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Discussion Starter · #1 ·
i get a pretty bad vibration from about 65+ that gets worse with speed. T5 tranny, 3:73 rear btw. It feels like it is in the driveline, but still does it when in neutral at 65+. i thought it was one of the axels, replaced both and it is still there. from what i can tell the driveshaft is fine...Any suggestions? its driving me crazy.
 

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how are the U-joints? were the gears installed professionally? its very easy to mess up a gear install. other than that, how is your driveline angle? does the crossmember that the trans bolts up to bent or warped in any way? what about tire balance or wheel bearings?

All of these are a good things to check.
 

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Like stated, it could be the DS or ujoints. Know anyone around that you can swap a driveshaft from for a few minutes? It only takes a 12mm 12 point wrench and a few minutes and will save you a lot of time troubleshooting. While yours is out, replace the ujoints anyway. If that is not the problem, move on to the other suggestions.

General note with driveshafts and ujoints. The higher the gears, the worse a bad DS or ujoint will feel. A slightly bad one might not be noticeable with 2.73's at 65 but terrible with 3.73's at 65 mph.
 

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meh
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When I bought my 89 5.0 the drive shaft was dented. It vibrated pretty bad at 65 and got worse as you went faster. It has 2.73 gears. It didn't matter if I had it in gear or not. As long as the car was rolling the driveshaft was turning.

I took the driveshaft out and got it balanced and new u-joints ($45) but it had been like that so long (previous owner) that the transmission yoke was worn down 0.5 mm. I had to replace that as well.

It fixed the problem.

During all that I learned its a good idea to put some (red) loctite on the driveshaft bolts. I tightened the hell out of them but they backed out every time. (strange clicking noise at low speed = loose drive shaft bolts) Red loctite fixed that.
 

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wheel weight came off,or u joints, or your girlfriend left one giant vibrater under your seat..
 

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Discussion Starter · #8 ·
u joints are fine....wheel bearings are new in both sides....the transmission is new also...not sure if it came with a new yolk but i will check...i know one rim is not perfect, but it is able to be balanced so i dont think it would cause the issue. I guess i will check the drive shaft and recheck the tire balance....thanks guys for the input.

btw, when i replaced my axels, i noticed that the 9 or so bolts holding the ring gear on were loose. 3 of them were backed out about 4 threads and coming close to completely f-ing up my rear end. i tightened them all and there was no change to the vibration...so i dont think its the rear end.
 

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I would also suspect u-joints. But I have heard the transmission input shafts can get bent easily and cause this. This would be a last-case scenario.

How did you check the u-joints? Take them off or just wiggle the driveshaft. I couldnt tell by wiggling, but when I took mine off, one of the bearing caps was full of powder.
 

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Discussion Starter · #11 ·
the new tranny came with a new input shaft as well...doubt its that...i have some MM lower control arms to install. i guess i will take a close look at wheel movement, u joints, drive shaft while i have it jacked up.

it weird..at times it sounds and feels like the vibration is coming from the rear somewhere, and other times it sounds and feels like it is right under my feet...
 

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Discussion Starter · #12 ·
i just wiggled them...
 

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Discussion Starter · #13 ·
ok so i jacked the car up and ran it at about 25 and couldnt see any movement or off balance of the wheels. Driveshaft spun nice too.

But, when i jacked the car up and put the ebrake on, i move the driveshaft, and it definately is moveable. Should it move AT ALL, or if so how much?
 

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it might turn slightly like an 8th of an inch or something....you said you had 3.73's just curious what are rpm are you at when its doing the vibrating?? is it around 2500 or more? Reason i ask is this, we figured it out after talking to a mechanic from ford for 30 years that also had a few drag cars, and was telling us that ford only balances their drive shaft to 2500 rpms from the factory, so alot of people that put gears in their cars will notice a vibration at higher speeds due to that.
 

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Hold the part where the DS attaches to the rear, so the slack in the gears is isolated. than wiggle the DS. If it moves, u-joints. Same thing just happened to me except mine was at 80mph.
 

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meh
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it might turn slightly like an 8th of an inch or something....you said you had 3.73's just curious what are rpm are you at when its doing the vibrating?? is it around 2500 or more? Reason i ask is this, we figured it out after talking to a mechanic from ford for 30 years that also had a few drag cars, and was telling us that ford only balances their drive shaft to 2500 rpms from the factory, so alot of people that put gears in their cars will notice a vibration at higher speeds due to that.
Driveshaft speed has absolutely NOTHING to do with engine RPM's. The driveshaft turns the RPM of the rear wheels multiplied by the differential gear ratio. For example, if you have 3.73 gears, that means the driveshaft turns 3.73 rounds for every one round of the rear wheels.

The drive shaft spins if the back wheels are turning. Which means you can take your car to 80mph, put it in neutral and shut the engine off, and the drive shaft will still be spinning.

In a drag car with a significant amount of HP/TQ, you don't want to run a stock driveshaft because they are too weak; not because of balance issues.
 

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and rpms aren't limited to the crank either now are they??
 

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Discussion Starter · #18 ·
to check the u joints, do i try to rotate the DS or move it around?

And i couldnt find any relation to RPM and the vibration...it does it at 65+ in gear and in neutral.

it probably does it at lower speeds to. i probably discount it as engine noise and vibration.
 

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it should wiggle back and forth if its the U joints
 

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everything you have said points to u-joints. If you have never replaced them than just yank em out and do it. Bet it fixes the problem. It won't rotate but it will wiggle back and forth slightly. any movement is bad. you wont believe the difference it will make when you replace them.
 
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