Checking the thickness of the brake linings
As a rule, a change in the thickness of the brake linings by 1 mm corresponds to a vehicle mileage of at least 1,000 km. However, this rule is valid only under unfavorable operating conditions. Under normal conditions, pads last much longer. Shine a flashlight through the hole in the wheel disc on the caliper. You can even remove the rear wheel to get a better view of the brake pads. With a brake pad thickness of 7 mm, the wear limit has been reached and the pads must be replaced. This measurement also measures the rear lining plate. This measurement is made in the same way as described earlier for the front wheel brake.
Replacement of brake pads
If the brake pads are reinstalled, they must be marked in accordance with their previous position. Although the clips look the same as on early Audi models, the pistons have been changed and now require a special tool to make the self-extinguishing pistons (through the adjustment mechanism) screw back into the hole before inserting new brake pads. The pistons have two grooves located opposite each other, on which the trunnion key is installed. If it is not available, then a steel strip with the width of the piston and the width of the groove for screwing can be used.
Raise the rear of the car on stands and remove the wheel.
Unscrew the bottom hex bolt of the cylinder body with a ring wrench, while holding the guide pin on the hex with an open-end wrench, as shown in the figure. If you do not hold the hex, then the guide pin will rotate and destroy the mount. Naturally, the open-end wrench must be thin enough to be inserted into the slot. Unscrew the fastening bolt at the top in the same way.
Raise the cylinder body and fasten it together with the hose in a suitable way to the rear suspension parts.
Brake pads are now free and, having previously marked, they can be removed (if they are reused).
Clean the guide surfaces or the seat in the housing bore with compressed air, if available, and if not, with a rag. Never inhale blown dust from brake pads. Do not use mineral-based solvents or sharp-edged tools. Check the protective cap at the end of the piston, hardened caps must be replaced. Before installing the brake pads, check the brake disc. If there are deep scratches, remove the brake disc and regrind or replace it. In chapter "Brake disc processing" there are instructions for this.
When installing the brake pads, proceed as follows:
Screw the piston with the special pin wrench mentioned above into the caliper cylinder. In doing so, apply pressure to the inside.
See the next section for instructions on how to unscrew the piston without a tool. Before pushing in, remove some brake fluid from the reservoir, as otherwise, liquid may leak out of the reservoir and damage the paintwork. Brake fluid is poisonous! In no case should you suck out the liquid with your mouth through a hose, but use a blower or something similar. Collect liquid in a bottle.
Insert brake pads. You may need to move the piston further. Make sure that the shoes are properly seated in the positions indicated by the arrows before reinstalling the cylinder body.
Install the cylinder body on the brake disc and secure with new self-locking bolts. The tightening torque is 30 Nm. Each brake pad repair kit contains new bolts for each brake caliper.
Attention: The bolts used to fasten the rear caliper carrier are tightened with a torque of 95 Nm (ribbed bolts) or 6Nm (hex socket bolts).
Now you can install the brakes in the main (initial) position, i.e. check parking brake adjustment.
Lower the vehicle to the ground and tighten the wheel nuts.
Add brake fluid to reservoir.
Press the brake pedal several times. so that the brake pads fit properly on the disc. New pads must run in, i.e. at the beginning of their operation, you need to brake carefully.
Repair of brake calipers
Elements of the rear brake caliper
1 Self-locking bolts 3Nm
2 Brake caliper housing
3 O-ring (cuff) cylinder
4 Piston with regulator, diameter 38 mm
5 Dust cap
6 Brake caliper carrier
7 Screw (valve) to remove air
8 Dust cap
9 Guide pin (finger)
10 Rubber cuff
Clamp the cylinder in a vice with soft jaws and first clean thoroughly with brake fluid or alcohol. Loosen the parking brake cable fixing bolts.
Using a special wrench, unscrew the piston from the caliper. Install the key protrusions into the piston recess shown by the arrow.
On the other side there is a similar notch. If you use a piece of steel strip of the same width as the piston and suitable thickness for the recess, then with it you can also unscrew the piston. Do not damage the edges of the recess.
Carefully pry out the O-ring with a screwdriver (cuff) from the inside of the cylinder bore.
Thoroughly clean all parts if the cylinder is in good condition and use parts from the repair kit when reassembling. If the caliper carrier is being replaced, then install it, lubricated, on the guide pins. Replace the carrier or replace the protective collars using a repair kit if the protective collars or guide pins are damaged.
Lubricate new O-ring (cuff) brake fluid or special grease and insert it into the groove.
Using a screwdriver, carefully press the inner sealing lips of the dust ring into the cylinder groove.
Install the special wrench mentioned above or a steel strip in the piston and unscrew the piston inward. While screwing in, apply a uniform force to the piston. When the piston sits in place, the outer sealing lips of the dust ring will fit into the groove of the piston.
Lubricate the bleeder valve with special brake grease and screw it on. The brake caliper must first be bled of air. To do this, put the bleed hose on the bleed valve, and put the other end of the hose on a syringe filled with brake fluid. You can use a rubber bulb, which should be well cleaned before that. Inject brake fluid until it comes out of the brake hose hole free of air bubbles.
The caliper is now ready for installation.
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