I'm want to know how many of you 4th gen owners changed from the 3.23's to 3.73's in your 7.5 inch 10 bolts? Out of that, how many of you had a bad coast howl when you testdrove after the swap? I work in a drivetrain shop and rebuild diff's for a living. What I am running into is a rash of noisey 3.73 gear swaps. All in cars which had 3.21-3.23's and went to 3.73's. on both 2 cut and 5 cut gears. The setups were perfect and patterened out right. but, on the testdrive, the first time you let off the throttle it howls. There are three seperate cars, An 06 stang GT, an 06 Roush, and most recently a LS1 T/A. These were the only cars I regeared, the rest were Jeeps or Trucks, some of which got 3.73's without incident. I have only gotten the noise out of these three cars. The only common denomiator is the gear ratio's, automatics, and aluminum driveshafts. Aluminum shafts do amplify drivline noise, but, there was very, very little howlbefore the swap on the T/A and one stang had 5k on the clock and the other was about 7k, both were quiet before. The GT got its orig. 3.21's put back in and was quiet. Chew on this and maybe let me know if this might be a common issue.

 

thats not good news to hear, i was thinking about 3.73s i really want to hear if ppl have this problem..