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From digest.v7.n1800 Sat May 30 19:47:47 1998
Date: Sat, 30 May 1998 18:16:17 EDT
Subject: Re: Brake rotor hold-down bolt.

>>My buddy was losing patience and
suggested that we drill right through sonce screw is intended only to hold in place rotor while mounting calipers.

We successfully drilled screw (between lug holes), and removed rotor. My concern is, how serious is that screw? I have 1 rotor without screw... I'm assuming 5 lug bolts are more than enough for tightening of rotor in proper position.<<

Been there, done that, sort of...

The rotor hold-down bolt does keep the rotor from half falling off whenever you remove the wheel, changing brake pads, etc. It also holds the lug holes through the rotor hat in alignment with the threaded lug holes in the hub. However, if the wheel lugs become loose, you will have a disaster waiting to happen, as the rotor hat will move against the lug bolts under serious braking (and acceleration for rear wheels), placing them in a shear mode they were not designed to handle.

However, the correct procedure to remedy the situation is to use a drill bit 1/4" smaller in diameter than the rotor hold-down bolt head diameter. You drill down only far enough to drill the head of the bolt loose from the threaded shaft; the head of the bolt is much larger in diameter than the threaded shaft. If you remove the bolt head as described above, once you pull the rotor the head-less shaft of the bolt will be protruding out far enough to grap it with a pair of vice grips. It is the head of the bolt that is usually seized against it's alignment position in the rotor hat, not the threads; the head-less bolt shaft should remove easily.

ALWAYS be sure to smear a thin coat of anti-seize on the new rotor hold-down bolt and its rotor mounting hole, also smear a very thin coating of anti-seize on the rotor-to-hub mounting area to make the rotor easy to remove at a later date. If you remove/replace the caliper mounting bracket bolts, be especially sure to anti-seize these bolts, too. DO NOT use anti-seize on the caliper slide pins; use only heat-resistant caliper pin grease. Same for the caliper/pad slide points.

If you made the mistake of drilling all the way through the hub I'd recommend replacing the hub, or at least trying to re-thread the hole in the damaged hub, and replacing the rotor hold-down bolt.

Mark Sipe

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