04.10How to replace the front brakes and wheel bearings on a Porsche 911SC
The design of the Porsche 911SC brakes requires that the brake calipers and wheel hubs be removed in order to replace the brake discs which are mounted to the back of the hubs, the hubs contain the front wheel bearings. At this time I am going to replace the front wheel bearings, grease seals, brake rotors, brake pads, and front brake hoses. This job will require that the brake system be bled out so I also plan to flush the hydraulic system completely with fresh DOT-4 fluid.
This job is relatively simple but since it involves the braking system as well as the wheel bearings and associated hardware that hold the wheels onto the car it is essential that all work be performed carefully and completely.
RECOMMENDED TOOLS
-Floor jack and jack-stands or an automotive lift
-1/2″-drive ratchet or breaker-bar
-19mm 1/2″ drive socket for lug nuts and caliper bolts
-1/2″ drive torque wrench (accurate!)
-3/8″-drive ratchet with metric sockets and various extensions
-11mm open-end wrench or line-wrench
-13, 14 and 17mm open-end wrenches
-Large Slip-joint (Channel-lock) Pliers
-Medium-sized hammer
-Various punches
-Bearing race driver set
-6mm hex (allen) wrench or socket
-Latex or Nitrile gloves
-Lots of rags
-A friend to assist with brake bleeding or a pressure bleeder
-Brake cleaner
Let’s get started!
*Notes:
-Photos are clickable for larger more detailed pictures.
-Leave the keys in the ignition so you will be able to turn the wheels side-to-side.
-Before raising the car loosen the front wheel lug nuts.
-Never rely on a jack alone to support a vehicle!
Here are the new brake components that will be installed.
These are the new bearings and seals.
Use the jack or lift to raise the car high enough to get the front wheels off the ground. If using a jack make sure to place the jackstands securely under the frame.
Up in the air and ready to go.
Once the car is lifted and safely supported remove the front wheels.
You’ll now have access to the Brake and wheel-hub assembly.
Use an 11mm wrench to remove the caliper hydraulic line where it enters the caliper, if replacing the rubber lines undo the fitting above after removing the large retaining clip (pictured below). Plug the end of the line and the caliper to prevent excessive brake fluid spillage.
Remove the two 19mm brake caliper securing bolts.
The caliper is now free and can be pulled off the brake rotor.
With the caliper off drive out the brake pad retaining pins with a small punch.
Caliper disassembled.
Clean the calipers thoroughly with brake cleaner, a soft brush, and rags. Castrol Super Clean and warm water is another option that works very well for removing that stubborn brake dust and grime. Set the calipers aside to dry. Now it’s time to replace the wheel bearings.
Use a pair of large channel lock pliers to grip and remove the bearing dust-cap from the wheel hub. Underneath you will find the bearing lock-nut.
Loosen the 6mm hex pinch-bolt on the bearing lock nut then remove the nut and washer. You can now pull the complete hub and rotor assembly from the car. Once removed wipe as much grease as possible from the inside of the hub and the axle spindle.
Remove the 5 13mm nuts and bolts that secure the brake disc to the aluminum hub and discard the disc (unless you are planning to reuse or resurface the rotors). Clamp the hub in a vise and use a large flat-tip screwdriver or seal-puller to remove the inner wheel bearing seal.
Withdraw the seal and the inner bearing and clean the hub thoroughly with solvent or brake cleaner and plenty of rags. The bearing races are pressed into hub and must be tapped-out using a long punch and a hammer. Take your time and work carefully to prevent gouging or damaging the soft hub material when removing the steel races. Tap on the exposed lip of the bearing race as shown.
Hub shown with the races removed.
I prefer to work with clean parts so I recommend cleaning the hubs again with the races removed. Make sure the bores where the races sit are smooth and undamaged, if you nicked the edges while tapping-out the old races use a bit of emory cloth or a small file to smooth any imperfections before installing the new bearing races.
The Bentley service manual recommends that the hubs be heated to 250 degrees F. to aid in the installation of the new bearing races, while not essential it does expand the metal and ease installation greatly, (also adds a pleasant smell to the oven)!
The new races can be installed with a punch but care must be taken avoid any damage to the surface where the bearings will ride. A bearing install kit is an inexpensive way to install the races without damage. Select the proper sized attachment and tap the new races into place as shown below.
Carefully tap in the new race.
The hub showing the races fully seated.
Gloves are a must for the next few steps. Use a high-quality wheel bearing grease to lubricate the new races and pack the wheel bearings, also add plenty of grease to the insides of the hub. I’m old fashioned and prefer packing the bearings by hand rather than using one of the many available bearing-greasing devices, the clean-up is easier too, just peel off the gloves and toss them when the job is done.
Packing the new bearings with grease. (To do this by hand place a large glob of grease in your palm and force the bearing into it until grease comes out the inside of the rollers as shown. Make sure it is well lubricated).
Wheel hub with the bearings fully greased and installed.
Now place the new grease seal in position and tap gently into place. Make sure to install it squarely and tap evenly around the outside edge to prevent distorting the seal. If the metal is bent or distorted the seal will not work properly.
Wheel bearing seal installed.
Clean the new brake rotors of any contaminants or rust-preventative oils then
attach to the wheel hubs using the 5 bolts and torque the 13mm nuts to 18 ft. lbs. Carefully slide the hub onto the spindle and install the grease-packed outer bearing, washer, and retaining nut.
Tighten the retaining nut firmly while spinning the hub assembly, then back the nut off and re-tighten it until the washer can just barely be moved with a screwdriver. It is important that the bearings have some pre-load without being too tight. If you can’t wiggle the washer at all they are too tight, if the washer moves freely or you can feel play in the disc they are too loose. When the bearing pre-load is correct tighten the lock-nut pinch-bolt to 11 ft./lbs. then tap the dust cap back into place.
