GB2275086A - Reversing drum brake - Google Patents

Abstract

A reversing drum brake 1 comprises brake shoes 7, 8 and a collapsing mechanism 8 having pivotally mounted cranked members 20, 21 which engage respective brake shoe web members 2, 3. The members 20, 21 cooperate with one another by means of a pin 41 slidably engaging slot 40. In normal braking under forward motion (arrow 50), the pin 41 is urged against the bottom of slot 40 and web members 2, 3 are urged outwardly to effect braking. In braking under reverse motion (arrow 51), the pin 41 slides upwardly within slot 40 and members 20, 21 move inwardly, thereby allowing brake web members 2, 3 to move inwardly into a "collapsed" state. A self-adjusting device 4 (see Figs. 4 and 5) is also described which includes an adjuster screw 68 arranged to be screwed outwardly by an indexing finger 70 when the brake shoes have worn a predetermined amount. A cable 79 extends between indexing finger 70 and cranked member 20 and is arranged to disengage finger 70 from engagement with adjuster screw 68, when the brake is in a collapsed state. <IMAGE>

Description

VEHICLE CONPONENT This invention relates to a vehicle component and particularly, although not exclusively, to a reversing drum brake. A collapsing mechanism for a reversing drum brake and a self-adjusting device for a collapsible reversing drum brake are described.

Reversing drum brakes are of use particularly in relation to trailers which are pulled by a towing vehicle.

When the towing vehicle decelerates, so-called "overrun" brakes on the trailer operate automatically so as to reduce the speed of the trailer in a controlled manner.

However, such overrun brakes also tend to operate automatically when the trailer is reversed.

Solutions to this problem include the provision of a means for rendering the overrun brakes ineffective during reversing movement. For example, GB 2 053 391 and EP 0 253 463 provide collapsing mechanisms between opposing ends of a pair of brake shoes, the mechanisms being arranged to reduce the distance between the brake shoes during reversing and thereby reduce or eliminate altogether their braking effect on a brake drum. However, such mechanisms may not be simple to manufacture and, furthermore, often require a substantial "roll-off" force by the towing vehicle to enable the brakes to collapse inwards when reversing.

Preferred embodiments of the present invention aim to provide an improved collapsing mechanism for a reversing drum brake.

According to one aspect of the present invention, there is provided a reversing drum brake comprising a collapsing mechanism, the mechanism comprising a first control member operatively connected to a brake shoe, guide means being provided for guiding travel of said control member so as to control travel of said brake shoe between a first position and a second position spaced inwardly from said first position, the arrangement being such that when a force is applied in a first direction to said control member travel of said control member is guided by said guide means and said brake shoe moves towards said second position.

The mechanism preferably comprises first and second control members operatively connected to a pair of brake shoes. Said guide means is preferably arranged to guide the travel of one of said control members relative to the other so as to control travel of at least one of said brake shoes between said first position and said second position. Preferably, the arrangement of the reversing drum brake is such that when a force is applied in said first direction to one of said control members, said control member is guided as aforesaid and when a force is applied in a second direction to one of said control members, at least one brake shoe is urged towards said second position.

Preferably, said first and second directions are substantially opposite to one another.

Said control members (when provided) are preferably operatively connected adjacent to respective first opposing ends of said brake shoes. A braking device, for example, an expander device is preferably provided between respective second opposing ends of said brake shoes. Said force may be applied in said first and/or said second directions to said control members by operation of said braking device.

Preferably, each of said brake shoes is arranged to travel between respective first and second positions as aforesaid. Preferably, a first element of said guide means is provided by said first control member and a second element of said guide means is arranged to cooperate with said first element and is provided by said second control member. Preferably, the or each control member is so guided by said guide means that, in use, an end of the or each control member moves in a generally radial direction. Where first and second control members are provided, said control members may be arranged so that, in use, the movement of the first control member generally mirrors the movement of the second control member, the control members being disposed on the respective opposite sides of a radius of a respective brake drum.

Preferably, said guide means is arranged to provide guided sliding movement. Said guide means may comprise a guide track defined by said first control member and a guide member which is suitably provided on said second control member and is arranged to cooperate with said guide track. Preferably, said guide track comprises a slot in said first control member. Said guide member may comprise a projecting member.

Preferably, the or each of said control members includes an abutment means arranged to cooperate with a respective brake shoe or a part connected thereto (for example, a brake shoe support member), to operatively connect the respective said control member to the respective brake shoe. Said first control member may be mounted for pivotal movement about a first fixed point.

