01 Cobra Vibration at 85Mph

[sam woodson]

I bought the car in August 07 with 49k miles. It had the vibration then, but I didn't think it was until 100Mph because the speedo was off due to a previous owner changing the rear end to 3.73. After getting the SCT tuner to adjust the speedo, it's annoying at 85Mph.

I can feel it at lower speeds, but I can really start to feel and hear it at 80 and at 85 it causes the mirrors (all 3) to vibrate.

I replaced the drivers side front wheel bearing when I first bought it. There was a noise, and it's now gone. Didn't help the vibration though.

The tires looked almost new, but I have had them balanced twice, no change there either.

I'm trying to isolate the problem. I don't notice any difference in the vibration if I put the clutch in, or even if I put it in neutral and let the clutch out.

Driveshaft?

Another wheel bearing?

Previous owner messed up the 3.73 installation?

Universal joint?

I just had the brakes replaced all around and the rear rotors turned. Just incase, covering all the bases. The car drives great otherwise.

Finally, is the stock 01 Cobra driveshaft Steel or Aluminum? There is a driveshaft shop in town, but they won't work on Aluminum and they don't work on cars, you have to take the driveshaft into them.

Thanks in advance.

 

[ac427cobra]

Couple of things:

Check your u-joints.

Check your diff pinion angle to the driveshaft and compare it to the transmission driveshaft angle. If that's good turn your driveshaft 180 degrees on the pinion flange.

Check the nuts on the halfshafts and torque to 250# with a 36mm socket.

If that doesn't do it check back in.

:thumbsup::coolman::beer:

 

[Sun Devil Cobra]

I had the same problem months ago, and it was the u-joints.

 

[davz]

I have the exact same vibration. As you go faster, it gets more violent. I will be upgrading the halfshafts this week to the 03-04 shafts, so I will be trying everything. I have a pretty new alum driveshaft, so I don't think its the u joints.

Please post what you come up with.

 

[brkntrxn]

Do everything Bruce suggested.

On a similar note, I had similar vibration from 80 or so up til about 110 in my 99 when it had the 4.10s. Now with the 3.55s it is gone. I suspected that the previous gear install was the culprit, but the 4.10s that came out looked perfect. It may have been something else in the install or it could have been the pinion angle.

 

[Hi-Hat]

I had the same thing and it ended up being one of the CV joints in my halfshafts.

 

[davz]

Just upgraded the half shafts to the 03-04 shafts. Nothing fixed. Turned the driveshaft 180 deg and seems to be 90% better.

Oh well, I wanted to upgrade the shafts anyway. Anyone want a pair of good 31 spline shafts out of a '01?

 

[SteveB99]

I had exact same issue when went to 4.10s. Aluminum driveshaft was my cure.

 

[davz]

Bruce, Couldn't figure out how to reply to your PM.

Update: the vibration is still there. I guess I didn't drive the car enough after I did the work. It is better after rotating the driveshaft though.

Sam, have you come up with anything on your car?

 

[davz]

I was talking to a local mechanic, and he suggested the pilot bearing. The prev. owner of my car said he replaced the clutch and put a new pilot bearing in, but maybe it was damaged in the swap.
Has anyone run across this?

 

[Menace-01Cobra]

I had the same problem and it turned out to be the tires not being balanced properly. Proper balance and air pressure are a good place to start.