US3177979A

US3177979A - Shoe centering anchor block

Info

Publication number: US3177979A
Application number: US216129A
Authority: US
Inventors: James J Powlas
Original assignee: Bendix Corp
Current assignee: Bendix Corp
Priority date: 1962-08-10
Filing date: 1962-08-10
Publication date: 1965-04-13
Anticipated expiration: 1982-04-13
Also published as: GB981841A; SE303104B

Description

April 13, 1965 .J. J. PowLAs 3,177,979

SHOE CENTERING ANCHOR BLOCK Filed Aug. 10, 1962 3 Sheets-Sheet 1 INVENTOR.

I JAMES .1. POWLAS.

A T'TORNE Y.

April 13, 1965 J. J. POWLAS 3,177,979

SHOE CENTERING ANCHOR BLOCK Filed Aug. 10, 1962 5 Sheets-Sheet 2 28 30 42 v 40 24 g 26 I f I 32 6 I 34 f3? x/ IE E IN ENTOR.

JAMES J. rwms.

A TTORNEY.

April 13, 1965 J. J. POWLAS 3,177,979

SHOE CENTERING ANCHOR BLOCK Filed Aug. 10, 1962 3 Sheets-Sheet 3 v INVENTOR JAMES J. POWLAS. BY a A 7'TORNEY.

United tats This invention relates to a drum brake and more particularly to an anchor and associated shoe construction.

An object of this invention is to provide a drum brake with means for automatically centering a shoe ring upon retraction from operating position of the brake shoes comprising the shoe ring.

Another object of this invention is to provide a drum brake with means for automatically retracting at least one brake shoe to its normal released center position.

Still another object of this invention is to provide a drum brake with means for effecting a uni-form pressure exerted on the brake shoe by the brake drum.

A further object of the invention is to provide a drum brake with means wherein a shoe ring can conform quite closely to the configuration of drum during brake application.

A still further object of this invention is to provide a drum brake with means wherein once the shoe ring is retracted to normal released center position, bumping or vibration of a moving vehicle, on which the brake is mounted, will not jar the shoe ring from its released center position.

Yet another object of the invention is to provide a drum brake with means wherein once at least one of the shoes is retracted to center position, bumping or vibration of a moving vehicle on which the brake is mounted, will not jar the shoe from its normal released center position.

An overall object of the invention is to accomplish the above objects while obtaining an efficient and improved performance of the brake.

Other objects and features will become apparent from a consideration of the following description wherein se lected example embodiments have been chosen to illustrate the invention. The description proceeds with reference to the accompanying drawings, by way of example only, in which:

FIGURE 1 is a front elevational View of a brake assembly in normal released center position incorporating one embodiment of the present invention;

FIGURE 2 is a View taken along section line 2-2 of FIGURE 1;

FIGURE 3 is a front view of an anchor block of the embodiment of FIGURE 1;

FIGURE 4 is a simplified cutaway view of the anchor block and brake shoe relationship in retracted center position;

FIGURE 5 is a simplified cutaway view of the anchor block and brake shoe relationship during brake application:

FIGURE 6 is a simplified cutaway view of the anchor block and brake shoe relationship during retraction of the brake shoe;

FIGURE 7 is a simplified cutaway view of a modified anchor block and brake shoe relationship shown in normal released center position; and

FIGURES 8, 9 and 10 are simplified cutaway views of different modified anchor block and brake shoe embodiments with their relationship being shown in normal re leased center position.

