Bad gears=vibration
 

Well guys i did notice my tranny mount is broken but not that bad. Lately the car at anything over 80 vibrates but then when i let off the gas it gets worse. Do you think it is the drive shaft fliped? Or do you think once i replace the tranny mount the vibration will go away. Can a ring a pinion make this vibration? That is what i am scared of but i am almost positive it isnt that because it wasnt doing that before. But who knows can that make that much of a vibration

later

My bad and it is not the wheels.... they are balanced

later

drtbiker,
I went through the same thing with my car (89 LX).

I installed 3:55 gears and out of the blue, I got a weird vibration but only at certain speeds (mostly above 50-mph) and like yours, when I let up on the gas, it got worse.

I was convinced it couldn't be the new gear set so I embarked on a month long mission to find the source of vibration. I went as far as balancing the drive shaft, Flange and Yoke and even installed new U-joints. I became obsessive; I (balance) weighed the bolts that hold the drive shaft to the Flange and even marked my wheels and lug nuts to maintain a baseline! I also used a dial indicator to find the run-out/high-spots on the drive shaft, Flange and Yoke. When I re-installed everything, I countered the high spots by rotating the pieces so the high spots were opposite each other. (I learned this from an NVH guy who works at Fords Research and Development Site)
I'm pretty lucky as my brother works at Fords Research and Development site (in Dearborn, Michigan) so whenever I need a tip, it's no further than a phone call away!

Needless to say, the vibration was not eliminated! It was better but not by much. Now, at this point I suspected the new gear set!
So I installed a new 3:73 gear and the car ran smooth as silk.

It just so happens (Again, Lucky Me) one of my friends brother-in-law works at the Ford Axle plant in Sterling Heights, Michigan. His job is to randomly test gears as they come off the production process. He tested my new (Motorsport) 3:55 gear set and indeed it was bad!

Maybe yours is too.... It happens! Like I said, they randomly test them and if/when one comes up bad, they go back and remove so many that were made before the bad one was found. But some still get past the testing process; it's not perfect. I can attest to that!
Phil

I also had a bad vibration after a gear change and was only at certain rpm's (my speedo doesnt work so i go by rpm) and let off the gas and it got really bad. I balanced tires and rotated the d/s with no luck. I got a new fms aluminum d/s and everything went away.

well i guess i am leaning towards.,... the gears this is going to be a fun one. I just wish i had more time to work on my car. I may have to take it to a shop.

thanks for the
replys

In case i missed it, i would use the kiss principal. Keep It Simple Stupid. Did you check your u-joints?

Well, I've got the same vibration. Anything above 80-85 mph and it starts to shake. When I let off, it's worse until I slow down below the above speed.

I've got several suspects. It is definately not rpm related, just speed related, and it seems to have begun soon after I had the tranny rebuilt. I'm guessing possibly an internal balancing problem. It's not the converter, and it happens in 3rd and 4th gear. I also suspect maybe the old drive shaft I've got. I read somewhere that the hollow shaft is lined with rubber to absorb vibration. As this gets old and dries out, it is possible for chunks to break off and unbalance the shaft. I've replaced U-joints and it didn't help. Also, I just replaced my old drag radials and had all the tires balanced, and it didn't help.

I haven't really suspected the gears because I've had them for over three years and this problem only began about one year ago. Also, the noise from them hasn't changed significantly.

The tranny is under a three year warranty, so I'll probably take it back and have them go through it. Maybe they can check the balance of the drive shaft as well.

--nathan

I think it may be the drive shaft i just havent had the time to get around to work on the car. I am one of those people when i want to work on the car it goes from a 15min job to a 5hr project. I like to look everything over once i get under the car and make sure nothing else is falling apart. Hopefully ill get this mess straightend out

later

I'd bet my bottom dollar It's not the gears. I, like many of you had the same problem at 80 mph. Get the aluminum FMS driveshaft. It's 150 bucks and 2 hours in the drivewayto change, rather than 600 for new gears and install. You won't be sorry. ;)

that is what i am thinking...as soon as i get some time i am going to flip the driveshaft. 180 degrees and see if that makes a differance if not...looks like i am going to start ordering

later

It won't help. You will only move the unbalance to the other side. You will change nothing.

check your bellhousing bolts.

i never thought of that maybe it is...... but i doubt it

later