Said second control member (when provided) may be mounted for pivotal movement about a second fixed point. Said first and second fixed points may be disposed diametrically opposite to one another.

Preferably, said first control member is elongate.

Said first control member may be generally curved in shape. Preferably, said second member (when provided) is elongate. Said second member may be generally curved in shape. A part of the or each brake shoe may be arranged to be sandwiched between parts of a respective one of said control members.

A biasing means, for example a resilient means in the form of a tension spring is preferably provided for biasing said first and/or said second control members towards said first position.

The invention extends to a collapsing mechanism as described in any statement herein for a reversing drum brake, per se.

Additionally, it is appreciated in the trailer industry that, for many applications, relatively high performance trailer brakes are required, in comparison to, for example, car drum brakes of similar size. In use, trailer brake shoes are prone to wear relatively rapidly.

It is, therefore, preferable to have an automatic selfadjusting mechanism for the brake so as to reposition worn shoes closer to the brake drum and thereby maintain braking efficiency throughout the life of the shoes, without the need for regular manual adjustment.

However, in the case of a trailer fitted with, for example, a collapsing drum brake, it is difficult to design an automatic self-adjusting mechanism, since the collapse of the brake during reversing of the trailer would tend to manifest itself in the same manner as worn brake shoes; both would result in brake shoes being disposed at a position spaced from the brake drum and thus, the self-adjusting mechanism would operate unnecessarily when the brakes collapsed.

Preferred embodiments of the invention aim to improve upon this situation by providing a self-adjusting mechanism arranged to alleviate these problems.

According to a second aspect of the invention, there is provided a reversing drum brake comprising a selfadjusting device, the self-adjusting device comprising a first member and a second member operatively connected between opposing ends of a pair of brake shoes of the brake, adjuster means provided for adjusting the distance between said first and second members, wherein said adjuster means is operable to increase automatically said distance when the distance between at least one of said brake shoes and a brake drum is greater than a predetermined distance.

Said adjuster means is preferably arranged to operate to increase automatically said distance when a vehicle which includes said reversing drum brake is travelling in the forward direction. Said adjuster means is preferably arranged to operate to increase automatically said distance during and/or immediately following operation of the reversing drum brake to retard the vehicle.

Said first member is preferably operatively connected to an end of one of said brake shoes. Preferably said first member is directly connected to a brake shoe web member which carries a said brake shoe. Said first member may be screw-threadedly mounted. In this case, preferably said adjuster means is arranged to cause said first member to be screwed outwardly in order to increase the distance between said first and second members. Said first member preferably includes one of either a screw-threaded shaft or a screw-threaded socket, said shaft or socket being arranged to co-operate with the other one of either a screw-threaded shaft or screw-threaded socket of the selfadjusting device. Said other shaft or socket is preferably a component of an indexing member. Said indexing member is preferably rotatably mounted in a housing of said selfadjusting device.Said indexing member preferably includes a plurality of indexing elements, for example, in the form of ratchet teeth. The elements are preferably equidistantly spaced apart. The self-adjusting device is preferably arranged such that rotation of said indexing member within said housing causes said first member to be screwed outwardly in order to increase the distance between said first and second members.

An indexing member actuator means is preferably provided and arranged to cause said indexing member to rotate within said housing. Said indexing member actuator means is preferably arranged to pivot between first and second positions in order to cause rotation of said indexing member. Said self-adjusting device is preferably arranged such that movement of said indexing member between said first and second positions is only caused when the distance between said at least one shoe and said brake drum is greater than said predetermined distance.

Said indexing member actuator means is preferably pivotally mounted on said aforementioned housing within which said indexing member is disposed. A first link means is preferably connected between said indexing member actuator means and one of said brake shoes. Said first link means is preferably rigid.

Said second member preferably comprises a lever means. Said lever means is preferably pivotally mounted (suitably within said aforementioned housing, when provided). Said lever means is preferably connected to an operating member (for example, a cable of an overrun brake) so that operation of said operating member causes pivotal movement of said lever means thereby to cause said pair of brake shoes to move towards the brake drum to effect braking.

Preferably, means is provided for rendering the adjuster means inoperative when a vehicle which includes said reversing drum brake is travelling in a reverse direction. Preferably, said adjuster means is arranged to be inoperative when said reversing drum brake is in a collapsed state.

