To many the manual shift 928 is the highly desired model. The clutch system for the manual shift is hydraulically operated. The source of the fluid is the brake master cylinder reservoir. A hose from the brake master cylinder transfers the fluid to the clutch master cylinder.
My manual shift Porsche 1979 928 diagnostic warning light flashed “brake fluid” when I turned on the ignition switch. I did see a puddle of something underneath the car. I popped the hood and observed that the hose that furnishes brake fluid from the reservoir to the clutch master cylinder was seeping fluid. It had drained enough brake fluid from the reservoir to trigger the warning light. I refilled the reservoir, double checked that the brakes worked properly and drove to my Porsche mechanic, Dan at Exotic Motorwerks for repair.
The brake fluid hose is labeled 29 in the diagram above.
It is a difficult and time consuming job because to remove the old clutch slave master hose the entire brake master cylinder and booster must be removed.
The brake pressure regulating valves must also be removed.
The clutch pedal linkage must also be disconnected. Once all the items are removed, only then can be clutch master cylinder be accessed.
In the photo above, the hole in the firewall is where the power brake booster is located.
Porsche Hydraulic Fluid Hose Part Number 999 181 021 50
There is not much more work at this point to replace the clutch master cylinder if needed.
Following reconnecting everything, the brakes and clutch master/slave need to be bled to remove any air in the system.