Deadweight70

Alright...I have a 1990 5 spd 5.0 mustang thats fairly stock.

My transmission shifter has always vibrated at higher speeds but lately when I'm in 5th gear its starting to get unbearable. I've noticed when I'm in 5th and only in 5th I get a very bad shudder that hits at 55 mph. It almost feels like I'm tapping the brakes while simultaneously giving the car gas. To better describe it.....it feels like something is binding up for a few seconds. Then I accelerate out of it. There is still a vibration there just not as pronounced. The vibration almost disappears by the time I hit 70. If I drop the vehicle into neutral the vibration goes away. If I take the vehicle over 55 in 4th or 3rd I still get a bit of vibration but not the strange dragging feeling that occurs for a few seconds right at 55mph. If I put the vehicle into 5th at a speed over 55 mph the binding feeling never occurs. The vibration is mainly felt in the center to the rear of the vehicle. It is especially strong in the shifter handle.

The clutch feels great. My tires aren't the best. Wheels are not bent. I checked the U-joints last around 15,000 miles ago and they were fine. I have a very very tiny trans leak, a little spotting if I let the car sit for a few days. I used to drive the car daily, 80 miles a day. Now the car sits for most of the week. I have noticed it more since the car has not be driven as frequently. I've had the car since 112,000 miles. It has a 141,000 on it now. I noticed today when I looked under the vehicle that my h-pipe is coming apart at the center of the H. I noticed my car was getting noiser before the vibration problem developed however.

any ideas will help...I'm thinking about changing the u-joints just because they're probably due. I didn't see any problems with the harmonic balancer. If I rev the car at a stand still I get no vibration. Thanks.

westcoast25

I had the exact same problem on one of my other Mustangs. I tried everything and then I swapped out the driveshaft for the Ford Motorsport one. Problem, solved, and it felt like it made it faster!

westcoast25

http://www.summitracing.com/parts/FMS-M-4602-G/

Here is a link for it at summit, it's like $250, but well worth it!

Deadweight70

Thanks for the advice.... I'm gonna put it up on a lift tomorrow and see if I can duplicate the binding feeling while its up in the air.

Deadweight70

well.... checked the u joints and they were good. Transmission fluid was the right color and smelled fine. I welded the exhaust back together. Checked the rear end fluid which was a little low and reeked. Took off the cover. Gears looked fine. No metal shavings or such. Replaced the fluid. I didn't see any weights on my driveshaft. I don't know much about driveshafts to be honest with you and I don't know if it has to have them. The feeling definately got better. The shake in the shifter has diminished but I still get a very strange vibration throughout the car in 5th only around 55 mph.
Geesh and the hole in the exhaust. I forgot how quiet my car really was. The car drives much smoother with a noticable increase in power.

I guess replacing the driveshaft might be the next step

93 LX FiveO

there should be weights on the shaft if its stock

mattparty

i had the same vibration problem with my 91 and this might sound stupid but make sure your bolts on the drive shaft foing into the yolk arnt loose mine came loose and i had the same vibration problem

Deadweight70

It seems like every driveshaft and drive axle place has gone under in my town.....

Am I better off just replacing the drive shaft or should I just get it balanced.There definately weren't any weights on the shaft. How much does balancing a driveshaft normally cost? Any ideas?

I did check the torque on all of the bolts in the vicinity. Thanks for the suggestion.