A link means, for example, a cable, is preferably provided between said adjuster means and a part of the collapsing mechanism of the reversing drum brake. Said link means is preferably arranged to render inoperable said aforementioned indexing member actuator means (when provided). Preferably, said link means is arranged to retract said indexing member actuator means from a position in which it is able to effect rotation of said indexing member to a position in which it is unable to effect rotation of said indexing member.

The invention extends to a self-adjusting device as described in any statement herein for a reversing drum brake, per se.

The invention extends to a reversing drum brake including any of the features of the reversing drum brake according to the first and second aspects.

Specific embodiments of the present invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which : Figure 1 is a side elevation, partly in crosssection, of a part of a reversing drum brake; Figure 2 is a sectional view taken on line A-A of Figure 1; Figure 3 is a sectional view taken on line B-B of Figure 1; Figure 4 is a perspective view of an expander device; and Figure 5 is an exploded view of the expander device of Figure 4.

In the Figures like reference numerals denote like or corresponding parts throughout.

A reversing drum brake 1 comprises opposing arcuate brake shoe web members 2, 3 having brake shoes 7, 8 thereon. The brake shoes 7, 8 are arranged to engage opposite sides of a brake drum (not shown) to effect braking. The expander device 4 engages respective top ends 5, 6 of the brake shoe web members 2, 3, the expander device being operable to expand and contract. When expanded the expander device urges the shoes 2, 3 outwards so as to engage the brake drum and effect braking. A collapsing mechanism 9 is provided adjacent lower ends 10, 11 of the brake web members 2, 3. The collapsing mechanism 9 is arranged to collapse when a trailer incorporating the reversing drum brake 1 is reversed.

In detail, the reversing drum brake 1 comprises a supporting back plate 12 which supports the brake members 2, 3. A tension spring 75 is arranged between the brake shoes 2, 3 so as to keep the shoes 7, 8 away from the brake drum when the brakes are not operating. The expander device 4 may be of any suitable form, being actuable by a brake linkage (not shown) of an overrun mechanism, to urge the ends 5, 6 outwardly in order to cause brake shoes 7, 8 to engage the brake drum and effect braking.

The collapsing mechanism 9 of the brake 1 comprises two cranked members 20, 21 which are pivoted upon respective spindles 22, 23 mounted on the back plate 12.

The cranked members 20, 21 may be of sandwich construction, the member 20 comprising spaced apart parts 25,26 and the member 21 comprising spaced apart parts 27, 28. The brake shoe web member 2 fits between parts 25, 26 of the member 20 and the brake shoe web member 3 fits between parts 27, 28 of member 21. The brake shoe web members 2, 3 are cut away in the region of the spindles 22, 23 in order to accommodate the spindles.

Abutments 30, 31 are fixed to respective members 20, 21. The abutments 30, 31 include respective arcuate bearing surfaces 32, 33 which are arranged to abut against the lower ends 10, 11 of the brake shoe web members 2, 3.

A spring 35 is fixed at one of its ends to the abutment 30 and at its other end to the back plate 12.

The cranked member 21 includes an angled guide slot 40 in each of its parts 27, 28. A pin 41 is fixed to the cranked member 20 adjacent an end thereof. The pin 41 is slidably received in the slots 40 in the cranked member 21. Adjacent the slots 40 and pin 41, the parts 25, 26 are bent outwardly so that parts 27, 28 can fit therebetween as seen in Figure 2.

The slots 40 are suitably angled at an acute angle in a range up to 45 relative to a radius through pin 41 and centre 45 of the brake 1 when the collapsing mechanism is in non-collapsed state, as shown in Figure 1.

The reversing drum brake 1 operates as follows, during normal braking under forward motion in an anticlockwise direction as indicated by arrow 50.

As a towing vehicle brakes, a known overrun coupling (not shown) pulls on a brake cable (not shown) which acts on expander device 4 so as to cause it to apply an outward force to the top ends 5, 6 of respective brake shoe web members 2, 3. This causes brake shoe web member 3 to be pushed anti-clockwise around the brake drum (not shown) causing an anti-clockwise force to be applied to abutment 31 and, in turn, an anti-clockwise force is applied to member 21. An anti-clockwise force is then applied by member 21 to the pin 41 located towards the bottom of slot 40 as seen in Figure 1, the pin in turn applying an anticlockwise force to member 20 which transmits this force, via abutment 30, to the lower end 10 of the brake shoe web member 2. The anti-clockwise force acting on the brake shoe web member 2 would tend to force the member 2 in an anti-clockwise direction. However, as the expander means 4 also applies a clockwise force to end 5 of member 2, the overall effect is simply to cause both brake shoes 7, 8 to press hard on the brake drum and thereby cause full braking to come into effect.

