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Discussion Starter #1
I know not to many people have six cylinders on here, but I doubt that will make much of a difference as to what is causing this problem.

Car is a 200 ci 6 cylinder Mustang with a C4. Split headers, weber carb, electronic igntion, soon to swap the head with a late model 250 with modified intake.

Ever since I've had the car, I've had a problem with a rhythmic vibration coming from underneath the car - somewhat on the passenger side. The vibration is much more noticeable when the car is cold, and is present only at low rpms when the car is moving. If I'm accelerating from a stop, the pull through first gear and second gear is strong and smooth, but when I'm at the point that I stop accelerate and just maintain speed (between 1500 and 2500 rpms, which equates to about 30-45 mph) the vibration starts and doesn't stop unless I speed up to about 50 mph. Above 50 mph and below 30 it's fine, but between there the vibration gets annoying. It's not gotten worse since I've had the car.

I've replaced the driveshaft and universal joints, and had 2 different rear ends. No difference, but when I switched to the 3.20 rear end from the 2.83 the vibration sped up in rhythm (probably to do with the faster ratio).

Any ideas?
 

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worn tailshaft bushing...maybe...
 

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Discussion Starter #4
Well, I don't think it's a misfire because it's done it with 3 sets of wires.

I'll check into the tailshaft bushing though, thanks guys.
 

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You didn't say anything about the tires or if you have checked for a bent wheel.
 

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I would do a few test's ... locate the rpm the vibs are at, does it repete when parked at that rpm ? get the car to vib speed and toss it out of gear does it stop right away ? touch the brakes when it vibes, Ive seen bad calipers that makes the brake bad's vibrate. were are the vib's felt at? steering wheel,brake pedal,floor,ass,rearward....

open hood and toss it in gear and hold brake. throttle up some and see if motor lifts alittle or alot... maybe a broken mount.

check trans mount.

look for exsaust flanges hitting the frame ect ....

vibrations are a pain in the arse ..
 

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He Said ......

I've replaced the driveshaft and universal joints, and had 2 different rear ends. No difference, but when I switched to the 3.20 rear end from the 2.83 the vibration sped up in rhythm (probably to do with the faster ratio).
 

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Converter out of balance, bad harmonic balancer. But i would do as bartlettracing suggest and try and narrow it down that way.
 
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