Update by David S. Wallens to the
Porsche 911 Carrera project car
Feb 7, 2025
|
Porsche,
Restoration,
Porsche 911 Carrera,
Warped Rotors,
Brake Vibrations
Photography by David S. Wallens
Womp, womp, womp, womp.
The Porsche needed new brakes.
We could feel it when coming to a stop–warped rotors, many would say.
But not quite. Technically “warped rotors” are not warped. They do not resemble potato chips.
Let’s quote what longtime brake engineer James Walker Jr. wrote in Grassroots Motorsports:
“In nearly every single case, warped rotors are not physically warped at all. The common misconception is that the rotors get hot enough to distort and then, upon cooling, end up looking like a pretzel. Contrary to popular belief, rotors simply do not warp in this fashion.
“The vibration that is felt in the steering wheel and floorboard is almost always caused by rotor thickness variation, also known as TV, and the physical pulsing in the brake pedal is nearly always a direct result of the caliper piston extending and retracting as it tries to follow a rotor of varying surface thickness.”
[How to prevent brake vibrations]
Could we save our rotors? Maybe? How about, instead, if we freshen everything back to new: pads, lines and rotors that haven’t been cut and no longer have rusty centers.
When it comes to brakes for our 1984 Porsche 911 Carrera, two options exist: stock or modified.
And if going modified, that opens up many options, including Wilwood’s big-brake kits.
For this car, though, we wanted to keep it stock–or really close. It’s not a track car, and we haven’t found the stock brakes lacking in capacity. They just needed a refresh. We also wanted to keep the car looking stock, with any mods, like our Yokohama A008P tires, falling under the heading of period correct.
[Brake fade: What you need to know and how to fix it]
Rotors? OE-style replacements. No slots, no holes. Ours came from Dynamic Friction.
Pads? Textar O.E. replacement. Autobahn Daytona, our local Porsche shop, favors this brand.
Brake lines? Goodridge braided. We’ve been running braided brake lines on our cars for years: slightly firmer pedal plus better defense against hazards. The least expensive option for OE-style rubber lines from Pelican Parts retails for about $85 front and rear. Braided? About $125 complete from Pelican Parts; we paid a few bucks less for Goodridge lines from Tire Rack.
Brake fluid? Motul RFB 600 Factory Line. Why this one? It nicely balances dry boiling point (594 degrees Fahrenheit), wet boiling point (401 degrees) and price (about $20 per 500mL bottle, although deals exist on two-packs.)
[How do brake fluids compare? | Buyer's Guide]
While going through the brakes, Autobahn Daytona noticed that the front pistons had, at some point, be incorrectly installed. A call to Worldpac had rebuild kits on the way.
End result? Brakes that feel back to stock: no pulsing, no noises, no nothing. And, to most onlookers, the brakes look stock, too.
Workd my way part way through university in a shop that turned rotors. True them up in the lather using a dial indicator and shave a bit off and end up in proper balance. Very few were actually warped, they just had worn areas. I guess if you were driving a heavy load down Pike's Peak you might build up enough heat to actually warp one when you drove into the snow.
In reply to wspohn :
So where did the term warped come from? I can see why people think they’re actually warped, though.
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