bmwrepairs: How to replace Brake Caliper on bmw 325?

Brake Caliper

Overhaul

NOTE

If the vehicle is equipped with ASC+T, the BMW Service Tester must be used to properly bleed the system. Due to safety and liability issues, this job should only be performed by a BMW dealer.

The overhaul procedure covers replacement of the seal, dust boot and guide sleeves. If the piston or bore is found to be pitted or corroded, replacement of the caliper is recommended. Use a original manufacturer overhaul kit. Use all the parts contained in the kit. Work in a clean, dust free area. Use only an approved brake cleaner or isopropyl alcohol and non-lubricated compressed air to clean the caliper and parts.

To overhaul the brake caliper, the brake caliper piston must be removed.

There are two different ways to remove the piston from the caliper. It can be pumped out using the foot brake or removed using compressed air.

When removing a brake caliper piston using the foot brake:

Only one caliper can be overhauled at a time

The piston is pumped out before the brake line is loosened or disconnected

This procedure takes more time than the compressed air method, however if the caliper piston is severely seized, compressed air may not be able to move the piston. Therefore pressing the piston out hydraulically may be the only option short of replacing the caliper assembly.

This method requires the brakes to be bled every time a hydraulic line is opened.

If the brake caliper piston moves relatively freely, removing the piston with compressed air works well and is much less time consuming than other methods.

CAUTION

NEVER place your fingers in front of the pistons in an attempt to catch or protect the pistons when applying compressed air. This could result in personal injury!

To remove the piston via compressed air:
1. Remove the caliper from the vehicle and place on a clean workbench.
2. Stuff a shop towel or a block of wood into the caliper to catch the piston.
3. Remove the caliper piston using compressed air applied into the caliper inlet hole. Inspect the piston for scoring, nicks, corrosion and/or worn or damaged chrome plating. The piston must be replaced if any of these conditions are found.

To remove by being pumped out using the foot brake:
1. Work with one caliper at a time:
2. Do not disconnect or loosen the brake hose, otherwise the brake will have to be bled.
3. Place a suitable drain pan under the brake caliper.
4. Remove one brake caliper an place over the drain pan.
5. Press the brake pedal down fully and release the brake pedal slowly, then check the fluid level in the master cylinder reservoir. If the reservoir runs dry, the brake system will have to be bled.
6. Repeat the above step until the caliper piston is dislodged. Some brake fluid will leak out once the piston is dislodged.
7. Disconnect the caliper fluid line.
8. Inspect and overhaul the caliper if possible, otherwise replace it.
9. Reinstall the overhauled or replacement brake caliper completely and bleed the brakes as outlined in this section.
10. Repeat the above steps for each caliper that is to be disassembled.

Fig. Use compressed air to drive the piston out of the caliper, but make sure to keep your fingers clear

Fig. Withdraw the piston from the caliper bore

Fig. Use extreme caution when removing the piston seal; DO NOT scratch the caliper bore

To overhaul:

Remove the piston seals from the groove in the caliper bore.

Carefully loosen the brake bleeder valve cap and valve from the caliper housing.

Clean all parts with an approved brake cleaner or isopropyl alcohol and dry with compressed air.

Inspect the caliper bores, pistons and mounting threads for scoring or excessive wear.

Use crocus cloth to polish out light corrosion from the piston and bore.

If the caliper piston is damaged, severely scored, or out of round, if available, replace the piston, otherwise replace the caliper assembly.

Make sure all components are thoroughly cleaned. The brake caliper piston and bore must be free of all debris. If the upper or lower seal groves in the caliper bore have any built up rust or debris, obtain a small wire brush from a hobby supply store that will fit into a small die grinder or similar tool, and thoroughly clean the grooves. Flush the caliper body thoroughly with an approved brake cleaner or isopropyl alcohol.

Lubricate and install the bleeder valve and cap.

Pour a small amount of fresh brake fluid into a clean container and saturate the new seals with brake fluid. Then, install the seals into the caliper bore grooves, making sure they are fully seated and not twisted.

Lubricate the following with an approved high temperature brake-cylinder paste:

The brake caliper piston bore
The outer circumference of the brake caliper piston
The dust cover/sealing cover

Install the dust cover/sealing cover around the bottom of the piston.

Seat the dust cover/sealing cover lip into the upper groove of the caliper bore.

