Several things can cause this excessive pressure:
* Overfilled differential: This is the most common cause. Too much oil has nowhere to go when it heats up and expands, forcing it out the vent.
* Internal damage: Worn gears, a broken axle seal (though that would often leak oil elsewhere first), or other internal components generating excessive friction can generate heat, leading to increased pressure.
* Clogged vent: Ironically, a blocked vent can also cause this. If the vent is restricted, the pressure has no way to escape except by forcing oil out through any available opening, potentially including the seals.
* Extreme temperature changes: Rapid temperature fluctuations can cause significant pressure changes within the differential, especially if the oil is already near its operating limit.
In short: The vent hose isn't the problem; it's a symptom. You need to investigate *why* the pressure inside the differential is so high. Start by checking the differential fluid level. If it's overfilled, drain the excess. If it's not overfilled, or if the problem persists after draining excess fluid, you'll need a more thorough inspection, potentially requiring a mechanic to diagnose the issue.