i ate t Referring to a preferred embodiment of FIGURE 1, a backing plate It} is adapted to be mounted to a stationary part of a vehicle as, for example, a spindle or axle flange. A shoe ring comprises a pair of brake shoes 12 and 14-, having friction linings 13 and 15, respectively, which are slidably mounted on the backing plate and are interconnected at one end by an adjustable strut 16. A spring 18 maintains the web of the brake shoes in contact with the strut 16. A fluid motor 20 is secured to the backing plate between the

other ends

24, 26 of the brake shoes and has movable links 2.2 connected to the webs of each shoe for spreading the same. An anchor pin 28 is connected to the backing plate and an anchor block 30 is rotatably mounted on the pin 28 and has anchoring

surfaces

32 and 34 on which

mating edges

36 and 38 of the

brake shoes

12 and 14 bear in released center position of the shoe ring. A retainer plate 40 is secured to the pin 28 by a snap ring 42 and prevents the

ends

24 and 26 of the brake shoes from moving away from the anchor block in an axial direction. A return spring 44 is connected to each brake shoe for urging and maintaining the shoes in normal released center position. Instead of using the arrangement of spring 44, another conventional arrangement could be used as two springs each having one end connected to the anchor pin and the other end connected to a respective brake shoe. Holddown springs 46 are provided to bias the brake shoes into engagement with the backing plate.

Referring to FIGURE 4, the anchor block and the ends 2 3- and 26 are shown in normal released center position. The curvature of each

edge

32 and 34 is of the same radius R with the center points a and [2 thereof being offset from the center 0 of the anchor pin 28. The

edges

36 and 38 of the brake shoes are of the same radius and center points as the

edges

32 and 34 of the anchor block. if the shoe 14 moves or floats vertically upward, the center point b of bearing edge 38 moves upwardly. Since the edge 38 and surface 34 are of the same curvature and are circumscribed about the same center point, the center points of each must coincide for there to be full engagement of edge 38 with surface 34. The center point b of surface 34 will move upward upon rotation of the block St; in a clockwise direction since the block rotates about the center c of the pin 23. Thus, any vertical movement by the brake shoe 14 will reflect in rotation of the anchor block and the brake shoe 14 may be said to float with respect to the pin-28 or walk up the anchor block. If the shoe 14 is forced vertically downward, the anchor block will rotate counterclockwise. This may be referred to as the shoe is walking down the anchor block. Conversely, any rotation of the anchor block with simultaneous rotation of the shoe 14 will reflect in vertical movement of the shoe 14. Shoe 12 and anchor block 30 will have the same association as shoe 14 and anchor block 30 when the edge 36 fully engages the bearing surface 32. It should also be noted that the position of one shoe determines the position of the other shoe since vert-ical movement of one shoe in one direction effects rotation of the anchor block and thereby effects vertical movement in the opposite direction of the other shoe.

Operation Upon actuation of the brake the fluid motor 28 spreads the

shoe ends

24 and 26 away from the anchor block until the friction linings i3 and 15 engage the brake drum 48. Assuming rotation of the drum in the direction of arrow A,

brake shoes

12 and 14 will be the primary and secondary brake shoes, respectively. The drum will force the end 26 of the secondary brake shoe 14 back in engagement with its anchor block surface 34 and the shoe ends will take the position illustrated in FIGURE 5. If there is more pressure on one spot of the brake lining (due to a high spot on the lining or due to deformation of the drum during brake application) than on another, for instance, as at B, the shoe will be able to float with respect to the pin 28 or walk up the anchor block in the direction of arrow C with the point e of the web of the brake shoe which is aligned with the horizontal center line of the pin 28 moving a vertical distance D above the center of the pin 28. Each point of the edge 33 will have moved the same vertical distance D with respect to the horizontal center line. When the shoe walks up the anchor block 30, the edge 38 of the shoe will slide vertically upward on the anchor surface 34- and always the in engagement with the anchor surface 3 with the anchor block turning in a clockwise direction. The shoe 14 walks up the anchor block until it reaches the position wherein the force exerted on the shoe 14 by the drum 48 is substantially equally distributed. The anchor block will have rotated at least through an angle F". If [pressure in the fluid motor is decreased, the brake drum and brake shoes will tend to return to their normal shapes from their deformed shapes during brake actuation and due to this, the drum and the return spring 44 will force the secondary shoe to walk down the anchor block thereby rotating the anchor block toward its normal released position.