Once the dust cover/sealing cover is fully seated in the caliper bore, press the piston into the caliper bore slowly and evenly. Do not tilt, or force the piston into the bore. While pressing the piston into the bore, if necessary, slide the upper portion of the dust cover/ sealing cover upward to prevent it from bunching up. Make sure to seat the upper lip of the cover around the brake piston before the piston is completely installed in the caliper bore.

Inspect and if necessary, install new guide bushing sleeves at the slides.

Install the caliper on the vehicle and properly bleed the brake system as outlined in this section.

Install the wheels and hand tighten the lug bolts. Lower the vehicle carefully until the tires begin to contact the surface and torque the lug bolts to specification in a crisscross pattern to 66-81 ft. lbs. (90-110 Nm).

WARNING

Failure to properly torque the wheels to the correct torque using the proper sequence could cause a brake pulsation and rotor warpage.

Press the brake pedal down slowly about 2 inches (50mm), then slowly release. Continue to press and release the brake pedal in slow even 2 inch (50mm) strokes until the pedal is firm.

Removal & Installation

NOTE

If the vehicle is equipped with ASC+T, the BMW Service Tester must be used to properly bleed the system. Due to safety and liability issues, this job should only be performed by a BMW dealer.

Block the rear wheels and apply the parking brake.

Loosen the front wheel bolts ¹ / ₈ of a turn.

Raise and support the vehicle. Remove the front wheels.

If equipped, disconnect the brake pad wear sensor from the harness.

NOTE

Do not loosen or disconnect the brake caliper fluid hose if the caliper is being removed to access or replace another component. Loosen and disconnect the fluid hose only if the caliper is to be replaced, completely removed or overhauled. If the fluid hose is to remain attached to the caliper, support the caliper assembly with mechanic's wire to avoid damaging the line.

If the caliper is to be completely removed from the vehicle (replaced disassembled or overhauled):
1. Siphon the brake fluid out of the reservoir and fix the brake pedal in the depressed position. Or, remove the reservoir cap and place a thin sandwich bag over the opening, then reinstall the cap without the fluid level float to captivate the system. This will prevent brake fluid from draining out of the brake lines while the line is disconnected from the caliper.
2. Using a flare nut wrench, loosen, but do not disconnect the flexible line to the caliper.

Using a suitable prytool, carefully move the tensioning spring toward the brake caliper to release the two retaining tabs and remove the spring.

On E30 models, hold the flats of the pin slides and remove the upper and lower pivot bolts.

On E36 models, remove the two plastic plugs from the caliper slide bolts and using a 7mm hex tool, remove the slider bolts.

Rock the caliper assembly side-to-side several times and then carefully remove the caliper along with the inner brake pad from the brake rotor.

If the brake fluid line is to be removed from the caliper, place a suitable drain pan under the caliper, disconnect and plug the fluid line and the caliper. Note, to avoid damage to the flexible brake line, hold the brake line with a flare nut wrench and spin the brake caliper. If the brake line is sealed to the caliper with a crush washer, replace the crush washer with the appropriate replacement part.

If the brake caliper mounting bracket is to be removed, remove the caliper bracket-to-knuckle mounting bolts and lift off the bracket. These mounting bolts typically require a sturdy 6 point 16mm socket.

NOTE

The brake caliper bracket-to-steering knuckle bolts may require a significant amount of effort to loosen. Use a proper fitting 6 point ¹ / ₂ inch drive metric impact socket and sturdy breaker bar to loosen the mounting bolts.

Fig. The brake caliper mounting bracket is attached to the steering knuckle. The brake caliper is attached to the mounting bracket

To install:

If the brake fluid line was disconnected, connect the brake line to the caliper and torque to 10 ft. lbs. (14 Nm). Note, to avoid damage to the flexible brake line, hold the brake line with a flare nut wrench and spin the brake caliper. If the brake line is sealed to the caliper with a crush washer, replace the crush washer with the appropriate replacement part.

If the caliper bracket was removed
1. Support the caliper temporarily with mechanic's wire taking care to not damage the flexible brake hose.
2. Install the bracket on the knuckle and torque the bolts to:
  
  E30 models: 91 ft. lbs. (123 Nm).
  E36 models: 81 ft. lbs. (110 Nm).
3. Install the brake pads in the caliper bracket as outlined in this section.

Lower the brake caliper over the brake pads.

