ZF25 transmission oil pressurised

[alctel]

Hi,

Bit of a weird question, I am getting some weird noise under power and trying to figure out what it is.

One thing is that the gearbox oil is 'pressurised', i.e when i unscrew the dipstick there is an audible hiss sound as it depressurises. Considering there is a breather valve on the transmission, I would like to know if this is normal - I don't remember it happening before!

Thanks for any help

[FPNC]

Some breathers have a ball and spring check valve built in. This can create a bit case pressure. Either way, it has no effect on the operation of the transmission.