Upon release of the brake shoes, the secondary shoe 14 will walk down the anchor block back to its normal released position by sliding vertically downward on the bearing surface 34. The anchor block 30 will be rotated simultaneously back to its normal released position. However, if the secondary shoe 14 tends to drag and will not return to its normal released position as shown in FIGURE 4, then the anchor block still must revolve through an angle G before returning to normal released position. During retraction of shoe 12, the end 24 will move in the direction of arrow H with the point I of the edge 36 of shoe 12 striking the surface 32 of the anchor block thereby rotating the anchor block counterclockwise until the edge 36 of shoe 12 fully engages the surface 32. When the anchor block is rotated counterclockwise by the shoe 1-2, the edge 38 of shoe 14 will still fully engage the bearing surface 34 and rotational motion .of the anchor block will result in automatically forcing the secondary shoe 14 downwardly to its normal released position resulting in the shoe ring being automatically recentered.

If, for instance, during actuation of the brake the shoe 14 had been forced vertically downward by the drum 48 and the anchor block had rotated counterclockwise then the .point K of shoe 12 would first engage the bearing surface 32 thereby rotating the anchor block clockwise drum will act on the shoes at the dragging locations to force the shoe ring into its normal released center position. :For instance, if the shoe 14- was dragging near the anchor block and the shoe 12 was dragging near the adjustable strut 1 6, the drum will strike these points to force the shoe 12 upwards and the shoe 14- downward-s effecting rotation of the anchor block through the remaining portion of G. Since vertical movement of one shoe in one direction eifects vertical movement of the other shoe in the opposite direction, the action of the drum on one shoe helps to automatically center both shoes. Since the drum acts on both hoes during a single revolution, the drum acts twice in a single revolution to center the shoe ring to its normal released position.

Due to the curvature of the anchor block bearing surfaces and their respective brake shoe edges the shoe ring is locked in vertical position during normal released position thus assuring that during bumping and vibration of the vehicle neither shoe moves vertically to drag against the drum. 7

Obviously, if the drum d8 rotates in the direction opposite to arrow A, shoe 12 will be the secondary shoe and will associate with the anchor block 30 in the same manner as shoe 14 does when the drum rotates in the direction of arrow A.

Referring to FIGURE 7, a modified anchor block 5% is shown. The anchor block 5% has a bearing surface 52 defining an arc whose radius is larger than the radius of the arm defined by its other bearing surface 54. A pair of brakes shoes as and 58 have

mating bearing edges

60 and 62, respectively, which are of the same radius as their respective bearing edges. Since the center point of the are 54 is at the center of the pin 28, only the shoe 53 will be able to walk up or walk down the anchor block. Vertical movement of shoe 58 will result in rotation of the anchor block, but the rotation thereof will not efiect vertical movement of the shoe 56. Once the shoes 5s and 58 are centered in normal released position, the shoes will be locked from vertical movement.

Referring to the embodiment of FIGURE 8, there is illustrated an anchor block 63 having a bearing surface 64 defining an arc of a given radius and a flat bearing surface es. A pair of brake shoes 68 and 79 have mating bearing edges shaped to fully engage the anchor block during normal released position with the bearing edge 72 of the shoe 68 defining an arc of the same radius and center point as the bearing surface 64 and the bearing edge 74 being flat and at an angle complementary to the bear ing surface 66. The brake wherein this modification is utilized will operate in the same manner as that of FIG- URE l with only the secondary shoe 68 walking up or walkingdown the anchor block and being automatically retracted to its normal released center position and being locked from vertical movement while in normal released center position.

Referring to the embodiment of FIGURE 9, there is illustrated an anchor block 76 similar to the anchor block 63 of FIGURE 8; A pair of brake shoes 7% and 89 have located at the outer ends of

edges

79 and 81 hearing edges 82 and 84, respectively, bearing on the anchor block hearing surfaces 86 and 38 in shoe release position. The hear- .ing edges 82 are of the same radius and have the same center point of circumscription as the bearing surface 86 of the anchor block. The brake shoe and anchor block relationship during operation will be the same as the embodiment of FIGURE 8.

