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Pelican Technical Article:
Front Brake Rotor or Disk Replacement

 
Time: 3 hours
Tab: $100-$300
Talent:  
Tools:
13mm, 19mm socket, 11mm flared wrench, large channel locks, 6mm Allen wrench
Applicable Models:
Parts Required:
New rotors or disks
Hot Tip:
Clean any contaminants off the new rotor or disk before installing the caliper
Performance Gain:
Car stops better
Complementary Modification:
Replace pads
 
   

   

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     Replacing the front brake rotor/disks on a 911 involves removing the wheel hub from the spindle as the rotor/disk is attached to the hub. While this is not difficult to do it does involve a few more steps. Also “while you are in there” you can check the condition of your wheel bearings. Please see our article on replacing your front wheel bearings for more information. In general, you should inspect your brake pads and rotor/disks about every 25,000 miles, and replace the pads if the material lining of the pad is worn down to less than a quarter inch. If you ignore the wear on the pads you may indeed get to the point of metal on metal contact, where the metal backing of the pads are contacting the brake discs.  Using the brakes during this condition will not only give you inadequate braking, but will also begin to wear grooves in your brake discs.  Once the discs are grooved, they are damaged, and there is often no way to repair them.  Resurfacing will sometimes work, but often the groove cut will be deeper than is allowed by OEM specifications.  If your pads are grabbing or pulsing when you come to a stop, there is a very good chance your rotor/disks are warped and in need of replacement as well. NOTE: If your rotor/disks are really grooved you should replace your brake pads as well. In reality, most people don’t inspect their discs or pads very often, and with the early 911’s there is no little brake-warning lamp to appear on the dashboard.  It's a wise idea to inspect your pads every oil change.

     The first step is to jack up the car and remove the road wheels. Please see our article on safely jacking up and supporting your 911.

     To replace the front rotor/disks on the 911 you need to remove the caliper. The 911 brake calipers brake lines are attached in a manner that you will need to break or separate the line from the caliper. There is no way to “hang” the caliper attached to the line while performing this job.

     Since you are going to be opening up the brake system you will need to bleed your brakes before you drive the car again.

     Begin by using something to depress and hold the brake pedal down about an inch. This will help stem the flow of brake fluid. I like to wedge a piece of wood between the seat and pedal.

     With the wheel off you can see the rotor/disk, caliper and brake pads.

     On the rear of the caliper there are the two 19mm mounting bolts as well as the incoming brake line. Use an 11mm flared nut wrench and remove the brake line from the caliper. Brake fluid is deadly to paint so make sure you do not get any on painted surfaces or on your hands and then touch painted surfaces. You should cap the hard line to stop the flow of fluid and to help prevent any contaminants from getting into the line.

     Move to the front of the caliper and use a punch or small screwdriver to tap out the two retaining pins. Take care as you do this as the retaining spring is under some pressure. With the pins removed remove the retaining spring.

     Use a large screwdriver between the pad and disk or a large set of channel locks and a rag to protect the caliper and compress the caliper piston back into the caliper. Brake fluid will flow back out of the caliper at this time so be prepared. This will make removing the caliper from the disk easier, especially if the disks are worn.

     Next remove the two 19mm bolts holding the caliper to its mount.

     After the guide bolts have been removed, you should be able to simply lift the caliper off of its mount.

     Once you have the caliper removed, inspect the inside of it.   Make sure that the dust boots and the clamping rings inside the caliper are not ripped or damaged.  If they are, then the caliper may need to be rebuilt. 

     Once the calipers and pads are removed, you'll have access to the wheel bearing hub. Remove the dust cap from the front of the wheel hub. You will need a very large set of vice grips or channel locks to grasp and gently rock the dust cap off.

     With the dust cap removed you can see the axle nut that sits at the center. It's a good idea to wipe off any excess grease on the nut off. Use a 6mm Allen key to loosen the bolt on the axle nut. This bolt holds the axle nut in place on the spindle. Once you loosen the bolt, you should be able to easily unthread the nut from the spindle.

     With the axle nut removed, you will be able to pull the hub off. As you do, the outer wheel bearing will pop out. The tapered bearing sits inside a race that is pressed into the hub. Check the races and bearings for any signs of discoloration or pitting. These are signs that the bearing is worn and requires replacement.

     Move the rotor/disk hub combination to your bench and separate them using two 13mm sockets.

     Carefully clean the surface area on the hub where the rotor/disk mounts.

     Install the new rotor/disk to the hub and torque to spec.

     Now fit the wheel hub back over the spindle and push it back until the seal pops over the flange on the back of the spindle. Install the outer bearing keeping in mind that the tapered section of the bearing fits into the race facing inward.

     You'll now need to adjust the wheel bearing. While rotating the disc and bearing hub tighten the locking nut in small increments until the thrust washer can barely be moved back and forth with the light push of the tip of a screwdriver. Then tighten the 6mm bolt on the end of the nut to spec.

     Put a little of the high temp grease on the inside of the dust cap and place it back onto the hub. Use a hammer to lightly tap the hub back into place.

     Reinstall the calipers, brake pads and brake line. Make sure you clean the rotor/disk of any dirt, oil or grease.

