The driveshaft is about the only thing I haven't replaced, so it is still the stock iron one that came with the 84.

I have noticed that when I floor it, I get a vibration which is more noticable at the higher mphs. Is this a sign of an unbalanced driveshaft?

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1984 z28 w/ a 357 cu in. monster engine which is looking like the posterchild for Edelbrock with the exception of the Holley 750vac... all the suspension stuff... 9-bolt posi disk is in...

-=ICON Motorsports=-

don't know if this helps,last month I replaced both u-joints,two weeks later I replaced the transmission mount with a poly one. I noticed a vibration around 2000 rpm and higher. I checked everything, took off the driveshaft to grease the u-joints even more. I noticed just behind the yoke there are two very thin disks, one disk didn't go around all the way, I thaught it might be a small weight , to make things short, I turned the driveshaft where the the weight tabs are the oppisite side, no more vibration

Usually when you have driveshaft imbalance, or tire imbalance, it happens w/ speed, regardless of accel or decel.

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Is the vibration correlated to engine RPM, or to car speed?

If it's engine RPM, look at the flywheel, balancer, accessories on the front of the motor, etc.

If it's car speed (take the car out of gear and coast and it's still there) look at driveline stuff.

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"So many Mustangs, so little time..."
ICON Motorsports

sounds like the vibration i chased in my iroc and could never find or fix. finially got a new set of t/a radials for the back and found 2 quarts of water and mud inside the tire, vibration all gone now.

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ICON Motorsports

1st & 3rd

i had a similar prob mine was a grinding and vibrating noise in all rpms check your torque converter bolts mine were loose causing vibration its a shot