View Full Version : weird vibrations

08-25-2005, 07:03 PM
hey, i just bought my 99 cobra about a month ago and i have noticed that above 80 m.p.h there is an on and off again vibration. I think it is coming from the driveshaft. My mechanics tell me that the vibration is normal but i think thats B.S.:thumbdwn: :thumbdwn: . My cobra is lowered with eibachs and has 275/35/18 cobra R's. Has anyone else had this problem and if so what did you do to correct it??:scratch: Any help would be appreciated.

08-25-2005, 10:24 PM
get a second opinion first.

08-26-2005, 06:31 AM
The vibration is not normal. Have all of your wheels re-balanced for starters or at least checked. Also there may be a bad yoke on the dirve shaft either at the output shaft of the transmission or at the differential input. If it is an off balance drive shaft you may even feel it slightly at lower speeds. You may even feel it throught the stick shift too. Check the dirve shaft, by this time it should be a bit rusty which is normal for the stock steel shaft. Never paint a drive shaft since that may throw it off balance. Is it possible to find out if there was any work done on the car in relation to the differential or drive shaft (like clutch replacement or rear gear change). If the yokes were not re-assembled properly you may get vibration from that. Also if the previous owner had the rear gear changed it is probable the back lash was not set properly or it was not shimmed right. Then again, it may be a half shaft on its way out. My guess it is tire balance, you may have thrown a weight off a wheel. If they are the same size and type of tire (front and rear) try rotating them to see if the vibration moves to the front.

08-27-2005, 12:56 PM
When I bought the car it had bad tires so I had new ones put on, 4 wheel alignment, checked toe and camber. The car vibrated like this when i bought it and it still does now. I also just had the clutch replaced because the throwout bearing was going bad. U dont notice anything when the car is at any speed below 80. and judging from the rpms, the gear hasnt been changed 2000 at 70 mph. it is an on and off again vibration, it almost seems to pulse. I was thinking since the car was lowered maybe i changed the bend in the driveshaft????

08-28-2005, 02:47 AM
if you have the IRS it would be hard to change the angle of the dirve shaft since the differential is fixed and caged in the IRS frame. The only geometry that will change is the half shafts. It may be the half shaft joints that are vibrating.

I had experienced a simialr issue with my Explorer. The U joints (yokes) needed rebuilding which fixed most of the issues. The cause was an off balance driveshaft which was replaced. The balance was thrown off due to undercoating on the shaft. However, the vibration occured at any speed.