Clutch Bleeding: No brake fluid flowing, possible master cylinder ?

[tornadored7]

Background:

Car: Golf GT TDI PD 130
Gearbox: 02M.ERF

Car was suffering from the common 02M problem of a non returning clutch pedal, (i.e. a very low biting point, and also after pressing down the clutch pedal it would only return up halfway).
This was always worse when the car was cold, and became less severe after the car was driven for 10/20 minutes.

I struggled with the car like this for a few weeks, but more recently things worsened as gear changes began to become very difficult when first starting the car.

Knowing that the brake fluid in the Clutch/Concentric Slave Cylinder (CSC) is never flushed during a brake fluid change, I planned to suck the old brake fluid from the CSC and follow this with a clutch bleed.

I removed the plastic T piece coupled to the CSC, connected a hand vacuum pump and tried to suck out the old brake fluid. Despite several attempts, only a minimal amount of brake fluid was collected.


Problem:

The real problem then came when reconnecting the T piece to the CSC, then trying to bleed the clutch.
Using a Gunson’s Eezibleed pressurised to 29 psi (2 bar), absolutely no brake fluid emerges when the CSC bleed nipple is opened

Instead of brake fluid trickling from the CSC nipple, it overflows from the brake fluid reservoir, almost suggesting a blockage somewhere in the clutch hydraulics ?



Symptoms:

· Despite using 29 psi of pressure, also manually by cycling the clutch up and down or when applying 20 in hg of vacuum using a vacuum pump, no brake fluid is flowing from the clutch bleed nipple.

· No signs of any brake fluid leakage anywhere (near the clutch pedals, the clutch pipework, the diaphragm valve, the brake fluid reservoir, the clutch flexihose, the T piece, ...)

·Brake fluid level in resevoir remains constant, regardless of whether pedal is pressed or not

· There is clearly air in the hydraulic system, since the clutch pedal drops to the floor and must be manually returned to an up position.

· The ‘blockage’ is at a point before the diaphragm valve, since the pipework after this (including the clutch flexihose) flows brake fluid.
Checked by disconnecting the diaphram valve (round box near the ABS pump), and pushing in a spare CSC that was connected up.

· With a vacuum pump/gauge attached to the pipe where the diaphragm valve normally connects, the vacuum level rises when the clutch pedal is brought up. There is a corresponding decrease in vacuum when the clutch pedal is pushed down

· Likewise, airflow can be heard when lifting/dropping the clutch pedal.



What next ?

1) Does this sound like a fault with the clutch master cylinder (CMC), and what are the definitive symptoms for a worn/faulty CMC (including seals being damaged/having flipped over) ?

2) Is there any way to diagnose CMC issues, either with the CMC in situ or by disconnecting pipes ?

3) Is it worth disconnecting, then reconnecting the CMC to check whether this has any effect ?

4) I have a spare CSC that could be used, if this aids in diagnostics

5) Is it worth getting underneath the car to have a look round, and what/where should I be looking/for ?

6) Any other suggestions please ?