Diff breathers need to be two way not one way valves
If air can only get out when hot then what happens when it cools down?
That is why they are called breathers.
Not my comments below just some crazy person.
Where raised breathers become important, is when you’re trundling along with the short-stick locked in causing everything in your driveline to heat up. Wheel bearings, axles, CVs, diff centres, pinions – the works. As the air in your diff housings heats up, it expands, and pressurises the diff. The breather lets it release this pressure out into the atmosphere, instead of out via your axle seals.
So far, so good. So why would you want raised diff breathers? Because invariably, there’s going to be a water crossing, river, or boat ramp that you’ll want encounter during your travels. If you’re anything like me, you’re not going to want to sit there for hours waiting for your driveline to cool down before you get your hubs wet. As we said before, when the driveline gets hot, it vents air out. When it cools down, it sucks air back in. If your diffs are hot and the breather goes underwater, it is going to suck litres of water through the breather. In some cases, breathers have a one-way valve that closes when the pressure flips. In this case that water can be sucked in through your axle or pinion seals.
