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Probably have a warped or out of round brake rotor or brake drum.
More than likely a front or rear brake rotor is out of round. Depending on what model and year vehicle it could be a brake drum out of round also.
With rear drum brake:-The brake drum may be out of round or may have a rust spot in it. -The brake drum may be cracked.With rear disc brake:-The brake disc may have extreme lateral runout or be mounted improperly. -The brake disc may be cracked. This would be dangerous-Combination of soft brake pads and a directional finish on the disc surface. A directional finish may go away with use and take the noise with it.Regardless of brake type:A brake disc or drum mounted to a bent hub flange or bent axle shaft can cause this noise.
(1) Warped brake rotor (2) an out of round brake drum (3) a warped or damaged brake shoe.
I assume that you have rear drum brake. If so, the knocking sound which happens only when apply the brake is more likely cause by an out-of-round drum. Take your car back to the mechanic that installed them. This problem is not bound to go away.
Brake drums can be resurfaced by turning the brake drum in a brake drum lathe. When the brake drum has deep grooves in it, it cannot be repaired.
A drum brake is a brake that uses friction caused by a set of shoes or pads that press against a rotating drum-shaped part called a brake drum. The term drum brake usually means a brake in which shoes press on the inner surface of the drum.
most likely if you have drum brakes. the shoe has came off the metal mount, and lodged itself in the drum. get new brake shoes. but have fun getting the drum off!!!!!!
Pretty hard to do if you do not have the tools. If you really want to have it checked, then remove the drum and take it to your local garage. Have them turn the drum only a couple of thousands to check it.
A drum brake is a brake that uses friction caused by a set of shoes or pads that press against a rotating drum-shaped part called a brake drum. The term drum brake usually means a brake in which shoes press on the inner surface of the drum.
A blown out rear axle seal will cause grease to leak out into the brake drums
If it is a "used" drum it could have been involved in an impact of some sort. Again if it is a used drum, it may have been "turned" or "refaced" too many times, leaving it out of "true" and too thin. If the drum again is used, it may have been heated during continued stopping and then subjected to water on the road. The drum may simply "warp" thus giving you a pulsation or unequal braking