Noisy Differential
 

The limit slip 3:27 differential in my '97 Cobra seems a bit noisier than I think it should. Last weekend I drained some of the gear oil and replaced it with a tube of friction modifier and topped it off with Mobil 1 synthetic. It seems to have helped a little bit, but is this "grinding" sound normal for these diffs? Someone also recommended going to a parking lot and driving figure 8's to help work in the friction modifier.

It might be the bearings. When I put my gears in, the bearings were all ready wearing. That was after a whopping 8,000 miles on the car. According to my mechanic, that's a common problem for late model Mustangs. Usually it doesn't cause any serious problems till much later in the car's life. 100,000+ miles. But it might be the noise you're hearing. Just a thought.

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'97 Cobra, K&N, Flowmaster, subframes, 4.10 gears, Steeda Tri-Ax shifter, Steeda G-Trac 3, Cobra R wheels w/ Goodyear F1s

Are the bearings easy to change? Also, how do you like your 4:10s? I am thinking about changing mine to 3:73s.

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'97 Cobra, K&N, Rio Red

I love my 4.10s! The first time I floored in 1st from about 5 mph.... It was great. The front end jerked up, the rear tires squealed, and the car took off. A hard 1-2 shift, the rear tires lit up again and back end got really really loose. It was great. Its like a whole new car. Some suspension work, and some bigger stickier tires later, it squeals in 1-2 and 2-3 shifts, but hooks well. Its deffently a worthwhile modification.
As far as miliage: It took a while to re-learn to drive. I use 2nd for 1st most of the time now. Around town I didn't really loose anything. On the Interstate, it runs at 2500 @ 70 mph, and I lost maybe 1 mpg. I get between 22-24 depending on traffic and what not.
I don't know for sure, but I think you have to pull the back end apart to change the bearings, which is a big deal. I changed mine at the same time I did my gears, so it wasn't that much more. I think my mechanic charged me $10 for the bearings and basically nothing for the addition labor. So the bearing by themselves are expensive to change, but if your changing your gears also, its no big deal. Another thing to consider is that I believe their is a recall on '97 Cobras for less then normal sound insolation in the back. Its not a big deal, but it may also account for noise coming from the back end. Compared to my brother-and-law's '94, my car is somewhat noisier in the back.