So here's the breakdown.
I purchased a completely stock 1997 cobra with 104k miles on it in January of 2015. I'm driving it around for sometime like this with no problems other than a constant whining sound between 40-80mph. My friend at work was constantly wanting to race. So, on the way to Race Wars I indulge. Everything's going fine up until about 110 mph+. Once I get to this, I get a vibration/rattling noise in the back. When I say rattling, I really mean clunking/rattling. With this in the back of my mind, a constant whining noise from the rear, and the rear rattling/clunking when decelerating (very pronounced when decelerating in nuetral), I decided to pull the trigger and rebuild the rear end and throw in some 4.10's while I'm at it.
During disassembly I noticed that my upper passenger control arm is shot. Of course I thought, "This has to be the cause of the vibration". So, I decided I will replace all of the control arms as well as the bushings on the diff.
Specs on rear diff:
Pinion Bearing Preload w/ all new bearings ~29-30 in/lbs (I know this is pretty high, but I researched that new bearings get much higher preload and will eventually slack up on this preload the more you drive)
Backlash ~ .0012
Wear pattern ~ sat nearly in middle on accel and decel sides. The pattern sat slightly inward in reference to the rear diff of where the centerline would be.
After I finish buttoning everything up I decide to go for a drive. WOW! It drives incredible...but that was last week. This week, however, I am getting that clunking/vibration from the rear again, however, it is at 90mph +.
I am kind of confident that it may be the driveshaft is out of balance and the new gears + new control arms are making the vibrations/clunking more pronounced.
I have researched the web and they all say an aluminum driveshaft will clear up the vibration, but they didn't say anything about a clunking sound. Should I look into getting an aftermarket aluminum driveshaft simply to remedy the problem or should I be more worried about having to redo the rear? I'm not sure the rebuilt rear diff is the problem because this was a pre-existing problem, but it's more pronounced now at slower speeds. It's nearly at the point to where I feel the rear end will blow up and I'm worried about going over 80mph.
I purchased a completely stock 1997 cobra with 104k miles on it in January of 2015. I'm driving it around for sometime like this with no problems other than a constant whining sound between 40-80mph. My friend at work was constantly wanting to race. So, on the way to Race Wars I indulge. Everything's going fine up until about 110 mph+. Once I get to this, I get a vibration/rattling noise in the back. When I say rattling, I really mean clunking/rattling. With this in the back of my mind, a constant whining noise from the rear, and the rear rattling/clunking when decelerating (very pronounced when decelerating in nuetral), I decided to pull the trigger and rebuild the rear end and throw in some 4.10's while I'm at it.
During disassembly I noticed that my upper passenger control arm is shot. Of course I thought, "This has to be the cause of the vibration". So, I decided I will replace all of the control arms as well as the bushings on the diff.
Specs on rear diff:
Pinion Bearing Preload w/ all new bearings ~29-30 in/lbs (I know this is pretty high, but I researched that new bearings get much higher preload and will eventually slack up on this preload the more you drive)
Backlash ~ .0012
Wear pattern ~ sat nearly in middle on accel and decel sides. The pattern sat slightly inward in reference to the rear diff of where the centerline would be.
After I finish buttoning everything up I decide to go for a drive. WOW! It drives incredible...but that was last week. This week, however, I am getting that clunking/vibration from the rear again, however, it is at 90mph +.
I am kind of confident that it may be the driveshaft is out of balance and the new gears + new control arms are making the vibrations/clunking more pronounced.
I have researched the web and they all say an aluminum driveshaft will clear up the vibration, but they didn't say anything about a clunking sound. Should I look into getting an aftermarket aluminum driveshaft simply to remedy the problem or should I be more worried about having to redo the rear? I'm not sure the rebuilt rear diff is the problem because this was a pre-existing problem, but it's more pronounced now at slower speeds. It's nearly at the point to where I feel the rear end will blow up and I'm worried about going over 80mph.
Last edited:
