mkhargrove

I had pulsations in my front brakes. I pulled the discs and brushed/sanded off the rust from the disc and the hub. Does anyone know of a way to prevent it from returning?

Mrmerlin

I put a lite coating of white grease on the hub face,
otherwise replace the rotors with Zimmerman E coat

mkhargrove

thx!

h2pmr

Petza914

I now only buy rotors with the zinc e-coating treatment on them. Keeps the rotor hats and the vanes in the rotor vents from rusting. Any rotors I've had to use without an e-coat available, I actually masked off the rotor pad surface and painted them myself with high-temp paint. Nothing looks worse through a nice wheel than a rusty rotor hub.

Ultimate solution is Porsche carbon ceramic brakes which I have on 2 of my Porsches, but not available for the 928, though someone could probably retrofit them, making the brakes worth more than many of the 928s on the road LOL

mkhargrove

I don't know if many people pay much attention to the area of contact between the hubs and the rotors, but it doesn't take much in that area to cause vibration in the brakes.

dr bob

Once it's clean, wire brush and grease-free clean, you can spray it with any of several "instant cold galvanize" products. I've been using one by CRC since the boating period, with excellent results. Do the hats inside and out, and spray the finned areas between the friction faces too, for appearance if nothing else. Follow the directions on the spray can, and you should be happy with the results. I primed and painted over the zinc on the outer surface of the hats, using some handy Duplicolor "wheel silver" in a spray can from the POLAPS. I shot a few thin coats of clear to protect the silver, and it looks great with my matching-silver wheels. Take a look at the "before" and "after" pics, taken as part of a larger brake system refurb project effort. You can see the effect directly on the fins and rotor edges; much nicer and cleaner than the original look.

PorKen

Cold galvanizing spray looked to be the factory method for initial assembly on my (40K mile) '80


Rotor hat, axle, flange, and nut on the rear axle (note red assembly mark over paint on axle)


Rotor hat only on the front axle

dr bob

At manufacturing time, dip galvanizing is easier and cheaper than the spray product, and is generally more physically durable. As far as corrosion protection, the spray is just as good. Adding the paint coating over the physically exposed/visually sensitive sections keeps it relatively durable. Looking at the dates on my pictures, it's been about eight years since I did all that refreshing. Still looks pretty new. The blanchard-grinding marks on the friction faces have been buffed off by the brake pads though.

So far the discussion has been about only half of the OP's questions though. The pulsing-pedal syndrome is still open. In my limited experience with such things, three possible causes: Rotor runout, which is pretty easily checked with a dial indicator. Same dial indicator you use to verify crankshaft float/endplay. There's discussion about rotors warping unevenly, something that could be detected with a micrometer and multiple thickness measurements around the rotor friction surfaces.

Last but certainly the most popular cause is uneven pad deposits on the rotor faces, along with rust/corrosion there. Either will cause the rotor to be thicker in some places, pushing back on the pedal. Uneven pad deposits happen when you roll to a stop with hot brakes, and keep the pedal mashed down hard as things cool. The practical solution is to go through the whole pad re-bedding procedure as if they are new. A few hard stops from speed to heat them up, but don't come to a complete stop between efforts. Keeping this from happening again is as simple as adjusting your pedal technique a bit in traffic -- let off the pedal some as you roll slowly to a final stop, just dragging the pads lightly on the rotor faces. Keep only the gentle pressure on the pedal while stopped, so you aren't transferring as much rotor heat into the pads. That way less pad material is transferred locally to the rotor faces where they are clamped. For the surface corrosion problem, most of that seems to come from washing the car and putting the brakes away wet. Water is trapped between the pads and rotor face, and takes a while to evaporate. Do the brakes a favor and go do a lap of the neighborhood after you wash, with the pedal held down enough for the pads to drag. This makes enough heat to dry everything out before you put your baby to bed. In a related note, cold water on a hot rotor is about the only way you will actually warp a 928 rotor short of overheating them on the track. If you are in the habit of washing the car immediately after a drive, might be a good idea to adjust that habit a bit. At least enough to allow the brakes to cool off before you attack with the hose.

Strosek Ultra

Dr. Bob Quote: " For the surface corrosion problem, most of that seems to come from washing the car and putting the brakes away wet. Water is trapped between the pads and rotor face, and takes a while to evaporate. Do the brakes a favor and go do a lap of the neighborhood after you wash, with the pedal held down enough for the pads to drag. This makes enough heat to dry everything out before you put your baby to bed."

That is absolutely correct, I never put away any of my cars with "wet" brakes after washing. After a car wash always drive the car for a short distance and use the brakes to dry up the rotors and the pads.
Åke

Eplebnista

Never wash hard and put away wet.

khalloudy

I have had the same rotors and pads on my S4 since maybe about 2009. Original Porsche. No rust and brakes still in great shape. After about 10k (km) and 10 years. Nothing beats OEM for such parts and worth every dime.