Rotor Minumum Thickness
Exactly which book does one have to buy to know that (for instance)
if the brake rotors are down to this thickness, they need to be replaced?
Please don't say this info is only available in the $hop Manuals.
I replaced my rotors (all four) many years ago. There are clues to tell if they need to be replaced. The best way is to "mic" them. Another way is to measure the prominance the lip along the outer edge. If it is about an 1/8th" deep, it's time for new ones. Also, if there are large surface cracks on the rotor surface, then they may need to be replaced. If that is the case, you may also have a sticking caliper piston(s). Pre 86.5 have two per caliper. 86.5 and younger have four.
If they are OEM rotors, the minimum wear limit is stamped on the hat of
the rotor. YMMV.
~ Merry motoring ~
The minimum thickness is stamped on each rotor -- in that way machine shops can not feign ignorance and machine the rotors below the minimum recommended thickness it is visible right on the part . I believe the early tech spec books up to 1989 have been discontinued by Porsche never to be seen again. The 90-93 is available , now.
A great deal of this type if info is available in the Technical Reference
Booklets, which are about $335 cheaper than the Shop Manuals.
By the way, the answer is 30.6 mm front, 22.6 mm rear.
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