It should be noted that an abutment 52 is attached to back plate 12 in order to prevent excessive forces being applied to pin 41 and the bottom of slot 40 under heavy braking.

The reversing drum brake 1 operates as follows during normal braking under reverse motion, in an anti-clockwise direction indicated by arrow 51.

As the towing vehicle reverses, the known overrun coupling (not shown) pulls on the brake cable (not shown) as before, to cause expander device 4 to apply an outward force to the top ends 5, 6 of respective brake shoe web members 2, 3. In this case, a clockwise force is applied via member 2 to the abutment 30, assisted by the friction between the brake shoe 7 and the drum which is now initially rotating in a clockwise direction.

The abutment 30 applies a clockwise force to member 20. Since pin 41 is attached to member 20, the pin 41 is urged in a clockwise direction and guided inwardly along the slot 40 in member 21, thereby causing both members 20, 21 to collapse inwardly towards the centre 45 of the brake 1. In turn, the lower ends 10, 11 of respective brake shoe web member 2, 3 follow the movement of members 20, 21 and move inwardly relative to the brake drum, thereby moving brake shoes 7, 8 away from the brake drum so that their braking effect on the drum is completely eliminated or negligible.

Thus, during reversing movement of the trailer, the drum brake is caused to collapse and braking is thereby diminished to allow the trailer to reverse. It is preferable that members 20, 21 are so arranged that during brake collapse the pin 41 travels generally along a radius of a circle centred at point 22.

The aforementioned abutment 52 may also prevent excessive forces being applied to pin 41 and to the top of slot 40 when in the collapsed state due to a top edge of the member 20 impinging abutment 52 at point 81.

The collapsing mechanism 9 may be arranged so the degree of the movement during collapsing is limited so that there is sufficient movement left in the expander device 4 to allow the brakes still to be applied by means of a handbrake (not shown) when required, the handbrake having a greater travel than the overrun coupling.

The spring 35 automatically causes the members 20, 21, and pin 41 to assume their original positions (shown in Figure 1) when the brake cable of the overrun coupling is relaxed.

As an alternative to the above mentioned embodiment, the collapsing mechanism may be arranged so that only one of the brake shoe web members is caused to collapse.

It is preferable to make the cranked member 20, 21 of parallel pieces of steel. Alternatively, the members may be modified so that each comprises a single piece of steel. The members 20, 21 may be of any suitable shape, for example, substantially straight, depending on the particular situation in which the collapsing mechanism is used.

Any suitable type of guide means may be provided as an alternative to the pin 41 and slot 40.

It has been found that the collapsing mechanism 9 requires a relatively small "roll off" force by the towing vehicle to enable the brake shoes to collapse inwardly when the trailer is reversing.

The expander device 4 may be of any suitable type.

It is preferred to provide an expander device 4 as seen in the Figures. In a preferred embodiment the expander device 4 is a self-adjusting device - that is, the expander device is automatically adjusted as the brake shoes become worn.

The self-adjusting expander device 4 includes a main housing 60 (Figures 4 and 5) having a pin 61 fixed therein. An irregularly-shaped lever arrangement 62 is pivotally mounted on the pin 61.

A brake cable (not shown) from a coupling overrun device is looped around the lever 62 at a position 63 and is thereby operable to cause the lever 62 to pivot about the pin 61. At a position generally opposite point 63, that is at position 64, the lever 62 is arranged to abut, via an abutment surface 59, the top end 6 of the brake member 3.

The top end 5 of the brake shoe web member 2 is engaged in a slotted head 168 of an adjuster screw 68. A screw-threaded shaft 90 of the screw 68 is received in a threaded bore 91 in an adjuster member 69. The adjuster member 69 includes a shaft 92 which is rotatable within an annular collar 93 of the housing 60. The adjuster member 69 includes a toothed ring 94.

The housing 60 includes a segment-shaped slot 95 approximately midway along the extent of the housing. The slot 95 is arranged to co-operate with a pin 66 of a pivotal member 96.

The pin 66 includes a substantially planar rectangular portion 97 which projects perpendicularly from a main portion 98 of the member 96, and an end retainer portion 99 which projects perpendicularly, in a downwards direction, from the rectangular portion 97.

