GRUWEZ

Last year I replaced the front rotors and pads on my 993 Turbo. The rotors were pretty badly corroded on the inside then, which was basically what made me replace them. The pads were not really on their way out, but with the calipers off, I changed them anyway. While I had the calipers off, I cleaned them and checked the pistons for binding. Everything seemed fine. When all was done, I manually bled the brakes. Then I took the car to a Porsche dealership where they bled the entire system with their machine.

Now, a year later, I noticed that the front rotors start rusting again on the inside. As if the inner pads do not push hard enough against the rotors. To add insult to injury, the rear rotors are now also severely corroded on the inside. The outsides look just fine. So it seems that on both the front and rear rotors, the ouside pads push hard enough against them, but the inside ones don't. For what it is worth, the car seems to brake just fine. It does not pull to one side and the braking force is as strong as ever.

What I did notice is that when I repeatedly press the brake pedal very hard until it hits the floor, after about 10 times, the low brake pressure warning light comes on. It goes out again after a couple of seconds after I have stopped pressing the brake pedal.

Any ideas what I could look for before dropping off my baby at the dealership?

Thanks for your help!

911/Q45

The brake pressure pump just falls behind after that many pumps so close together, no problem there. I'm thinking the calipers have corrosion in the bores, a visual inspection after disassembly seems in order.

Felix

How easy was it to remove and replace the pads? The stainless steel caliper plates can get corrosion underneath them making the pads bind in use and making them difficult to remove and replace. These plates are perpendicular to the faces of the pads and the edges of the pads rest/push on them so as to preserve the softer alloy of the caliper itself.

GRUWEZ

When I did the front rotors, I noticed the problem you mention. But I cleaned up the calipers and the steel plates. Then I installed new pads. Everything seemd fine afterwards. I must admit the car does not see a lot of use (shame on me). During the summer months it basically sits in the garage. Perhaps I should remove all four calipers once again and give them a thorough going over.

Felix

The corrosion usually happens underneath the plates causing them to lift; the plates themselves often don't look too bad.

Also, are you ever really using the brakes hard? Try a few full-on stops from 100 down to 20 in quick succession and see how much corrosion is left on the discs.