Wheel Spindle Nuts Getting Loose. Why

I have a vintage 1984 Subaru 4wd wagon that I’m fixing up. It has the oddest problem. The front wheel spindle nuts (NOT the lug nuts – the big nut in the middle if the wheel assembly) keep getting loose. I’ll take out the cotter pin and tighten them down to 150 ‘Lbs like the book says and within 500 miles they are loose again. I can’t understand it. How can they get loose if there is a cotter pin in in there? I took the whole wheel – axle assembly and cleaned everything with brake cleaner and made sure the axle shaft was seating all the way but it still loosens. I’m at as loss. Otherwise I have this car running like a champ. I’d like it to be 100%
Additional details. The wheel bearings have about 15K miles on them and this problem only started within the last 5K miles. They do not make noise. The cotter pin is replaced each time the nut is tightened and there is no room for it to move. I did not grease it after I cleaned it and I’m going to take it apart now and apply grease to the cone shaped washer.

Answers for The Question

  1. Pedal2themetal45
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