7 Referring to the embodiment of FIGURE 10, another modification is illustrated wherein an anchor block 9@ has a pair of convexly shaped bearing surfaces 91 and 92 circumscribing an arc of a given radius R and their respective mating shoe (93, 94) and bearing edges 95 and 96 circumscribing an arc of the some radius about the same center point as their respective bearing surfaces. The operation of this embodiment is the same as that of the embodiment of FIGURE 1 only when the

shoe

93 or 94 walks down the anchor block 96 the anchor block will rotate clockwise or counterclockwise, respectively, and when the shoe 93 or 9d walks up the block 90, the block will rotate counterclockwise or clockwise, respectively. The shoes will be automatically retracted to released cen ter position and the shoe ring will be locked from vertical movement during vehicle movement while in released position. Obviously, the bearing surface arcs may be of the same radius or of different radii or the anchor block may have one straight edge and one curved as shown in the previous embodiments.

While the invention has been illustrated with a particuular type of drum brake, it can readily be seen that the invention may be utilized with other types of drum brakes, Numerous adaptations of the invention, in addition to those illustrated, will be obvious to those skilled in the art. It is my intention to include within the scope of the following claims all equivalent applications of the invention whereby the same or substantially the same results may be obtained.

I claim:

1. In a drum brake, a support, brake shoes slidably mounted and arranged in end-to-end relationship on said support, an anchor block rotatably mounted on said support between a pair of adjacent ends of said shoes, means for actuating said shoes, means for retracting said shoe ends against said anchor block, said adjacent ends of said shoes having bearing edges, said anchor block having bearing surfaces for engagement with a respective bearing edge of each of said adjacent ends of said shoes, at least one of said bearing surfaces of said anchor block forming a curve, the center of curvature of said one hearing surface being offset from the center of rotation of said anchor block, the respective shoe bearing edge of said at least one anchor block bearing surface being so shaped that at least the outer portions thereof will simultaneously engage any portions of said at least one anchor block hearing surface in any position of said anchor block during brake actuation while the drum is rotating in one direction and simultaneously engage portions of said anchor block bearing surface during shoe release position, the other of said shoe and bearing edges being so shaped that at least the outer portions thereof are capable of simultaneously engaging a respective portion of its respective bearing surface of said anchor block when in released position whereby at least said shoe having the bearing edge engaging said cnrved bearing surface of said anchor will be automatically centered in released position.

2. In a drum brake, a support, brake shoes slidably mounted and arranged in end-to-end relationship on said support, an anchor block rotatably mounted on said support between a pair of adjacent ends of said shoes, means for actuating said shoes, means for retracting said shoe ends against said anchor block, said adjacent ends of said shoes having bearing edges, said anchor block having hearing surfaces for engagement with a respective bearing edge of each of said adjacent ends of said shoes, at least one of said bearing surfaces of said anchor block forming a curve, the center of curvature of said one bearing surface being ofiset from the center of rotation of said anchor block, the respective shoe bearing edge of said at least one anchor block bearing surface being so shaped that substantially the entire edge will engage at least any portion of said at least one anchor block bearing surface in any position of said anchor block during brake actuation while the drum is rotating in one direction and engage at least a portion of said anchor block bearing surface during shoe release position, the other of said shoe end hearing edges being so shaped that at least each outer portions thereof is capable of engaging simultaneously any respective portion of its respective bearing surface of said anchor block when in released position whereby at least said shoe having the bearing edge engaging said curved bearing surface of said anchor block will be automatically centered in released position.

