Front Diff Oil

[bill monahan]

Here's a question for you guys. I have a sizable leak at my right front steering knuckle. It's oil, not grease so I most likely have a bad inner axle seal. I know I should get in there and change because it might start to wash out grease from the knuckle. Now here"s the question. I just put lock out hubs on and if they are in 4X2 and the truck will NEVER be in four wheel drive, the axles, side gears, ring and pinion and driveshaft will never rotate. Why do I even need a diff full of oil ? Hey, no oil, no leak, hee.

[w30bob]

Hi Bill,

Wow...that's some question! I'm not that familiar with the M37 drivetrain, but here's a few things to consider. On most 4WD systems, even if the front diff is not in gear there is parasitic drag that makes the internals rotate. But even assuming the front diff doesn't rotate at all when disengaged.......without lube the seals in the system will dry out. And there's the bigger factor of Murphy's Law that says even though you NEVER intend to use it in 4WD.....you inevitably will find yourself needing to at some point. And I for one would never rely on my crappy memory to tell me not to push that lever if I needed to. Cuz if you ever do....and there's no lube in the diff.....you're going to stop moving permanently pretty fast.

If folks on here can confirm that the front diff doesn't rotate at all when disengaged.....and you really want to run it dry.....I'd make sure to remove the driveshaft. I'm looking forward to hear what folks have to say about this question......thanks Bill.

regards,
bob

[bill monahan]

Thanks Bob, I don't plan on leaving it dry permanently. Just a thoughtful question. Jacked up truck and with hubs unlocked spinning the wheels results in no driveshaft movement.

[milstencil]

Bill,
Have you checked the differential vent? That little sucker has a habit of
getting plugged up, and if it does the differential will build up pressure and
blow the oil out the seals. All 3 of mine were plugged and resulted in a lot of leaks.
Check the easy stuff first. Take it out and clean with carb cleaner and blow out with air.
Rick

[bill monahan]

That's a good tip Rick, gonna check.

[MSeriesRebuild]

Go through the entire front axle to include steering knuckles. Do it right using good parts, not NOS junk or leather seals. Put the best quality grease in the knuckles so the oil doesn't bleed from the grease, otherwise the oil will separate from cheap grease and the drip will keep right on coming at the knuckle seals.

Running with the front diff dry is not at all smart, condensation will cause interior rust and pitting will ruin every gear and bearing in short order with no protection. Even if it is an established fact that front wheel drive will never be needed, if you don't keep it filled with premium quality oil, and engage it periodically to keep everything oiled up, it will be destroyed from within as a result. A rebuild can without a doubt be a major expenditure, but honestly, there are no short cuts that work, there is no substitute for doing it right, doing it once, and then enjoy trouble free service for many years to come.