The main portion 98 of the pivotal member 96 is substantially planar and includes an aperture 73 in which end 101 of the fixed link 74 is fixed. End 110 of the fixed link 74 is fixed to web member 3. One end 104 of a cable 79 is fixed at position 82 so as to project substantially perpendicularly away from the main plane of the main portion 98. The cable 79 is slidably received in a steel tube 80 which is attached to the backplate 12 and which extends from a position adjacent the expander device 4 to a position adjacent the collapsing mechanism 9 (see Figure 1). End 78 of the cable 79 is attached to the cranked member 20 or the pin 41.

A cranked arm 105 extends from the main portion 98 and includes an indexing finger 70. The indexing finger 70 is arranged to co-operate with the toothed-ring 94 of the adjuster member 69 so as to screw the adjuster screw 68 outwardly and thereby adjust the position of the brake shoes 2, 3.

The self-adjusting expander device 4 operates as follows: During normal braking in the forward direction, a coupling (not shown) pulls on the brake cable (not shown) which is looped around lever 62 at position 63. This causes lever 62, to pivot about pin 61 so that the part of the lever disposed at position 64 is urged outwardly against brake shoe web member 3. Thus, in effect, the length of the expander device 4 between the brake shoe web members 2, 3 increases and, consequently, the brake shoes 7, 8 are urged outwardly against the brake drum, to effect braking of the vehicle.

During this normal braking process, the web member 3 (to which fixed link 74 is attached) moves outwardly. This causes the fixed link 74 to move leftwardly slightly (as seen in Figure 1) and, as a result, the pivotal member 96 is caused to pivot within slot 95 in a clockwise direction. If a predetermined amount of brake shoe wear has occurred due to the previous braking operations, then a tip of the indexing finger 70 will ride up over the next tooth on the toothed ring 94 of the adjuster member 69.

When the brake cable (not shown) is relaxed so as to release the brakes, lever 62 assumes its original position and pivotal member 96 pivots back in an anti-clockwise direction to its original position. As the pivotal member 96 reverts to its original position, the indexing finger 70 causes the toothed ring 94 to index and thereby cause screw 68 to move outwardly slightly. Thus, the brake shoe web members 2, 3 and also the brake shoes 7,8 move closer to the brake drum so that the brakes are adjusted.

It should be noted that, if the brake shoes 7, 8 have not been worn by the predetermined amount, then the tip of the indexing finger 70 will not ride up over the next tooth on the toothed ring 94 and screw 68 will not be caused to move outwardly slightly; that is no adjustment will take place.

When the towing vehicle is reversing, the coupling (not shown) pulls upon the brake cable (not shown) thereby causing the lever 62 to pivot as described previously.

However, as discussed above, during reversing, the brake is caused to collapse due to cranked members 20, 21 and brake shoe web members 2, 3 moving inwardly towards the centre of the brake.

Since end 78 of the cable 79 is fixed to the curved member 20 or the pin 41, the end 78 of the cable is also pulled inwardly during the collapse of the brake. As a consequence, end 104 of the cable 79 applies a force to the pivotal member 96 thereby causing planar rectangular portion 97 of pin 66 to slide outwardly slightly. As a result, the pivotal member 96 moves outwardly slightly so that the tip of the indexing finger 70 is disengaged from the toothed ring 94 of the adjuster member 69. Thus, although the pivotal member 96 is caused to pivot when the towing vehicle is reversing (as it does when the towing vehicle is travelling in the forward direction), the indexing finger 70 does not contact toothed ring 94 and, therefore, no adjustment takes place.

When the brake cable (not shown) is relaxed so as to release the brakes, lever 62 and pivotal member 96 pivot back to their original positions and spring 35 automatically causes the members 20, 21 and pin 41 to assume their original positions. Furthermore, the cable 79 assumes its original position and, accordingly, indexing finger 70 re-engages the toothed ring 69.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims (31)

1. A reversing drum brake including a collapsing mechanism, the mechanism comprising a first control member operatively connected to a brake shoe, guide means being provided for guiding travel of said control member so as to control travel of said brake shoe between a first position and a second position spaced inwardly from said first position, the arrangement being such that when a force is applied in a first direction to said control member travel of said control member is guided by said guide means and said brake shoe moves towards said second position.

