@Jody Treadway diff question: driving my truck today I get a metallic "whirling" sound when in 1st gear, 3500+ RPM and off the throttle coming from behind the cab. It does it a little bit in 2nd same RPM also off throttle. I am running my spare driveshaft and the u joints felt ok and I just greased evreything. So do I have a failing pinion bearing, driveshaft center bearing or u joint? Im going to drain the diff fluid tonight and see what it looks like. Is there anyway to diagnose the pinion bearing without dropping the 3rd, this is on an fj80 9.5 diff?
Trying to figure out how many late nights I'm going to be pulling before leaving to wheel later this week lol.
Doesnt have to be Jody, anyone else can let me know what ya think!