I have a BMW 520i 1992 car .. and here is the problem : it happens when I push the brake pedal .. I feel like something is knocking under my foot .. and sometimes the rear wheels brakes catch unexpectly for a while on slow speeds ..

thank you jturcotte, for replying .. I hope you provide me the instructions to do it myself. thank you jturcotte, for replying .. I hope you provide me the instructions to do it myself.

Well, after taking a closer look, I see you have disc brakes in the rear. So it isn't as obvious what is causing the locking, but usually it's the pads. So, I'm pasting instructions for inspection and pad replacement. Please let me know if you have any questions.


INSPECTION

Check the pad for thickness. The minimum friction material thickness allowed by BMW is 0.08 inches (2.0mm).





Check the condition of the friction material. If the friction
material is cracking or coming loose from the backing plate, replace the
pads.





Check the pattern of wear of the friction material. If the pads
are wearing unevenly or on an angle, there may be a problem with the
caliper hanging up on its slides.





If the inside pad is worn more than the outside pad, the caliper
may not be sliding on the pins. Clean and check for free movement of the
caliper.





If one sides set of pads wear more than the other, the caliper
with the unworn pads may be frozen. Check that the piston retracts
smoothly and that the dust boot is intact.

Fig. Fig. 1: Remove the clip spring before removing the slide pins

Fig. Fig. 2: Remove the caps to expose the internal hex slide pins

Fig. Fig. 3: Make sure the wrench is fully seated in the slide pin to prevent stripping internal hex

Fig. Fig. 4: Inspect the slide pins for corrosion and pitting once removed

Fig. Fig. 5: The inside pad will stay with the caliper and the outside pad will stay with the lower mount

Raise and support the vehicle. Remove the rear wheels.





Disconnect the brake pad wear sensor from the harness.





Carefully pry the pad retainer spring out from the hub side and remove.





Remove the plastic plugs from the caliper slide bolts and remove the bolts. Remove the caliper and the pads from the caliper.

Fig. Fig. 6: Press the piston back in the caliper. Use an old pad to protect the piston when using a C-clamp

Fig. Fig. 7: The inside pad has a spring holding it in the piston bore

Fig. Fig. 8: The upper pad is the outside pad and the lower pad with the spring is the inside pad

Clean the brake caliper and all sliding surfaces. Press the
caliper piston fully back into the caliper housing. Check for leaking
fluid, damaged dust boots and frozen pistons.





Install a new brake pad wear sensor in the pad if the plastic part
has been worn through on the old sensor. New sensors are not required
unless the wire inside the plastic part has been exposed.





Install the brake pads in the caliper. Lower the caliper over the
caliper mount. Install the bolts and torque to 18-22 ft. lbs. (25-30
Nm). Install the retainer spring.





Connect the brake pad wear sensor 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.





Install the wheels and torque to 65-79 ft. lbs. (90-110 Nm).

Well, after taking a closer look, I see you have disc brakes in the rear. So it isn't as obvious what is causing the locking, but usually it's the pads. So, I'm pasting instructions for inspection and pad replacement. Please let me know if you have any questions.

INSPECTION

Check the pad for thickness. The minimum friction material thickness allowed by BMW is 0.08 inches (2.0mm).
Check the condition of the friction material. If the friction material is cracking or coming loose from the backing plate, replace the pads.
Check the pattern of wear of the friction material. If the pads are wearing unevenly or on an angle, there may be a problem with the caliper hanging up on its slides.
If the inside pad is worn more than the outside pad, the caliper may not be sliding on the pins. Clean and check for free movement of the caliper.
If one sides set of pads wear more than the other, the caliper with the unworn pads may be frozen. Check that the piston retracts smoothly and that the dust boot is intact.

REMOVAL & INSTALLATION
See Figures 1 through 8

Fig. Fig. 1: Remove the clip spring before removing the slide pins

Fig. Fig. 2: Remove the caps to expose the internal hex slide pins

Fig. Fig. 3: Make sure the wrench is fully seated in the slide pin to prevent stripping internal hex

Fig. Fig. 4: Inspect the slide pins for corrosion and pitting once removed

Fig. Fig. 5: The inside pad will stay with the caliper and the outside pad will stay with the lower mount

Raise and support the vehicle. Remove the rear wheels.
Disconnect the brake pad wear sensor from the harness.
Carefully pry the pad retainer spring out from the hub side and remove.
Remove the plastic plugs from the caliper slide bolts and remove the bolts. Remove the caliper and the pads from the caliper.

To install:

Fig. Fig. 6: Press the piston back in the caliper. Use an old pad to protect the piston when using a C-clamp

Fig. Fig. 7: The inside pad has a spring holding it in the piston bore

Fig. Fig. 8: The upper pad is the outside pad and the lower pad with the spring is the inside pad

Clean the brake caliper and all sliding surfaces. Press the caliper piston fully back into the caliper housing. Check for leaking fluid, damaged dust boots and frozen pistons.
Install a new brake pad wear sensor in the pad if the plastic part has been worn through on the old sensor. New sensors are not required unless the wire inside the plastic part has been exposed.
Install the brake pads in the caliper. Lower the caliper over the caliper mount. Install the bolts and torque to 18-22 ft. lbs. (25-30 Nm). Install the retainer spring.
Connect the brake pad wear sensor 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.
Install the wheels and torque to 65-79 ft. lbs. (90-110 Nm).