What Is a Brake Expander?

Typically, a BRAKE EXPANDER is a hydraulic device that exerts hydraulic pressure on the linings of a brake drum. As such, it is a useful tool for boosting the braking power of a vehicle's braking system. A typical expander is used on drum brakes, where the brake drum expands and contracts radially. This radial expansion translates into alignment changes along the brake drum's axis.

A BRAKE EXPANDER consists of a cylinder housing containing two coaxial pressure pistons. The cylinder's axis is parallel to the axis of the brake drum. Two adjusting screws threaded into the pistons, one for each piston, transmit movement to the flange members of a respective brake shoe. A bent spring piece is threaded onto the flange of the adjusting screw, and has an opening which exposes the pressure piece's groove. The flange member of the brake shoe engages the groove of the pressure piece, and a thrust member attached to the brake support serves to maintain this engagement.

The cylinder housing is augmented by a pair of retraction springs 18, which are used to pull the adjusting screws out of their threaded holes. The retraction springs are a bit of a red herring in that they do not affect braking performance. The expander is assembled using a bent spring piece, which is a good idea since efficiency is of the essence in this application. The flange member is also an important part of the expander's assemblage. The flange member is attached to the brake support 10 by a thrust member.

A BRAKE EXPANDER also includes two pressure pieces, one of which is the most important. The flange member engages the corresponding groove of the pressure piece, and serves to press the brake linings against the brake drum's interior. The pressure piece may be comprised of a spherical inner end and a flange member, or it may be a composite of the two. A corresponding matching pressure piece is inserted into the spherical indentation on the end face of the adjusting screw. This is the largest and most cumbersome of the components. The pressure piece's other important job is to impress the brake linings on the brake drum.

The flange member is accompanied by the corresponding spherical indentation on its end face, and a matching spherical indentation on that of the adjusting screw. The flange member of the brake shoes is slidably engaged with the radial groove of the pressure piece, and serves to impress the brake linings on the drum's interior. The corresponding spherical indentation is the best part of the flange member. The spherical indentation on both the end faces of the adjusting screws and the flange member of the brake shoe also performs the aforementioned small-scale miracles. Lastly, the flange member of the brake shoe is also a good idea since it serves to impress the brake linings on a brake drum's interior. The flange member of the brake Shoe also has the fender-mood-worthy magnetic linings.