3. In a drum brake, a support, brake shoes slidably mounted and arranged in end-to-end relationship on said support, an anchor block rotatably mounted on said support between a pair of adjacent ends of said shoes, means for actuating said shoes, means for retracting said shoe ends against said anchor block, said adjacent ends of said shoes having bearing edges, said anchor block having bearing surfaces for engagement with a respective bearing edge of each of said adjacent ends of said shoes, at least one of said bearing surfaces or" said anchor block forming a curve, the center of curvature of said one bearing surface being oifset from the center of rotation of said anchor block, the respective shoe bearing edge of said at least one anchor block bearing surface being so shaped that substantially the entire edge will engage at least any portion of said at least one anchor blOCli bearing surface in any position of said anchor block during brake actuation while the drum is rotating in one direction and engage at least a portion of said anchor block bearing surface during shoe release position, the other of said shoe end bearing edges being so shaped that substantially the entire edge will engage at least a portion of its respective bearing surface of said anchor block when in released position whereby at least said shoe having the bearing edge engaging said bearing surface of said anchor block defining said are will be automaticaily centered in released position.

4. In a drum brake, a support, brake shoes slidably mounted and arranged in end-to-end relationship on said support, an anchor block rotatably mounted on said support between a pair of adjacent ends of said shoes, means for actuating said shoes, means for retracting said shoe ends against said anchor block, said adjacent ends of said shoes having bearing edges, said anchor block having hearing surfaces for engagement with a respective bearing edge of each of said adjacent ends of said shoes, at least one of said bearing surfaces of said anchor block forming an arc of a predetermined radius, the center of said radius being offset from the center of rotation of said anchor block, the respective shoe bearing edge of said at least one anchor block bearing surface being so shaped that at least the outer portions thereof each form an arc of the same radius and will simultaneously engage any portion of said at least one anchor block bearing surface in any position of said anchor block during brake actuation while the drum is rotating in one direction and simultaneously engage portions of said anchor bearing surface during shoe release position, the other of said shoe end bearing edges being so shaped that at least each outer portion thereof is capable of engaging simultaneously any respective portion of its respective bearing surface of said anchor block when in released position whereby at least said shoe having the bearing edge engaging said bearing surface of said anchor block forming an arc Will be automatically centered in released position.

5. In a drum brake, a support, brake shoes slidably mounted and arranged in end-to-end relationship on said support, an anchor block rotatably mounted on said support between a pair of adjacent ends of said shoes, means for actuating said shoes, means for retracting said shoe ends against said anchor block, said adjacent ends of said shoes having bearing edges, said anchor block having hearing surfaces for engagement with a respective bearing edge of each of said adjacent ends of said shoes, at least one of said bearing surfaces of said anchor block forming an arc of a predetermined radius, the center of said radius being offset from the center of rotation of said anchor block, the respective shoe bearing edge of said at least one anchor block bearing surface having a curve of sub stantially the same radius so that substantially the entire edge will engage at least any portion of said at least one anchor block bearing surface in any position of said anchor block during brake actuation while the drum is rotating in one direction and engage at least a portion of said anchor block bearing surface during shoe release position, the other of said shoe end bearing edges being so shaped that at least each outer portion thereof is capable of engaging simultaneously any respective portion of its respective bearing surface of said anchor block when in released position whereby at least said shoe having the bearing surface engaging said bearing surface of said anchor block defining an arc will be automatically centered in released position.

6. In a drum brake, a support, brake shoes slidably 7 V mounted and arranged in end-to-end relationship on said support, an anchor block rotatably mounted on said support between a pair of adjacent ends of said shoes, means for actuating said shoes, means for retracting said shoe ends against said anchor block, said adjacent ends of said shoes having bearing edges, said anchor block having bearing surfaces for engagement with a respective bearing edge of each of said adjacent ends of said shoes, at least one of said bearing surfaces of said anchor block forming an arc of a predetermined radius, the center of said radius being oflfset from the center of rotation of said anchor. block, the respective shoe bearing edge of said at least one anchor block bearing surface a curve of substantially the same radius so that substantially the entire edge will engage at least any portion of said at least one anchor blockbearing surface in any position of said anchor block during brake actuation while the drum is rotating in one direction and engage at least a portion of said anchor block bearing surface during shoe release position, the other of said shoe end bearing edges being so shaped that its entire edge will engage at least a portion of its respective bearing surface of said anchor block when in released position whereby at least said shoe having the bearing surface engaging said bearing surface of said anchor block forming an arc will automatically centered in released position.

