[sloth92]

Okay I am going to try this again My wife has a 95 mercury cougar with the 4.6 and at certain times it will vibrate like crazy almost like only the rear end is going over the little yellow dot markers on certain roads and then sometimes it will do it like the roads that have little cutouts on the shoulder to wake you up if you vere off a little bit. Now I have changed rims I have made sure tires are new and balanced and replaced the brakes. I would know for a fact that it was transmission problems if it happened at a certain RPM but it doesnt it very sporadic, My grandpas mechanic was dumbfounded too I was just hoping that some mn12 expert may know some kind of direction to point me in

 

[JustinH]

There is an excellent writeup on this subject, you might want to use the :search: button and look around.

Some oddball things I've seen. Brake rotor runout on my car caused a wicked vibration.

Also loose subframe bolts cause a vibration.

What about the driveshaft?

 

[master486]

I'm betting on trashed motor or trans mounts, specifically the trans mount.

 

[Chris_Murder]

Trans mount, motor mount, low on tranny fluid, broken elements in rear suspension, unbalanced tire, worn swaybar bushings, bad shocks, etc... etc... there are so many things this could be, start with the obvious.... is anything in the suspension loose? how old are your rear rotors? does it do this while braking? does it do this while accelerating? does it do this while shifting? does it do this while coasting? does it do this while revving and coasting? were your tires balanced? were they torqued right? were they tightened properly? answers to these will help slightly

 

[sloth92]

I have done the brakes and rotors and the tires are balanced and I took rims off my t-bird which are fine also and it still did it I can never pin point when it happens it is very sporadic it will do it when driveing and through hard accelerations and normal driving I am stumped .

 

[raven]

Do a search for TC Shudder problem, if it sounds like your rear wheels are running over rumble strips. Most of the time changing the transmission fluid to Mercon V cures it.

 

[IcemanV8]

Definitely sounds like torque converter shudder. I'd say everyone on the board has experienced it, unless their car already had Mercon V put in it. Does it do it worst around 35 - 55mph, just around in there? It's more of where the RPM is at, but those are known speeds that the problem occurs. Mine was diong it bad, and I changed my fluid with some Mercon V, and it hasn't done it ONE time since. Well, after the first 5 minutes of me getting the fluid through the tranny good, it really hasn't done it since then. It will feel like you are running over some bumpy ****. When it first happened to me, I was like "WTF WAS THAT?". All is good now, go with a transmission fluid change before it's too late.