ok the car is vibrating at 50mph and up. I checked the tranny mount and its fine. It has new u joints. I tried searching but it gave me an error. this problem is getting to me. any help would be really appreciated.
Thanks

 

around 50 it vibrates when off the gas, but with on it doesnt.

 

Hey there, I have had the exact same problem in my car since I have owned it. I am yet to solve it and have ran out of ideas

 

i had my tires balanced and it seemed to go away a bit. but i think its the pinion in my diff. I guess those gears r not set up right or something is going on in there.

 

I would say if it is changing severity when you change from accelaration-to de-acceleration, it is not a tire balance issue. You may be correct about it being a rear-end issue. Does you pinion seal show signs of fluid leakage?
A bad pinion bearing can cause a vibration as you described and will wear the seal before very long, therefore a leaking seal would be a sign that this is the case. Damage to the gears may have already occured although replacing the pinion bearings and carrier bearings solved the problem on my last 'F' body which lasted until the girl I sold it to flipped / totalled it several thousand miles later.
or
You said " I guess those gears r not set up right or something is going on in there.". Does that mean you have had new gears installed? I am not familiar with any of your past post.

 

Never mind. I searched your username and found this thread .
Did you set the pinion depth correctly when you installed the gears?
That thread is in-conclusive.
My Strange 3.73's took very-different-than-stock width shims to get the pinion depth correct {seems like, from memory, I installed .015 more on the backside and .015 less on the front, for a shallower depth setting to equal the Strange specs.{engraved on the gear}}. The pinion depth guage is expensive, but without it, the gears will not last, unless you are much luckier than I am.
If I had run my gears .015 out-of-spec, as the stock gears were shimmed, my set-up likely would have not have lasted long. But they have ~30k miles and have always been quiet.

 

yea its leaking from the diff. i need to take it to a shop to get the gears readjusted or something. i actually thought id blown my 10 bolt . But I guess I didnt. this happ right after i used drag radials. weird

 

DR's place a good bit of stress on the gears, espesially on a 10 bolt. Did you replace the pinion spacer with a solid one? Hooking DR's tend to put enough stress on the pinion gear to actually compress the spacer more than was initially set up for proper bearing clearance, therefore letting the pinion gear run at a tolerance that will cause pinion-to-ring gear bind, and cause gear failure as well as a vibration as you stated you have.
And to answer my question about the pinion depth setting as I inquired above? What proceedure did you use?
I would say, seeing as how you have a front pinion seal leaking, you probably have a pinion bearing pre-load issue at the least. You may be able to repair the trouble with new bearings and a seal, although if the initial was not set-up for proper 'pinion depth' tolerances, permanent gear damage may be a fact.