Discuss Best rear end gear oil to use (75w90 or 75w140) on AllFordMustangs.com, the place for Mustang enthusiasts.
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Hey guys, I have a 2006 Mustang GT with manual transmission. I had rear end work done a few days ago and ever since, it's groaning in the corners. I'm pretty sure they put 75w90 in the rear with one bottle of friction modifier. Doesn't sound like that was the best choice. Shouldn't I really be running something like Royal Purple 75w140 with at least a bottle of friction modifier? Especially since I now have 3:73 gears. I also don't know if my car has the updated clutch pack from Ford or not but I never had a problem with noise in the corners before (nearly 80,000 miles on the car).
Well, the work I had done was the pinion bearing replaced and the Ford Racing 3:73 gears installed. Right now it's using 75w90 with one bottle of friction modifier. I don't know what that 75w90 is though at this point. Haven't been able to talk to the tech yet today. Problem I'm having is that it groans in the corners now. Never did that before (80,000 miles on it). Short of him opening it back up and going through everything again I'm wondering if its really a fluid issue. Sounds perfect when the rear end is cold but as soon as the rear end warms up I get the groaning and even some gear chatter.