[A8] Bolt size holding on front (Lucas) calipers?

Rich, Jack JRich at Kronos.com
Sun May 7 22:34:38 EDT 2006

The correct answer is 21mm.

That was the most difficult PITA brake job I've ever done.  Although the pads are about the easiest to change I've ever seen (you don't have to remove or loosen the calipers) replacing the rotor wins the prize for most difficult brake system I've seen.  First, those 21mm bolts are on inordinately tight and 2nd, one of them is inaccessible behind the ABS wiring harness mount.  It was also the first time I've ever changed brakes that the disc was frozen on.  Not just a little, but 20-minutes-pounding-with-a-hammer stuck on.  They didn't need replacing very badly, but I'd bought rotors, and once I started hitting it, I no longer wanted to leave it on.  Normally I buy rotors because if you are going to replace the pads, you might as well do rotors while you are in there.  I recommend against that on this car and replace them only when necessary since the pads are really easy and the calipers are a bitch.  I left the original rotor on the other side, as it also was at least a little stuck and otherwise seemed in fine shape and hadn't been hit.  I now have one spare rotor for next time, when my passenger side will need it and my driver's side won't.

Oh, one last thing to go wrong: the pads from Tire Rack had the wrong wear-wiring connector, so I had to solder the original connector from the old pads to the new pad wires.


-----Original Message-----
From: a8-bounces at audifans.com [mailto:a8-bounces at audifans.com]On Behalf
Of Rich, Jack
Sent: Saturday, May 06, 2006 5:06 PM
To: A8 Audifans (E-mail)
Subject: [A8] Bolt size holding on front (Lucas) calipers?

I went to replace my front rotors and found that the bolt holding on the caliper was larger than my largest size of 19mm. I've never encountered this problem doing brakes before. Does anyone know what size bolt this is? This is a 2001 A8L with the Lucas calipers (with the dual piston, 4 pads per caliper.) 


Jack Rich
Senior Member of Technical Staff
Improving the Performance of People and Business(tm)

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