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98cobra1
11-06-2008, 05:36 AM
Hey i need help!! I have been a mustang owner for years and I purchased a 2004 cobra convertable with 6400 miles on it in May. the car bringing it home from new york had a bad vibration at 60 and up. owner said probably flat spot and he would pay for tires. Once home we discovered possible previous damage to the front end as the control arm pass side and kmember were moved 1/2 inch back and control arm bent. lamatta performance here in Orlando has exausted efforts to find it??? We have first check frame it is straight put new springs,shocks,front control arms, new cat back,strut tower brace,full length sub frame connectors, alignment, new tires,changed wheels from one that was ok,rebalanced drivshaft and swaped out the intire IRS from a donan car and no change??? The car drives straight as an arrow and has very slight vib at 55 to 60 and at 62 to 68 shacks you brains out and then settles out at 70 to mild vib until 80 and then is not to noticable. Please if you have any ideas let me know. thanks for your help Cobra98
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totenkopf13
11-06-2008, 06:58 PM
Hopefully, someone on here will have some insight. Seems you have run through most of what one might think would cause such. I have no idea. :dunno:

cobrabitn
11-06-2008, 08:07 PM
You need a competent shop that can find the vibration but I would first check the following:

1. U-joints & bearings.

2. Your driveshaft is warped and even though you may have balanced it, if it is "out of round" it will vibrate at certain speeds.

3. Your driveshaft is not indexed properly, you will need a good shop to properly index your driveshaft. If your car is lowered, you changed the angle of which the shaft has with the transmission.

4. Your tires need balancing or have a broken belt inside of them.

Check these three items and most likely your vibration will be gone.

98cobra1
11-07-2008, 05:53 AM
Thanks Tires have been swaped from my 98 cobra no change but I will talk to the driveshaft shop to see if they checked to make sure it was perfectly round and indexing. Thanks 98cobra

cfradam
11-07-2008, 06:26 PM
Jakes a good guy to have work on your car.I had the same thing happen to my 95 gt.I also did most of the things you did to find the problem.after months of beating my head on a rock and swiping the magnetic strip off the back of my credit card it turned out to be a bad u joint.just make sure that you check the small stuff twice before throwing a lot of money out the window.
ball joints,tie rod ends,poor rack bushings,excessive pinion angle,and u joints will all give these symptoms.
good luck

Adam

98cobra1
11-08-2008, 07:14 AM
Adam yes Jake is the best and has been a friend for nearly 13 years. He is finishing my 92 GT Monday. I will relook at the small things also. I took the driveshaft to advanced driveline so I would hope that they looked at all issues but I will call them today to make sure. We took a donan shaft out of a car at Jakes shop and it still vibrated so not sure about the driveshaft. I also am having a friend set up a camera to video the car under neath to see if we can see it as it starts to happen. Thanks everyone for your help. John

9Cobra9
11-09-2008, 03:50 PM
Idon't know what to tell ya i have heard where people have vibration problems out of the 03-04 cobras. I think i found somethin on either SVTP or SVTOA it was one of the two

cfradam
11-09-2008, 09:31 PM
advanced driveline is also top notch and could be trusted to not overlook anything.the only other thing I can think of is that my balancer started to seporate and made a big vibration.the only thing was that it usually comes apart quick with litle notice.just something else to look at

COBRA_ESQ
11-10-2008, 11:56 PM
There is a TSB for vibrating driveshafts in 2003 Cobras. Do not know if it included 2004.

If it was not for the front end damage I would say that is almost definitely it.
Mine started at 55mph and smoothed out at about 70mph. Replacement driveshaft took care of it. I have also been told that if you remove the drive shaft to mark the universals so it goes in the same way it came out.

puzzle13
11-11-2008, 12:13 AM
I have a 2003 Cobra Convertible that I bought new and it has a slight vibration from 55 - 60. Ford could never get it out totally with replacing & rebalancing tires. This car now has StopTec brakes, MM K-member, MM Coil Arms, MM Coil overs, MM Full lenght subframes, MM Strut tower brace, Diff Brace, all new bushings in the rear, and it still has the vibration. The rear end is off 1/2" on the rear drivers side ... I have to run a 1/2" spacer on that side only! I drive this car at the track and on the street and have never found the problem.

ausie
05-22-2009, 08:21 AM
My thoughts: you mentioned that the K-member was moved or damage previously. I would either replace the K-member if you have not done so. Motor mounts may be bent or engine/transmission is out of the center line. Vibration may be due to engine alignment to the drive shaft.