Question about that time I ignored my mechanic's advice on gear oil and cooked my rear diff on I-80

Kai Chen · 2026-10-03T18:25:03.68902+00:00

I used to think gear oil was gear oil, so when my guy Sal at the shop in Reno told me to run 75W-140 in my truck's rear diff for towing, I brushed him off and used the cheaper 80W-90. Two weeks later I was pulling a trailer over Donner Pass and the diff started whining so loud I could hear it over the radio, and by the time I got to Sacramento the fluid was black and full of metal flakes. Cost me $680 for a rebuild, and Sal just shook his head and said "told you so" when I brought it in. Anyone else learn the hard way that the weight on the bottle actually matters for towing?

Vivisector

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Question about that time I ignored my mechanic's advice on gear oil and cooked my rear diff on I-80 | Auto Gear Discussion - Vivisector