Attention: TDR Forum Junkies 
Nonoffense taken, man. As I said, I've seen it more frequently in differentials which are easily overfilled. This would include the MagHytec covers.
The lube hitting the pinion seal and bearings "pumped" up there by the effect of the gear oil being slung off the ring gear. It's then channeled in the housing to drain back, going over the pinion bearings as a course of gravity feed. This is why you'll starve the pinion bearings if you simply flip the housing. The seal isn't designed to deal with pressure or submersion in gear oil. The oil in this area doesn't sit against it or have any real pressure to it, aside from gravity, in a properly working internal axle system.
The axle seals are designed differently and to handle the effective submersion they see.
Gear oil is resistant to flow, so trying to get the pressure to escape a vent hose in the axle tube that has gear oil covering it can and will cause leaks elsewhere. Often in the weaker pinion seal. If the seal is old or worn from other factors, it will leak that much faster and/or worse.
Any time we do a diff cover with a higher than factory fI'll capacity or on the non-vertical aftermarket housings, we drill and tap a vent into the diff housing and run the hose up from there. I've seen and smelled the effects of overfilled housings many times over the years.
You're right in that many folks don't even realize the vent serves a real purpose and can get clogged over the years. It's a maintenance item to blow it out when changing gear oil (do it with the fill plug off/loose, but oil in the diff to flush it out with the gear oil).
The lube hitting the pinion seal and bearings "pumped" up there by the effect of the gear oil being slung off the ring gear. It's then channeled in the housing to drain back, going over the pinion bearings as a course of gravity feed. This is why you'll starve the pinion bearings if you simply flip the housing. The seal isn't designed to deal with pressure or submersion in gear oil. The oil in this area doesn't sit against it or have any real pressure to it, aside from gravity, in a properly working internal axle system.
The axle seals are designed differently and to handle the effective submersion they see.
Gear oil is resistant to flow, so trying to get the pressure to escape a vent hose in the axle tube that has gear oil covering it can and will cause leaks elsewhere. Often in the weaker pinion seal. If the seal is old or worn from other factors, it will leak that much faster and/or worse.
Any time we do a diff cover with a higher than factory fI'll capacity or on the non-vertical aftermarket housings, we drill and tap a vent into the diff housing and run the hose up from there. I've seen and smelled the effects of overfilled housings many times over the years.
You're right in that many folks don't even realize the vent serves a real purpose and can get clogged over the years. It's a maintenance item to blow it out when changing gear oil (do it with the fill plug off/loose, but oil in the diff to flush it out with the gear oil).
Last edited:
