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Rear Brake Disc Replacement (Note: There is no Rear Brake Pad Replacement article.)
 

Pelican Technical Article:

Rear Brake Disc Replacement (Note: There is no Rear Brake Pad Replacement article.)

Jared Fenton

Time:

2 hours2 hrs

Tab:

$40 to $80

Talent:

***

Tools:

10mm hex driver, dead-blow hammer, wire brush, penetrant spray

Applicable Models:

A6 2.7T (1997-04)
A6 2.8 (1997-02)
A6 3.0L (2002-04)
S6 4.2 (1997-04)

Parts Required:

Rear Brake Discs

Hot Tip:

Put a light coat of anti-seize compound on the hub face

Performance Gain:

Better braking

Complementary Modification:

Replace Brake Pads

Brake discs (or rotors as they are often called) are perhaps the most important part of the braking system. The brake pads rub against the disc to slow the car down. At the same time, the disc also dissipates heat from the friction generated. If the disc becomes too thin or develops grooves in the surface, then its ability to stop the car decreases.

When replacing your brake pads, measure the thickness of your brake discs. If they fall below the specified value, replace them with new ones. Check for grooves in the disc, and make sure that you take several measurements of the rotor in several different places. This will guarantee you that you get an accurate reading. If the brake disc has a groove in it, then it should most certainly be resurfaced by a machine shop, or simply replaced with a new one. Discs with grooves not only brake less efficiently, but they also heat up to higher temperatures and reduce your overall braking ability. Additionally, the discs can warp from the excess heat generated.

Use a micrometer to measure the thickness of the brake disc. From the factory, the rear brake disc on your A6 will be 14 mm thick. The wear limit is 11 mm. If the thickness is adequate, you can have the rotors turned on a lathe to remove glazing and grooves from the old discs. In practice, I usually just replace the discs. It's a bit more money, but you get peace of mind.

Replacing brake discs is a pretty simple job. For front brake disc replacement procedure see our article Front Brake Disc Replacement.

The first step is to jack up the car and remove the road wheels. If you haven't already, remove the caliper and brake pads. Refer to our article on Rear Brake Pad Replacement for more details.

Now unbolt the caliper frame from the wheel hub. You'll need a 10 mm Allen to remove these bolts. After you remove the bolts, you should be able to move the caliper frame up and off the wheel hub. At this point, you should be able to slide the disc off the hub.

If there is any resistance, the disc may require some heavy smacks with a dead-blow hammer to get it off. This was the case on our project car, being from the Pacific Northwest. The increased moisture causes the metals to corrode and lock the rotor to the hub. In extreme cases, you may need to spray the holes in the disc with a good penetrant spray, such as Aerokroil, and let it sit for a few hours. This can sometimes free up the rotor. If all else fails, heating the disc area around the hub with a shop torch can free up the rust.

It's a good idea to clean the face of the wheel hub once the disc is removed with some brake cleaner and a soft brush. Once clean, I like to put a light coat of anti-seize compound on there. It helps to prevent corrosion and also keeps the disc from sticking to the hub.

After the new disc is installed, reinstall the caliper frame and the mounting bolts. Your new discs should last a long time, and you should see an improvement in your braking after the wear-in period for your new brake pads.

Removing the disc requires removing the caliper mounting frame (green arrows) from the rear of the wheel hub.
Figure 1

Removing the disc requires removing the caliper mounting frame (green arrows) from the rear of the wheel hub.

Loosen and remove the two 10 mm Allen bolts (green arrows) holding the frame to the wheel hub.
Figure 2

Loosen and remove the two 10 mm Allen bolts (green arrows) holding the frame to the wheel hub. You may need to use a breaker bar to get them loose. The disc should now just slide off the hub. If it is stuck, try using some penetrant spray around the stud holes and let it sit for a few hours. You may also need to use a dead-blow hammer behind the disc to loosen it up.

Installing the new brake disc is the reverse order of removal.
Figure 3

Installing the new brake disc is the reverse order of removal. I suggest applying a thin layer of anti-seize compound on the mounting surface of the disc where it meets the hub.


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Page last updated: Thu 12/14/2017 03:23:07 AM