     Note: you must bleed the brake system before you attempt to drive the vehicle. Please see our article on how to bleed your brakes.
Begin by using something to depress and hold the brake pedal down about an inch.
Figure 1
Begin by using something to depress and hold the brake pedal down about an inch. This will help stem the flow of brake fluid. I like to wedge a piece of wood (yellow arrow) between the seat and pedal.
Large Image | Extra-Large Image
With the wheel off you can see the rotor/disk (red arrow), caliper (blue arrow) and brake pads (yellow arrow).
Figure 2
With the wheel off you can see the rotor/disk (red arrow), caliper (blue arrow) and brake pads (yellow arrow).
Large Image | Extra-Large Image
On the rear of the caliper there are the two 19mm mounting bolts  (red arrows) as well as the incoming brake line (yellow arrow).
Figure 3
On the rear of the caliper there are the two 19mm mounting bolts (red arrows) as well as the incoming brake line (yellow arrow). Use an 11mm flared nut wrench and remove the brake line from the caliper. Brake fluid is deadly to paint so make sure you do not get any on painted surfaces or on your hands and then touch painted surfaces.
Large Image | Extra-Large Image
You should cap the hard line (yellow arrow) to stop the flow of fluid and to help prevent any contaminants from getting into the line.
Figure 4
You should cap the hard line (yellow arrow) to stop the flow of fluid and to help prevent any contaminants from getting into the line.
Large Image | Extra-Large Image
Move to the front of the caliper and use a punch or small screwdriver to tap out the two retaining pins (yellow arrows).
Figure 5
Move to the front of the caliper and use a punch or small screwdriver to tap out the two retaining pins (yellow arrows). Take care as you do this as the retaining spring (red arrow) is under some pressure. With the pins removed remove the retaining spring.
Large Image | Extra-Large Image
Use a large screwdriver (red arrow) between the pad and disk or a large set of channel locks and a rag to protect the caliper and compress the caliper piston back into the caliper.
Figure 6
Use a large screwdriver (red arrow) between the pad and disk or a large set of channel locks and a rag to protect the caliper and compress the caliper piston back into the caliper. Brake fluid will flow back out of the caliper at this time so be prepared. This will make removing the caliper from the disk easier, especially if the disks are worn.
Large Image | Extra-Large Image
I prefer to use a set of large channel locks and a rag (yellow arrow) to push the pads back in.
Figure 7
I prefer to use a set of large channel locks and a rag (yellow arrow) to push the pads back in.
Large Image | Extra-Large Image
Next remove the two 19mm bolts holding the caliper to its mount (red arrows).
Figure 8
Next remove the two 19mm bolts holding the caliper to its mount (red arrows). After the guide bolts have been removed, you should be able to simply lift the caliper off of its mount.
Large Image | Extra-Large Image
Once the calipers and pads are removed, you'll have access to the wheel bearing hub.
Figure 9
Once the calipers and pads are removed, you'll have access to the wheel bearing hub. Remove the dust cap from the front of the wheel hub (yellow arrow). You will need a very large set of vice grips or channel locks to grasp and gently rock the dust cap off.
Large Image | Extra-Large Image
With the dust cap removed you can see the axle nut that sits at the center.
Figure 10
With the dust cap removed you can see the axle nut that sits at the center. It's a good idea to wipe off any excess grease on the nut off. Use a 6mm Allen key to loosen the bolt (yellow arrow) on the axle nut. This bolt holds the axle nut in place on the spindle. Once you loosen the bolt, you should be able to easily unthread the nut (red arrow) from the spindle.
Large Image | Extra-Large Image
With the axle nut removed, you will be able to pull the hub off.
Figure 11
With the axle nut removed, you will be able to pull the hub off. As you do, the outer wheel bearing will pop out (yellow arrow). The tapered bearing sits inside a race that is pressed into the hub. Check the races and bearings for any signs of discoloration or pitting. These are signs that the bearing is worn and requires replacement.
Large Image | Extra-Large Image
Move the rotor/disk hub combination to your bench and separate them using two 13mm sockets (yellow arrows).
Figure 12
Move the rotor/disk hub combination to your bench and separate them using two 13mm sockets (yellow arrows).
Large Image | Extra-Large Image
Carefully clean the surface area on the hub where the rotor/disk mounts (yellow arrow).
Figure 13
Carefully clean the surface area on the hub where the rotor/disk mounts (yellow arrow).
Large Image | Extra-Large Image
Install the new rotor/disk to the hub and torque to spec.
Figure 14
Install the new rotor/disk to the hub and torque to spec.
Large Image | Extra-Large Image

Figure
Large Image | Extra-Large Image
You'll now need to adjust the wheel bearing.
Figure 16
You'll now need to adjust the wheel bearing. While rotating the disc and bearing hub tighten the locking nut in small increments until the thrust washer (yellow arrow) can barely be moved back and forth with the light push of the tip of a screwdriver. Then tighten the 6mm bolt on the end of the nut to spec.
Large Image | Extra-Large Image
Put a little of the high temp grease on the inside of the dust cap (yellow arrow) and place it back onto the hub.
Figure 17
Put a little of the high temp grease on the inside of the dust cap (yellow arrow) and place it back onto the hub. Use a hammer to lightly tap the hub back into place.
Large Image | Extra-Large Image
Reinstall the calipers, brake pads and brake line.
Figure 18
Reinstall the calipers, brake pads and brake line. Make sure you clean the rotor/disk of any dirt, oil or grease. Note: you must bleed the brake system before you attempt to drive the vehicle. Please see our article on how to bleed your brakes.
Large Image | Extra-Large Image
Need to buy parts for this project?
Click here to order parts for your BMW from our parts catalog
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