On E30 models, install a new bolt and torque to 25 ft. lbs. (35 Nm). Check that the pad springs are correctly seated.

On E36 models:
1. Lubricate the slider bolts with an approved brake grease.
2. Install the slider bolts and torque to 18-22 ft. lbs. (25-30 Nm).
3. Install the protective caps and the retainer spring.

If equipped, connect the brake wear sensor wire to the harness. Check for a good connection as most problems with the sensor circuit are caused by faulty connections. Check that the wire is held by the loop in the dust cover and the connector is held at the clips.

Clip the brake fluid line into the holder.

If the brake fluid line was disconnected, bleed the brake system as outlined in this section.

Install the wheels and hand tighten the lug bolts. Lower the vehicle carefully until the tires begin to contact the surface and torque the lug bolts to specification in a crisscross pattern to 66-81 ft. lbs. (90-110 Nm).

WARNING

Failure to properly torque the wheels to the correct torque using the proper sequence could cause a brake pulsation and rotor warpage.

Press the brake pedal down slowly about 2 inches (50mm), then slowly release. Continue to press and release the brake pedal in slow even 2 inch (50mm) strokes until the pedal is firm.

Before servicing the vehicle, refer to the Precautions section.

Draw off brake fluid with a syringe.

Remove or disconnect the following:

Hydraulic brake lines
Wheels
Caliper mounting bolts and disconnect the brake pad wear indicator plug
Caliper assembly

To install:

Install or connect the following:

Brake caliper onto the steering knuckle. Caliper mounting bolt torque for all 3 Series is 63-79 ft. lbs. (85-108 Nm). Caliper mounting bolt torque is 80-89 ft. lbs. (109-121 Nm) for all other models.
Guide bolts to 22-25 ft. lbs. (30-34 Nm)

NOTE

Make sure the brake wear indicator wire is held in the correct position by the tab of the dust cap.

Front wheels

Hydraulic brake system lines and bleed the brake system

Before servicing the vehicle, refer to the precautions in the beginning of this section.

Draw off brake fluid with a syringe.

Disconnect the hydraulic brake lines.

Remove the wheels.

Remove the caliper mounting bolts and disconnect the brake pad wear indicator plug.

Remove the caliper assembly.

To install:

Install the brake caliper onto the steering knuckle. Caliper mounting bolt torque for 3 Series (including the M3 and Z3) is 63-79 ft. lbs. (85-108 Nm).

Caliper mounting bolt torque is 80-89 ft. lbs. (109-121 Nm) for all other models.

Tighten the guide bolts to 22-25 ft. lbs. (30-34 Nm).
NOTE
Make sure the brake wear indicator wire is held in the correct position by the tab of the dust cap.

Install the front wheels.

Connect the hydraulic brake system lines and bleed the brake system.

Disconnect the negative battery cable. Draw off brake fluid with a suitable syringe.

Disconnect the hydraulic brake lines.

Raise and safely support the vehicle. Remove the front tire and wheel assembly.

Remove the caliper mounting bolts and disconnect the brake pad wear indicator plug.

Remove the caliper assembly.

To install:

Install the brake caliper onto the steering knuckle; tighten the caliper mounting bolts to 80-89 ft. lbs. (109-121 Nm). Tighten the guide bolts to 22-25 ft. lbs. (30-34 Nm).
NOTE
Make sure the brake wear indicator wire is held in the correct position by the tab of the dust cap.

Install the front tire and wheel assemblies, then lower the vehicle.

Connect the hydraulic brake system lines.

Connect the negative battery cable, then bleed the brake system.

Before servicing the vehicle, refer to the Precautions section.

Draw off brake fluid with a syringe.

Remove or disconnect the following:

Hydraulic brake lines
Wheels
Caliper mounting bolts and disconnect the brake pad wear indicator plug
Caliper assembly

To install:

Install or connect the following:
NOTE
Make sure the brake wear indicator wire is held in the correct position by the tab of the dust cap.

Brake caliper onto the steering knuckle. Caliper mounting bolt torque for all 3-Series is 63-79 ft. lbs. (85-108 Nm). Caliper mounting bolt torque is 80-89 ft. lbs. (109-121 Nm) for all other models.
Guide bolts to 22-25 ft. lbs. (30-34 Nm)

Front wheels
Hydraulic brake system lines and bleed the brake system