I have a 98 tacoma (~180K) which makes this quiet noise “phoosh”/ air being softly let out when I put the cluch in and while the motor is still cold but running. I mainly hear it in 1st or 2nd gear as I put the cluch in but not while the cluch is fully engaged. the noise also goes away once the motor is warmed up or if I drive the truck later in the day. the clutch seems to engage in all gears in the normal range (for the truck) i.e. about half way down to the floor, and it does not slip out of gear or have trouble going into gear. any ideas? thanks.
First, have you kept an eye on the fluid level in the clutch master cylinder? If not, check that. If the fluid level is low, look under the dash where the clutch pedal rod pass through the firewall to make sure fluid isn’t running down the inside of the firewall. If there is, you need a new clutch master cylinder.
If the fluid level is fine, then what you might be hearing is the cup seals inside the master cylinder beginning to by-pass fluid. These seals are what provide the hydraulic pressure to the system. As they wear out, along with the master cylinder bore, they can begin to by-pass fluid where a whooshing noise can be heard. And as these components wear out, temperature has an effect where the problem is more promonent when the components are cold.
sounds goood, I will check those areas out- on thing though- someone mentioned to me the slave cylinder may make a similar sound- how can I check each of these cylinders out if there is no fluid running out (scenario 1)?