PLEASE ADVISE vibration in 5th gear

[BNAZ]

I've begun to get a humming vibration that almost feels and sounds like a bad u-joint. Sometimes its louder with stronger vibration, Kinda like a rolling vibration. Last night I noticed that it goes away if I drop down to 4th gear.
I'm now at 3100 rpm ( 75mph - 3:55 gears 6 wks old ) but it runs smooth again.
When I shift back into 5th (2400 rpm) the brrrrr-brrrrr-brrrr begins again.
It doesnt feel like it coming from back but more like tranny. Does anyone know what it could be and advise me. Thanks

 

[bronco4x4]

It could be the u-joint or the driveshaft is out of alignment. Has it always done this and if not has the driveshaft been removed at some point?

 

[Sicarius428]

Typically people switch to an aluminum driveshaft when they get gears done. 3.55 isnt all that radical but it can make the difference. Your U-joints can be going out too. Get under the car and give the drive shaft a good tug in different directions.. not enough to drop the car on you. Just a thought.
Kevin

 

[bronco4x4]

Usually theres a yellow mark somewhere on the flange that goes into the back of the rear end and on the driveshaft. This is the position where its balanced. But if its not there anymore, your gonna have to try all 4 positions.

Aluminum driveshafts aren't only for vehicles with 3.73 gears and 4.10s. ALOT of cars and trucks and vans made these days have them from the factory. The point is that aluminum absorbes the vibrations much better than steel.

If you had a aluminum driveshaft, you could take it off and put it back on in any position, and never get any vibrations at any speeds.

Usually on mustangs, an out of balance driveshaft causes vibration on the highway around 75-80mph.

 

[BNAZ]

Why do I only feel it in 5th gear. If it was the the d/s or u-joints wouldn't it continue vibrating when put into 4th gear. It completely stops. This sort of lead me to think it probably wasn't the d/s or joints, even though there would be an improvement with the FRPP aluminum d/s.

 

[BNAZ]

I will check the u-joints for play tonight. Does anyone think its the transmission.

 

[Darkwriter77]

I'm getting the same thing at about 50mph after installing my clutch the other day. Bolts are all nice n' tight with threadlocker on there, and I marked the driveshaft's position before removing/re-installing, but perhaps the simple act of removing it somehow angered the Steel Driveshaft Gods. I will attempt to appease them by clocking the driveshaft (removing, rotating 180*, re-installing). If all else fails ... well, I was wanting a new aluminum unit, anyway...