7. In a drum brake, a support, brake shoe slidably mounted and arranged in end-to-end relationship on said support, an anchor block rotatably mounted on said support between a pair of adjacent ends of said shoes, means for actuating said shoes, means for retracting said shoe ends against said anchor block, said adjacent ends of said shoes having bearing edges, said anchor block having bearing surfaces for engagement with a respective bearing edge of each of said adjacent ends of said shoes, one of said bearing surfaces of said anchor block forming an arc of a predetermined radius, the center of said radius being offset from the center of rotation of said anchor block, the respective shoe bearing edge of said one anchor block bearing surface being so shaped that at least the outer portions thereof each form an arc of substantially the same radius and will simultaneously engage any portion of said one anchor block bearing surface in any position of said anchor block during brake actuation while the drum is rotating in one direction and simultaneously engage portions of said one anchor block bearing surface during shoe release position, the other of said bearing surfaces of said anchor block forming an arc of a predetermined radius, the center of said last named radius being ofiset from the center of rotation of said anchor block, the other of said shoe end bearing edges being so shaped that at least the outer portions thereof each form an arc of the same last mentioned radius and is capable of simultaneously engaging any portion of said other anchor block bearing surface in any position of said anchor block during brake actuation while the drum is rotating in the other direction and simultaneously engaging portions of said other anchor block bearing surfaces during shoe release position whereby said shoe will be automatically centered in released position.

8. In a drum brake, a support, brake shoe slidably mounted and arranged in end-to-end relationship on said support, an anchor block rotatably mounted on said support between a pair of adjacent ends of said shoes, means for actuating said shoes, means for retracting said shoe ends against said anchor block, said adjacent ends of said shoes having bearing edges, said anchor block having bearing surfaces for engagement with a respective bearing edge of each of said adjacent ends of said shoes, one of said bearing surfaces of said anchor block forming an arc of a predetermined radius, the center of said radius being offset from the center of rotation of said anchor block, the respective shoe bearing edge of said one anchor block bearing surface having a curve of substantialiy the same radius so that substantially the entire edge will engage at least any portion of said one anchor block bearing surfacein any position of said anchor block during. brake actuation while the drum is rotating in'the other di-' rection and engage at least a portion of said one anchor block bearing surface during shoe release position, the other of said bearing surfaces of said anchor block forming an arc of a predetermined radius, the center of said named radius being offset from the center of rotation of said anchor block, the other of said shoe end bearing edges being so shaped that at least the outer portions thereof each form an arc of the same last mentioned radius and is capable of simultaneously engaging any portion of said other anchor block bearing surface in any position of said anchor block during brake actuation while the drum is rotating in one direction and simultaneously engaging portions of said other anchor block bearing surface during shoe release position, whereby said shoes will be automatically centered in released position.

9. In a drum brake, a support, brake shoes slidably mounted and arranged in end-to-end relationship on said support, an anchor block rotatably mounted on said support between a pair of adjacent ends of said shoes, means for actuating said shoes, means for retracting said shoe ends against said anchor block, said adjacent ends of said shoes having bearing edges, said anchor block having bearing surfaces for engagement with a respective bearing edge of each of said adjacent ends of said shoes, one of said bearing surfaces of said anchor block forming an arc of a predetermined radius, the other of said bearing surfaces of said anchor block forming an arc of a predetermined radius, the center of each of said radii being offset from the center of rotation of said anchor block, the respective edges of said brake shoes each forming an arc of the same predetermined radius as its respective anchor bearing surface so that substantially the entire bearing edge of each said brake shoe will engage at least a portion of its respective anchor bearing surface in any position of said anchor block during brake actuation, depending on the direction of rotation of said drum, and engage at least a portion of its respective anchor block surface during shoe release position whereby said shoes will be automatically centered in released position.

