# Bad vibrations



## [email protected] (Nov 24, 2008)

67 GTO vibrates above 55 mph. I have balanced all wheels, replaced u joints, and balanced the driveshaft. Front wheels are not vibrating and steering wheel is quiet. The shakes come up through the seat. Any suggestions. Car is 400 auto with 3:23 posi. Stock car with unknown miles but not a low miles ride. Any suggestions?


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## busaben (Oct 30, 2008)

[email protected] said:


> 67 GTO vibrates above 55 mph. I have balanced all wheels, replaced u joints, and balanced the driveshaft. Front wheels are not vibrating and steering wheel is quiet. The shakes come up through the seat. Any suggestions. Car is 400 auto with 3:23 posi. Stock car with unknown miles but not a low miles ride. Any suggestions?


has it always vibrated, or is it somthing new? looks like you've already checked most of the rotating parts, you might wanna check your axles. if its the same rpms that vibrate, regardless of speed you could check the balancer. im no spert, but it may be worth a look


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## Rukee (Feb 8, 2007)

Put the rear end up on jack-stands and run her up to speed. If it's a bent axle, an out of center wheel, or a broken belt in the tire you should be able to see it when it's spinning.


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## geeteeohguy (Feb 2, 2008)

Isolate the powertrain from the rolling chassis: At 60mph, when it's vibrating, push in the clutch and let it coast at idle. Still vibrate? Then it's axles, hubs, wheels, drums, driveshaft out of phase, or diff. Vibration go away? Then its in the engine/trans. You put in new u joints, etc, but are they phased correctly? Did you check driveshaft run-out? 
Jeff


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## Tri-Power (Jan 10, 2008)

like I said in your other thread:
I bet i know. When I first got done with my frame off I left the rear differential alone. I didn't even check for proper backlash. Anyways, I had an extremely similar vibration. Anything above 60mph was a pretty serious vibration. After driving it a while, I noticed that the vibration was significantly decreased under moderate to heavy acceleration (you should check that). And the vibration was severely amplified when i was "rev-matching" at that speed (in gear, but holding the engine RPM to a coast speed. (neither engine braking or accelerating)). Anyways, it ended up being play (backlash) between the ring gear and carrier. If i had to guess I'd say that is your problem. Properly rebuilding my diff fixed my vibration.


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