I am new to this club and I really hope that I can get some much needed information and assistance. I have a 1983 928 S (right Hand Drive) and observed the following when I used my car on the last 2 occasions.
On the first occasion, I drove the car and the brakes worked quite fine until after about an hour of driving, I lost brake pressure and the Brake (Pr) Light came on. I safely got to my destination which was right around the street when it happened. I stayed for the day and in the afternoon when I was ready to leave surprisingly the brake pressure was good and I was able to drive home safely. I checked the brake fluid level and it was good.
On the second occasion, once again the brakes worked fine but after an hour of driving I lost brake pressure yet again.
I am not sure how best to approach this problem. Any assistance will be greatly appreciated and thanks for any help in advance.
I first suggest that you have the brake system fluid flushed. Porsche service recommends flushing the system every two years. Most owners do not flush so often and find braking failure on the road or during track sessions. Most shops have pressure systems which do a good job of flushing without having to pump the brakes.
Brake fluids are hygroscopic (water absorbing). After years the concentration of water in the fluid becomes great enough that it will boil from the heat generated during braking and when it does pressure is lost and the pedal will sink to the floor! You don't want that.
If a brake flush doesn't cure the problem the brake master cylinder may need to be replaced. This is needed if the pedal sinks to the floor or there is a different between the pressure in the two brake circuits, the warning lamp will illuminate.
Please look into this quickly, the condition is very unsafe!