Hydraulic Transmission Mystery

[Graham Harry]

I have a 2012 Yaris. I am having difficulty diagnosing a problem. I am having difficulty getting into gear. There seems to be air getting into the clutch system BUT there is no indication of where. The fluid level is good and the master cylinder is good. There are no puddles or leaks evident. The garage is at a loss at what to do. When it is bled it is okay for a day or 2 and then it gradually comes back to total non use after 2 weeks. Anyone help? 

[mrfixer]

Very likely to be a poor master cylinder seal allowing air in.  But before you replace it you should check that the vent hole in the M/C cap is not blocked - that will cause air to be drawn in past the seal.

[Graham Harry]

On 5/26/2019 at 12:48 AM, mrfixer said:

Very likely to be a poor master cylinder seal allowing air in.  But before you replace it you should check that the vent hole in the M/C cap is not blocked - that will cause air to be drawn in past the seal.

Thank you MrFixer. I have passed this onto my mechanic. 

[Mike J.]

I assume the fluid level remains the same. How do you know the M/C is OK? If the seals are worn, they may let fluid pass, reducing flow to the slave. Also, was it bled using vacuum or pressure devices? My car has to be bled via the old school two person method: one on the clutch pedal and one at the bleed nipple, monitoring air and fluid flow.

[Bomber209]

Hi, I had a similar problem years ago on a Range Rover. It turned out to be the flex hose in the system, the side walls had weakened and bulged every time I pressed the clutch pedal.

[Graham Harry]

4 hours ago, Mike J. said:

I assume the fluid level remains the same. How do you know the M/C is OK? If the seals are worn, they may let fluid pass, reducing flow to the slave. Also, was it bled using vacuum or pressure devices? My car has to be bled via the old school two person method: one on the clutch pedal and one at the bleed nipple, monitoring air and fluid flow.

The fluid level remains the same. The garage rung Toyota and they said that they have only had to replace one master cylinder on that model so it is unlikely it's the MC but obviously not impossible.