Please help if you have knowledge on gear oil &/or 9" rears. I have a 3.50 geared OPEN 28 spline 9" rear with a POWER TRAX unit in it. When first installed the PowerTrax unit was fairly quiet but after several thousand miles it started making clicking noises after the gear lube is warmed up. I noticed noise at low speed in coast or under light power. I called the tech department and they said sounds normal as long as the unit works like it is supposed to (which it does) and I could run ANY gear oil I wanted with it. Since I only noticed the annoying clicking after the fluid was warmed up I figured I would suck out the old 75w90 full synthetic gear oil and put in some 75w140 FULL SYNTHETIC so it would be thicker when warm and stop the clicking. I did this today and sure enough the clicking started to show up in 10 miles and then after it got a bit warmer it went away and is quiet just like I want it. PERFECT!!! But here is the question --- Ford originally called for straight 90 weight hypoid gear oil in this rear end - will this thicker gear oil screw it up? It is a high mileage unit from a early 70's late 60's BRONCO but has no strange noises and a good gear mesh pattern. Thanks in advance!
Gear oil question 75w140 FULL SYNTHETIC in early 70's 9" conventional rear
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