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Discussion Starter #1
got a vibration around 80mph ,parts that have been replaced
driveshaft -1 piece aluminum
rotors -drilled and slotted
wheels-dont mnake a difference-slicks or street tires
new rear with 4.10 gears
it kinda feels like a tire is out of balance in the rear butt the tires are good on balance
any ideas?
mike
 

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Baby Huey
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It probably has been but, is your 1 piece drive shaft balanced?

Mine did that too awhile back but it was the tires, they were egg shaped.

Good Luck :)
 

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When did the vibration start? Was it after the new gears were put in? Wheel bearings good and tight?

Jay
 

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Discussion Starter #4
It Was There When I First Bought The Car.
When Everything Was Still Stock,i Thought The Snow Tires On Back Were The Problem Butt No ,bearings Are Good And Tight
 

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Long shot, but is the transmission secure to the cross member (transmission mount not broken/cracked)? Is the extension housing on the transmission loose?

Also, I am assuming that the U-Joints are fairly new?
 

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Not sure if the 4.6 has this issue, but I know the 5.0 had issues with the harmonic balancer coming apart and causing a vibration.

Jay
 

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Discussion Starter #8
Ujoints Are Good,trans Mount Is Good And Stiff
Once I Get It Up To Speed And The Vibration Starts I Put It In Nutral And Still Have The Vibration,besides That I Have The Bhj Balancer On It
TRIED MOVING THE DRIVESHAFT TO A DIFF BOLT HOLES AND STILL NO JOY
 

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Id drop it in neutral when it’s a little above vibrating speed and let it coast down. If it still vibrates, then you know it isn’t the engine and prob not tranny.

Are your rim’s valve stem lined up with the hub's stud that has a paint mark on it? The stud with the paint mark is the lighter side of the hub.

Edit: I'm retarted, didnt read the above post about the neutral test thing. Dee de dee lol.
 

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O, mybee check for play on the half shafts.
 

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do you have one lug nut biger then the other four if so put it in the hole closest to you air stem. if you don't have one lug on each tire thicker "heavier" then that can cause this problem
 

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Discussion Starter #13
well i have some super coupe rims on the car now ,mo matter what rim tire combo i put on i still have the problem,
was not aware of having to line up the valve stem with the colored lug stug,never ran into the problem on my other mn12 cars,same with the lugnut being bigger never knew
 

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i've heard it a few times and when i bought my car i had vibration issues and tried that and it worked
 

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frankjc said:
Mine vibrates around 100 mph. No idea why.
Judging by where it says you are in your profile. . . .I would probably say it is the lack of a nice smooth road for these kinds of speeds. :) But seriously, do you drive these speeds often or were you just joking around?
 

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I had a harsh vibe that would come up at 80+, a huge difference from 79mph to 80mph. And, it would get far worse as I neared 100+. turned out that it wasnt my crappy tires like i thought.

I can almost guarantee you it is a rubber mount. Be it the driver side motor mount, the trans mount, or the trans crossmember, it could be all 3, could be one also. My trans crossmember was SO TORN that when I removed the trans, I discovered that the horrible vibes were coming from the drivetrain being so out of balance/excess play, that my trans was hitting the underside of the car. There was a nickel sized scuff mark on the top of the trans and the underside of the body. Very small, hardly noticeable, but I can almost guarantee that was the problem. Got it back together, now the only high speed vibes I get are because of crappy roads and it is far better than having the car feeling like it was shaking itself apart.
 

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I had this exact problem...

I replaced the driveshaft and rear end, and it was gone.

I bought the driveshaft thru one of the group purchases, and the rear end from the boneyard.

The rear end had too much travel when I rotated it...play in the gears, or something. My other Cougar was totally different, and that car is fine, so I changed the rear end as well as the driveshaft.

One of the ujoint bearings ws toast, on one side. I didnt take the other rear apart, but it felt totally different than the new one when I spun it by hand.

Good luck; It's always the last thing you swap in these cases, unfortunately.
 

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wether said:
Judging by where it says you are in your profile. . . .I would probably say it is the lack of a nice smooth road for these kinds of speeds. :) But seriously, do you drive these speeds often or were you just joking around?
Dead serious. I don't do it that often though.
And yes, the roads are terrible here.
 
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