I replaced all tires, the rear shocks, all brake pads and all calipers, and had my rotors turned. I've also had the tires balanced and aligned. My '99 automatic Mustang starts vibrating when I accelerate from 55mph+ If I let off the accelerator the vibration stops. I just replaced both U-joints today and it decreased the vibration greatly, but it still does it a little bit at 55+mph when I accelerate.

I think it might need another front end alignment or the drive shaft is bent. I don't wanna take my Mustang on the highway until I can get this vibration fixed because it'll get annoying real fast. Can anyone help me out on what might be the problem?

I also noticed that if I accelerate quickly to 3000 rpm it briefly makes a sound as if pebbles are being thrown into a fan or a popcorn bag is at the end of it's popping in a microwave. I'm not too worried about this problem because I rarely hit 3000 rpm but if anyone knows about this also that'd be great!

 

Motor mounts, is the first thing that comes to mind.
Maybe wheel bearings?
Unbalanced driveshaft could definitely be the culprit aswell.....

 

auto or stick? have you had the car since it was new? How many miles are on it? Who balanced the tires and did you rotate them after they were balanced?

 

oh yea welcome to TMS hope you stick around after you get your problem fixed?

 

It's an automatic, it was given to me in February 2010 and was a prior salvage title. It sat for a year in a garage before I got it. It ran fine, just cosmetic work needed to be done. I had it repainted and body work done to it. The odometer read 171,xxx miles on it when I received it, but I can't see how that could be correct. A lot of the parts on it were stock, but some also junkyard parts (transmission). It was owned by a young kid. I put a definite 31,000 miles on it since I got it and most are highway miles.

I had it tuned up when the odometer read 199,200 miles. That's when I found out about the majority of the parts being stock and the transmission not being the original. They were amazed at how well the car was still running given the mechanical shape it was in.

These are the exact things I've had done to it mechanically since I got it.

Replaced:
Front & Rear Universal Joints
Spark Plugs
Air Filter
Fluids
Oil Change
Brake Pads
Calipers
Rotors
Tires
Rear Shocks
Front Sway Bar
Transmission Pan
Transmission Filler Tube
Transmission Gasket

The place that put on my tires said they balanced and aligned my tires also, but I'm pretty sure they didn't do it because they tried scamming me out of $500 for a brake job. In the next check or two I'm going to replace the front and rear wheel bearings, have it balanced and aligned again(I have a better and trusting mechanic now), replace the drive shaft with an aluminum one and replace the front struts.

Does anyone have a recommended aluminum drive shaft I should get?

 

Hmmmmm I'm wondering if the car is dog tracking from an accident? Do you know what dog tracking is?

 

No sir.

 

its where the front and rear wheels do not travel in line with each other. Probably not your problem. I picked up my alum drive shaft from shaftmasters. Came with a free tshirt everybody makes comments about when I wear it. Try rotating your tires and see if that helps.