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Therein Lies the Hub

To wit: This is exactly the wrong front hub/rotor for a 1974 Porsche 914, or any model post-1972.  That fact escaped notice, since the car was purchased with the brake calipers dismantled and living in a cardboard box in the front trunk.  Attempting to mount the front brake calipers earlier would have revealed the issue, because on the hub pictured above, it would have been impossible.  The first ‘fish of hintiness’ was when both front hubs were removed to be resurfaced, and they appeared to be different parts.  As it turns out, the one hub that was too worn to resurface was the correct part. Not thinking much of it, I discarded it and bought another that looked identical to the wrong hub, pressed in the bearing outer races, cleaned them up, and painted them to prepare for reinstallation.


Here is where the headache begins.  I can assure you that both the bearing races are perfectly well seated, yet in the image above, the hub does not appear to sit as deep on the axle stub as it should.  Notice the sizable offset between the brake disc and the protective backing plate.  If this were a picture of an upside-down man, his hat is just starting to fall off his ears.


“Therein lies the rub,” to misquote Shakespeare.  When the slot in the front brake caliper was fitted over the rotor disc, that offset kept it from clearing the mounting nubs on the axle stub.  The picture above shows them bumping their little red knuckles on those nubs.  Since the worn out hub/rotor had already been replaced with the new incorrect one, both of the existing front hubs were now misbehaving in the same way, leading to speculation that other components were to blame: mismatched brake calipers, axle stubs, or out-sized bearings.  Who knows what mischief the previous owner had wrought?  I went to bed with a question mark haunting my dreams.


In the morning, a well-placed phone call put me in direct contact with George Hussey, the owner of Automobile Atlanta,  and a champion of the Porsche 914 since 1978.  George is on a mission to save the 914, and said he would answer questions all day even if I never bought another auto part from him.  I’m sure my account records show how much I have already spent!   He quickly set me straight about the correct hub/rotor for my year car, and also answered a crapload of other questions about my brakes.  So I cruised over to the shop where I bought the wrong early model rotor and exchanged it for a brand new correct one, still in the box.  No surprise;  it looked exactly like the worn rotor that was discarded.  The first indication of a late model rotor is the centering ring that surrounds the grease cap, as seen above.


Continuing with the upside-down hat metaphor, notice how the brim is now sitting properly over the “ears.”  If viewed side-by-side, the later model rotor will literally have a higher hat.  Also notice that the inside surface of the brake disc is now only a few hairs away from the protective back-plate.


When slipped over the disc, the brake caliper now easily clears the mounting nubs on the axle stub, and the holes align properly for the mounting bolts.  The image above shows the caliper fastened securely to the axle with 10.9 grade hardened, black anodized 14mm bolts.  As it should be.  Everything finally back in order. Mission accomplished.  And there dies the rub.


One Response to “Therein Lies the Hub”

  1. […] brake pads clipped smoothly into their slots without complaint.  However, both front rotors were discovered to be pre-1973, which fit incorrectly and made it impossible to mount the front brakes.  I headed back to […]

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