Nasty Rear End vibration in 03 Cobra, no one can help me!!!

Kdubslugga

Active Member
Jun 7, 2003
1,515
4
38
Akron, OH
Ive got an 03 Cobra with 580 rwhp. I have 19x10 IForged wheels with 305s out back. Went i rip on it full throttle it feels like the read end is moving all over the place almost like a side to side wheel hop. I had my car to Pauls high performance, he replaced a bent rear tie rod that was in the shape of a banana with some aircraft grade tierod, and it did nothing. He said he thinks the wheels are flexing. I contacted the wheel company and he said its impossible, if the wheel flexed it would break. All IRS bushing look and feel solid. Im wondering if it has anything to do with the contact patch due to the large tires and 19x10 inch rims. If i slap the stock rims on with 285s, it drive perfect. This is major issue, its on the verge of losing control when it starts. Any ideas, ever heard of this before?
 
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Sounds like you just have too much slop in the various bushings for high traction tires. Also you need to take it to a better shop, rumor is that shop sucks.

What is the deal with your IRS and diff bushings, are they stock? Does your car have the incorrect IRS bolts that some cars got on the assembly line by mistake? There could be a lot of things wrong or a combination of things. You need to do some research and get under there and check stuff out.
 
Since one set of wheels and tires ride fine and the other set does not, you might check that the wheels and/or tires are out of round - I have personally seen this. To check, put the back end up on jackstands. Using a separate jackstand, put a pointed object, like a pen, on the jackstand right at the wheel lip, as close as you can get. Now, spin the tire (or start it and put the car in first gear at idle) and you can see if the wheel is out of round. Next, same thing for the tire - put the pen right at the outer edge of the tire.

If the wheels/tires check out OK, I would suspect your differential bushings are shot. I had to re-seal my pumpkin last year and I was amazed at how soft those rubber bushings are, especially the rear one. That made for a lot of rear end movement. I replaced mine with poly and it made all the difference as far as movement and "clunk." With your HP levels, I would suspect aluminum would be a better choice - maybe Bruce's FTBR complete set for the IRS.

It could be some other suspension pieces but it would seem they would be bad with either set of wheels/tires on.

Good luck, hope you figure it out.
 
problem

so is your problem a viberation or wheel hop?

the front sub frame bolts should have a 21 mm nut...if yours is an 18mm its wrong....

if wheel hop is your problem than ftb bushing kit is needed

whats normall when stock tires go back on?

different tire tread and sizes mix matched will make a car drive wierd also...