I'm getting ready to replace pinion oil seals in two differentials. The first is from a 1960 Ford F-100. The pinion gear housing actually unbolts from the axle with no other gears attached, so the preload can be easily set off of the vehicle. I went to measure the rotating friction of the pinion using an lb-in beam torque wrench, but there is no measurable friction. I can spin it easily with my hand and the shop manual says it's supposed to have 8-12 lb-in of friction for used bearings. So, I guess this means that the bearings are just worn to the point that there was no longer any friction left and I should install a new crush sleeve and then tighten the pinion nut until I get 8-12 lb-in of friction.

The second one is from my 1980 W116 300SD (the same 3.07 type that's in a W123 300D or W126 300SD). I have the differential removed from the vehicle, axle shafts off, and drained of oil. I measured the friction and got 25ncm/0.25nm/2.2 lb-in (which is almost nothing). The factory service manual states that used bearings should have 50-100ncm of friction WITHOUT the gear set installed. So, apparently the friction of the pinion of my differential is only half (or less) than what it should be, and that's with the added friction of the gear set that's not supposed to be installed.


I guess this means that wear of the bearings has caused there to not be enough preload on the bearings and I can't use that as a point of reference when I reset the preload. I'd be happy to remove the gear set so I can set the preload to factory specs, but it appears I'd have to spread the case with a spreader which I don't have and then it might cause even bigger problems.

I'm thinking I should probably set the friction to the high end of the specs indicated without the gear set installed (which is 100ncm), since I don't have any point of reference for what it should be with the gear set installed since mine was too low. At least the setting will be better than it was before, and even if it potentially might not have as much preload as it should, I'll at least know it's not too tight, yet tighter than it WAS.

Also, I wish I could replace the crush spacer, but it appears the nose bearing won't come out with the pinion still in place, and once again I don't want to pull out the gear set if it requires a special spreader tool and a bunch of other difficulties.

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1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 350,000+ Miles