10. The structure as recited in claim 7 wherein said anchor block bearing surfaces are of the same predetermined radius.

11. The structure as recited in claim 7 wherein the distance between the center of rotation of said anchor block and any portion of said anchor block bearing surfaces is less than either of the radii of curvature of said anchor block bearing surfaces.

12. The structure as recited in claim 7 wherein each anchor block bearing surface is located between its respective center point of circum'scription and the center of rotation of said anchor block.

13. The structure as recited in claim 7 wherein the center of rotation of said anchor block is located between each anchor block bearing surface and its respective cener point of circumscription.

14. The structure as recited in claim 4 wherein the center of rotation of said anchor block is located between said at least one anchor block bearing surface and its respective center point of circumscription.

15. The structure as recited in claim 4 wherein said at least one anchor 'block bearing surface is located between its respective center point of circumscription and the center of rotation of said anchor'block.

16. The structure as recited in claim 13 wherein the distance between the center of rotation of said anchor block and any portion of said anchor block bearing surfaces is less than either of the radii of curvature of said anchor block bearing surfaces.

17. The structure as recited in claim 14 wherein the distance between the center of rotation of said anchor block and any portion of said one anchor block bear- ReEerences Cited by the Examiner UNITED STATES PATENTS 11/36 La Brie 188-7835 X 4/56 Brooks 188-78.35

Schnell 188-7835 Dombeck 188-206 X Parker 188-78 Nash 188-7835 Borgard 188-7835 ARTHUR L. LA POINT, Primary Examiner.

Claims

1. IN A DRUM BRAKE, A SUPPORT, BRAKE SHOES SLIDABLY MOUNTED AND ARRANGED IN END-TO-END RELATIONSHIP ON SAID SUPPORT, AN ANCHOR BLOCK ROTATABLY MOUNTED ON SAID SUPPORT BETWEEN A PAIR OF ADJACENT ENDS OF SAID SHOES, MEANS FOR ACTUATING SAID SHOES, MEANS FOR RETRACTING SAID SHOE ENDS AGAINST AND ANCHOR BLOCK, SAID ADJACENT ENDS OF SAID SHOES HAVING BEARING EDGES, SAID ANCHOR BLOCK HAVING BEARING SURFACES FOR ENGAGEMENT WITH A RESPECTIVE BEARING EDGE OF EACH OF SAID ADJACENT ENDS OF SAID SHOES, AT LEAST ONE OF SAID BEARING SURFACES OF SAID ANCHOR BLOCK FORMING A CURVE, THE CENTER OF CURVATURE OF SAID ONE BEARING SURFACE BEING OFFSET FROM THE CENTER OF ROTATION OF SAID ANCHOR BLOCK, THE RESPECTIVE SHOE BEARING EDGE OF SAID AT LEAST ONE ANCHOR BLOCK BEARING SURFACE BEING SO SHAPED THAT AT LEAST THE OUTER PORTIONS THEREOF WILL SIMULTANEOUSLY ENGAGE ANY PORTIONS OF SAID AT LEAST ONE ANCHOR BLOCK BEARING SURFACE IN ANY POSITION OF SAID ANCHOR BLOCK DURING BRAKE ACTUATION WHILE THE DRUM IS ROTATING IN ONE DIRECTION AND SIMULTANEOUSLY ENGAGE PORTIONS OF SAID ANCHOR BLOCK BEARING SURFACE DURING SHOE RELEASE POSITION, THE OTHER OF SAID SHOE AND BEARING EDGES BEING SO SHAPED THAT AT LEAST THE OUTER PORTIONS THEREOF ARE CAPABLE OF SIMULTANEOUSLY ENGAGING A RESPECTIVE PORTION OF ITS RESPECTIVE BEARING SURFACE OF SAID ANCHOR BLOCK WHEN IS RELEASED POSITION WHEREBY AT LEAST SAID SHOE HAVING THE BEARING EDGE ENGAGING SAID CURVED BEARING SURFACE OF SAID ANCHOR WILL BE AUTOMATICALLY CENTERED IN RELEASED POSITION.