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1991 Mustang GT vibration @ highspeed

1757 Views 12 Replies 7 Participants Last post by  discord
I have an evil vibration coming from under the car in 4th and 5th gear at 60mph +. The faster I go the louder it is. It doesn't occur while accelerating but becomes apparant when decellerating. Once I'm on the clutch going this fast, wow, hard vibration, shakes the whole car, but stops after slowing below 60 or so. I've only noticed it in 4th and 5th. Its a 1991 with 3.73 gears. Only has 100,000 miles on it with only bolt on upgrades like headers, pulleys, intake, and rearend. I've checked everything I know. Anybody had this problem? or has any Idea how to fix? Some say drive line, someones else said throw-out bearing, but I dont think its tranny involved. Please help, Thanks
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You can try unbolting the driveshaft and turning it a quarter turn and then rebolting it in its new position. You can do this three more times before it's back in its original position. If it's been out, it may have been reinstalled in a different position. If this cures it, you still might want to look in to new U-joints.
Thanks, I will try it on Saturday and post a follow-up:)
Check your trans tailshaft bushing.If you have alot of slop up in down while pushing on the front of the driveshaft then that will cause the vibration you have described.
If you can point me to that bushing, I will check it, Thanks
discord said:
If you can point me to that bushing, I will check it, Thanks
It's inside the tailshaft housing of the transmission. I have the same problem with my T5 at the moment.

A sure sign of a worn bushing is trans fluid running down the driveshaft. For me, after I've been on it hard and come to a stop, I get a cloud of smoke from under the car where the fluid got thrown onto the exhaust and burned off.

It's a PITA to replace. You will need to remove the tailshaft housing from the trans (some say you can do it with the trans in the car, other say you'll need to pull it), get the old bushing out of the housing somehow (dremel and chisel maybe) while being careful not to damage the bore, and install a new one with a press or a bushing driver of the correct diameter.

D&D will sell you a replacement bushing for about $10.

Don't do what I did with my last T5 and run out of fluid and melt it down. It wasn't pretty. If it's been smoking and stops one day, worry.
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You will need a special tool to remove it and install it.You can do it while in the car.It's not a job for the inexperienced.You can screw it up.
also check your pinion angle exspecialy if it has aftermarket control arms on it make sure its in line.also if you have solid mount control arms that can cause you to fell that vibration.check those very easy to check .also check u joints you:laughlitt could have one even setting up on you very common in n.y just remove it and see if there is any hard spots when you twist it if so replace it .could be lots of things just some to try
Thanks for all the replys I will try the U-joints first and see what happens:)
Driveshaft could be out of balance too. That was the problem with mine. It was vibrating real bad above 50 mph. I put a different driveshaft in it and the problem went away. It has been fine since.
possible tire seperation??:wavey
tire seperation? Lost me there
Well, new U-Joints and still vibrating :( The neighborhood reputable shop named the throw out bearings as the culprit. Very spendy. They also found one tire worn irregularly, meaning out of alignment, so I'll fix that first and see if the shop was right. Tailshaft bushing checked out fine. Thanks for all your help AFM
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