2. A reversing drum brake according to Claim 1, wherein said guide means is arranged to provide guided sliding movement.

3. A reversing drum brake according to Claim 1 or Claim 2, including first and second control members operatively connected to a pair of brake shoes.

4. A reversing drum brake according to Claim 3, wherein said guide means is arranged to guide the travel of one of said control members relative to the other so as to control travel of at least one of said brake shoes between said first position and said second position.

5. A reversing drum brake according to Claim 3 or Claim 4, wherein the control members are operatively connected adjacent to respective opposing ends of said pair of brake shoes.

6. A reversing drum brake according to any of Claims 3 to 5, wherein a first element of said guide means is provided by said first control member and a second element of said guide means is arranged to co-operate with said first element and is provided by said second control member.

7. A reversing drum brake according to any of Claims 3 to 6, wherein said guide means comprises a guide track defined by said first control member and a guide member provided on said second control member arranged to cooperate with said guide track.

8. A reversing drum brake according to Claim 7, wherein said guide track comprises a slot in said first control member.

9. A reversing drum brake according to Claim 7 or Claim 8, wherein said guide member comprises a projecting member.

10. A device according to any of the preceding claims, wherein the or each of said control members includes an abutment means arranged to co-operate with a respective brake shoe or a part connected thereto to operatively connect the respective said control member(s) to the respective brake shoe(s).

11. A reversing drum brake according to any preceding claim, wherein said first control member is mounted for pivotal movement about a first fixed pivot point.

12. A reversing drum brake according to any of Claims 3 to 9, wherein said second control member is mounted for pivotal movement about a second fixed pivot point.

13. A reversing drum brake according to Claim 11 and Claim 12, wherein said first and second fixed pivot points are disposed diametrically opposite to one another.

14. A reversing drum brake according to any preceding claim, wherein said first control member is generally curved in shape.

15. A device according to any of Claims 3 to 9, wherein said second control member is generally curved in shape.

16. A collapsing mechanism according to any of Claims 1 to 15 for a reversing drum brake per se.

17. A reversing drum brake including a self-adjusting device, the self-adjusting device comprising a first member and a second member operatively connected between opposing ends of a pair of brake shoes of the brake, adjuster means being provided for adjusting the distance between said first and second members, wherein said adjuster means is operable to increase automatically said distance when the distance between at least one of said brake shoes and a brake drum is greater than a predetermined distance.

18. A reversing drum brake according to Claim 17, wherein said adjuster means is arranged to operate to increase automatically said distance when a vehicle which includes said reversing drum brake is travelling in the forward direction.

19. A reversing drum brake according to Claim 17 or Claim 18, wherein said adjuster means is arranged to cause a part of said first member to be screwed outwardly in order to increase the distance between said first and second members.

20. A reversing drum brake according to any of Claims 17 to 19, including a rotatable indexing member.

21. A reversing drum brake according to Claim 20, wherein the self-adjusting device is arranged such that rotation of said indexing member causes said first member to be screwed outwardly in order to increase the distance between said first and second members.

22. A reversing drum brake according to Claim 20 or Claim 21, including indexing member actuator means arranged to cause said indexing member to rotate.

23. A reversing drum brake according to Claim 22, wherein said indexing member actuator means is arranged to pivot between first and second positions in order to cause rotation of said indexing member.

24. A reversing drum brake according to any of Claims 17 to 23, wherein said self-adjusting device is arranged such that movement of said indexing member between said first and second positions is only caused when the distance between said at least one brake shoe and said brake drum is greater than said predetermined distance.

25. A reversing drum brake according to any of Claims 17 to 24, wherein said second member comprises a lever means.

26. A reversing drum brake according to any of Claims 17 to 25, wherein means is provided for rendering the adjuster means inoperative when a vehicle which includes said reversing drum brake is travelling in a reverse direction.

27. A reversing drum brake according to any of Claims 17 to 26, wherein a link means is provided between said adjuster means and a part of a collapsing mechanism of the reversing drum brake.

28. A reversing drum brake according to Claim 27 when dependent upon Claim 22 or Claim 23, wherein said link means is arranged to retract said indexing member actuator means from a position in which it is able to effect rotation of said indexing member to a position in which it is unable to effect rotation of said indexing member.

29. A self-adjusting device according to any of Claims 17 to 28 for a reversing drum brake per se.

30. A reversing drum brake according to any of the preceding claims.

31. A reversing drum brake substantially as hereinbefore described with reference to the accompanying diagrammatic drawings.