but again, only when accelerating.)

any other help, tips appreciated.

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