Front End Shaking/Vibrating

I have a 2004 Grand Prix GT1 with about 97,000 miles on it. At highway speeds my front end shakes/vibrates. I can feel it in the steering wheel, at my feet, and both the driver and passenger seats. When I let go of the steering wheel, it shakes horizontally (clockwise and counter clockwise) about a quarter inch or less. It doesn't shake insanely, but it is definately visually noticable. The shaking/vibration seems to get worse when the speed increases and when I accelerate, but more so when I lightly accelerate. If I'm going 70 mph and let off the gas, the shaking/vibration lessens. If I'm going 70 mph and lightly accelerate, the shaking/vibration worsens/increases. I did a road test with a friend today and had him takes notes while we were driving. We both felt it from 40 mph and up. It isn't as noticable under hard acceleration as it is under light acceleration.

It isn't a wheel balance issue because I just had all 4 wheels rotated and balanced. About 6,000 miles ago I had all 4 wheels rotated and balanced because I was noticing it back then. I do have one slightly bent wheel, but the bent wheel has had a chance to be both in the front and the back. I have also had the tie rods, front wheel bearings, and intermediate shaft replaced since I have owned the car (I bought it 53,000 miles ago).

Is it a tire issue? I did the quarter test and on the outer sides of the tires the tread comes up to Washington's head. In the middle of the tire the tread comes up past his head. I assume that's fine. I did get the tires 50,000 miles ago. Time for new ones or is the tread fine? My mechanic hasn't mentioned any signs of uneven wear except for the tire on the slightly bent wheel. He says it looks like someone hopped a curb at one time. Probably my girlfriend, haha.

I did see something on the internet about GM 3.8L vehicles having problems with the CV shaft and it causing shaking/vibrating at highway speeds and under acceleration. Is this common for our Grand Prixs too? Could this be the culprit?

I did pop the hood and looked at the engine. It doesn't look like it is a motor mount issue. The motor barely moves when the car is in nuetral and gas is given to it. When shifted into drive or reverse, it looks normal. Also, I don't think it's an allignment issue because the car tracks straight while going down the road.

If you guys can give me some help, information, tips it would be greatly appreciated! I have a 100,000 mile bumper to bumper warranty and I would like to get this issue fixed before the warranty runs out. Thanks guys!

I would guess the tires with the mileage you have on them. The tread could be fine but the internal belts have shifted or broken. But you say you have rotated the tires front to back and the vibe is still there so the cv/half shafts are the likely culprits.

Originally Posted by WhatNext

I would guess the tires with the mileage you have on them. The tread could be fine but the internal belts have shifted or broken. But you say you have rotated the tires front to back and the vibe is still there so the cv/half shafts are the likely culprits.

The tires I have are Goodyear Assurance Comfortreds. They are warrantied to 80,000 miles, but personally I think that's a joke. From what I'm seeing on the web, 50,000 miles of use is pretty good for these tires. Any experience with these tires?

You have a broken belt in one of the front tires. The people who balanced your tires should have seen it.

Yea i also have this issue. Have yet to get it balanced or checked out.

Same issue with mine but I replaced the tires two weeks ago. Going into the shop on Saturday to get the CV/half shaft checked.

Sounds like the syptoms I had with my bad cv shaft.

1. 40 and up
2. worse the faster i went
3. almost non existent under deaccleration
4. worse at a part throttle accleration

I think you need to change the CV and that is not cheap have a look on ebay or autoparts online store so you can already canvas for parts.

What do you mean not cheap? CV axles are one of the cheapest parts on these cars... $50 a pop at Auto Zone or Advance. Just replaced mine 2 weeks ago. Wheel bearings on the other hand, those are about $90.

Theres a reason those axles were so cheap...

yes, but since autozone cv's are lifetime warranty, you just take them back and since they break first, it might protect ur tranny from gernading....

UPDATE - Took my car to my mechanic and he found out what the problem is. It is the CV shafts. Going to get both of them replaced now. Thanks for the responses.

Yup, Lifetime warranty. Axles are easy in and out, I'll gladly pay $50 with lifetime warranty and when i grenade one take it in and get a new one for free..

Originally Posted by BoostenGTP02

What do you mean not cheap? CV axles are one of the cheapest parts on these cars... $50 a pop at Auto Zone or Advance. Just replaced mine 2 weeks ago. Wheel bearings on the other hand, those are about $90.

you are right about the bearing, just had mines done because am having the same issues with my front wheel, after reading these post i will have my cvs check this week..