Use large channel lock pliers to slowly compress the brake caliper pistons back into the caliper. Note: If the caliper pistons will not retract, the dust boots are torn or missing, or there is visible fluid leakage from around any of the pistons it is time for the calipers to be rebuilt or replaced, do not reinstall damaged or nonfunctional brake components!
Once the pistons are fully retracted into the caliper bores you can install the caliper. I like to add a few drops of blue loctite thread locker to the caliper mounting bolts for extra peace of mind.
Install the caliper bolts and torque to 94 ft./lbs. Then reinstall the brake fluid line to the caliper.
There are a million or so products on the market designed to prevent disc brakes from squeaking or squealing. I recommend using one of them to coat the back of the brake pad where it contacts the piston. Brake noise is usually caused by the pads vibrating and resonating in the calipers when the brakes are applied, a light coating of lubricant between the pad and piston is often all that is needed to prevent this.
Slide the pads into the caliper.
Reinstall the pad retaining pins and spring-plate.
Use a punch to drive the pins fully into the caliper and the brake job is nearly done.
All that is left is to bleed out any air and then reinstall and torque the wheels. Top-up the brake fluid reservoir with fresh fluid and open one of the caliper bleed screws using a small hose to catch fluid in a suitable container. Have your friend, assistant, wife, or complete stranger pump the brake pedal until clear bubbe-free fluid is coming out of the caliper, then move to the other side making sure that the fluid reservoir does not run out of fluid. Reinstall the road-wheels and torque to specs.
*Notes on safety with new brakes.
-Pump the brakes several times before starting the car to move the pads against the rotors and verify the pedal feels good and there are no fluid leaks.
-It is important to drive the car gently as the pads will need to fully seat and wear-in to the new rotors before maximum braking effect is possible. There are many opinions on the proper method for breaking-in new brakes and I will not get involved in that discussion here but to simply recommend taking it very easy on the brakes for at least the first 100 miles or so.
-It is good practice to remove the wheels and inspect the brake and bearing components after the first test-drive to verify that everything is tight and leak-free.
-Most importantly if you have any doubt or problems with the brake system do not continue to drive the car! find and repair the fault or have it towed to qualified shop for repairs.
Porche wheel bearings are not cheap.
Thanks for the great article though!
May 9th, 2009 at 6:50 am
Thank you for the comment. The 911SC front bearings are shared with a variety of VW and Audi vehicles and are available from aftermarket suppliers at less than $10 each. If you order by the VW number and not the Porsche number you can save a lot. Part number for the inner bearing (same a VW Bus) is 211-405-625 and the outer is 443-505-509. (These may cross to a Timken or FAG part number as well?)A complete set of bearings and seals is available for less than $50 from Pelican Parts
May 9th, 2009 at 8:54 pm
Thank you for the article. I’m new to wheel bearing / brakes replacement but after 10+ years owning my car and tool set, I figure it’s now time to do so. Can you refer me to a procedure for changing wheel bearings on a 1995 911 (993)? After removing the rotor, I see a 32 mm bolt head on the inboard side that appears to be connected to a 32 mm nut on the outboard side. I haven’t managed to loosen the nut. Is there a trick, or do I just have to put more force on it to loosen it?
July 26th, 2009 at 11:46 am
Congratulations on a great car Chester, the 993 is one of my favorites! On your car the front wheel bearing is single sealed unit, the bolt and nut you describe should be very tight, (I will update with the torque spec.), they hold the wheel hub in the bearing while keeping the bearings halves pressed together. The bearings can be replaced in the car using a set of special tools but Typically the steering knuckle is removed as a unit then the hub is pressed-out using a hydraulic press, under the hub there is a metal plate that retains the bearing, once that is removed the bearing itself can be pressed from the steering knuckle. It is a bit more involved than the process I describe on the older 911. I’ll update this if I can find a good guide or better yet I will try to create one next time I have a chance to work on a 993.
July 26th, 2009 at 9:29 pm
Paul,
On a 88 Carrera, is there a clip at the strut that could be removed and allow the caliper to be moved aside instead of disconnecting the brake hose and having to re-connect and bleed the caliper after?
I am looking to work on the bearings only and hope not to have to deal with bleeding the brakes.
Thank you
Raul
August 22nd, 2009 at 2:40 pm
If I recall correctly the Carrera front brake hoses and calipers are mounted the same as the SC. There is a clip that secures the flexible brake hose but I believe it is used at the body side of the hose, with a spring clip (like the SC connection shown here I may be wrong though, if so let me know what you find. -Paul
Edit: Looking at the parts diagrams at Pelican Parts it appears there was a model year change to the brake mounting in ’88, so your car may have the clips mounted out at the struts making it possible to maneuver the calipers out of the way without disconnecting them.
Re-Edit! I checked out an ’88 Carrera today and the lines are indeed the same as an SC, the hardline to the caliper is connected to the flex line at the strut and must be removed in order to get the caliper off to remove the hub/disc.
These are photos of the car:
Clip holding flexline to the body
Connection at strut that must be disconnected
Connection at the strut
August 23rd, 2009 at 5:15 am
I am currently doing the same job. I am at the point of cleaning the hubs. How did you clean yours? I am having problems getting down into the all the areas of the hub. Once they were clean did you do anything to protect them?
October 27th, 2009 at 8:33 pm
I’ll be honest Don, I cheated. I had mine in a hot-water pressure cleaner for quite some time and they were still dirty. Next I used a scrub-brush and some purple cleaner which got off most of the remaining grime. They look good in the photos only because I hit them with a coat of dull aluminum spray paint which actually holds up well and makes them look brand new.
Good luck with your project and thanks for reading!
-Paul
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