CA1169366A - Push rod slack adjuster - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A slack adjuster for axially moved push rods is provided.
An axially extending rotating actuating shaft turns a helical, driving cam member that in turn axially displaces a non-rotating driven cam member. The driving and driven helical cam members are located in a housing with the actuating shaft extending out of one end thereof and a threaded push rod extending out of the other end of the housing. A helical return spring is positioned between the driven cam and the inner wall of the housing to bias the cam members together. The push rod is held against rotation intern-ally of the housing by a flange whose periphery is frictionally engaged by the return spring. A nut is threaded onto the rod and engaged by the driven cam member to transmit axial force to the push rod; and relative extension of the push rod from the cam members is accomplished by a one way spring brake acting on the nut and a disc clutch drive between the driving cam and nut. Lost motion is provided to prevent rotation of the nut on the rod during normal push rod clearance, and rotation of the nut on the push rod occurs when excessive push rod clearance occurs.

Description

3~i This is a division of Canadian Application Serial No.
346,262, filed February 22, 1980.
The present invention relates to a new and improved caliper brake having a new and improved automatic adjusting mechanism wherein the brake clearance can be precisely increased or decreased manually from a point exterior of the brake while the brake is in operative position on the vehicle on which it is installed.
A nun~er of designs o~ rotary cam actuators for caliper brakes have been provided by the prior art and which suffer from a number of adjustment and maintenance difficulties. In the type of actuator with which we are concerned, the brake lining is squeezed against the rotating disc by a threaded post that in turn is engaged by a threaded nut that in turn is axially driven by a rotary cam mechanism. In some of these mechanisms, the rotary drive structure for the cam is in sliding contact with portions o~ the nut, and when corrosion occurs o.r dirt enters the structure, the nut may bind to the rotary drive struc-ture so that it may drive the nut in both dlrections over the threaded post thereby preventing proper clea.rance adjustment.
In other types of these stru~tures, the connection be-tween the nut and the rotary drive structure is such that the post is held stationary while the nut is adjusted both manually and automatically to control brake clearance. In some of these the nut cannot be backed off manually to increase clearance in the brake without removing it~from the vehicle in which it is installed.
In some other types of these brake mechanisms, it is possible to retract the post to such an extent that the nut be-comes jammed onto the threads of the post with such severity that the automatic adjusting portion of the brake slips without ~ :

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making an automatic adjustment o~ the brake. Where such struc-tures are actuated by air pressure, or other mechanism wherein the actuating lever movement is not proportional to the brake applying movement, the lack of adjustment is not sensed by the driver, and unequal brake applications can occur.
In still other types of these structures, haxd to seal passages lead through the housing to the adjustment mechanism and/or the threaded nut extends externally of the housing where corrosion can freeze the nut if rubber diaphragm type covers become damaged or do not sea] for any reason.
According to the present in~ention there is provided a self-adjusting brake mechanism, the mechanism comprising trans-latable rod means for effect:ng frictional engagement between friction element means provicled thereon and a rotor element of the brake mechanism, the rod means having a first position rela-tive to the rotor elementi rotary actuating means for causing translation of the rod means from the first position in a brake applying direction; and rod eldjustment means for indexing the rod means in the brake applying direction to maintain a clear-ance within predetermined lim1ts between the friction element means and the rotor element, the rod adjustment means including a rotatable annular nut circumscribing and threadably engaging the rod means whereby rotation of the annular nut indexes the rod means in the brake applying direction; clutch means for transmitting rotary motion from the rotary actuating means to the annular nut; and lost mot:ion means cooperating with the clutch means whereby the rod means are indexed in the brake applying direction after a predetermined rotation of ~he rotary actuating means.

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In the preferred automatic adjuster disclosed herein the adjuster cannot be manual:Ly adjusted to a point making the automatic adjusting mechanism become inoperative.
Further features and advantages will be apparent to those skilled in the art to which the invention relatesO
In the drawings, Figure 1 is a longitudinal cross-sectional view through ~ :
a rotary cam actuated disc brake incorporating principles of the present invention.

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Figure 2 is an exploded view of portions of the auto-matic adjusting mechanism shown in Figure 1.
Figure 3 is an elevational view of the embodiment shown in Figures 1 and 2 and showing an air pressure actuator for the brake.
Figure 4 is a cross-sectional view taken approximately on the line 4-4 of Figure 1.
Figure 5 is a fragmentary cross-sectional view taken approximately along the line 5-5 of Figure 1, and showing a lost motion connection in the automatic adjusting mechanism.
Figure 6 is a fragmentary enlarged view of another em-bodiment of lost motion connection.

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Figure 7 is a fragmentary lon~itudinal sectional view similar to Figure 1 r but showing another embodiment of brake structure.
Figure 8 is a fragmentary enlarged sectional view taken approximately on the line ~-8 of ~igure 7.
The reference numeral 11 indicates generally a cam actuated disc brake constructed in accordance with a first em-bodiment of the invention. The brake 11 includes a caliper housing 12 that is supported adjacent a rotor 13. The caliper 12 is supported so that it may slide in an axial direction rela-tive to the associated rotor 13 but is held against rotation relative to the rotor.
As is typical with sliding caliper type disc brakes, the caliper 12 has a first leg 14 disposed adjacent to one of the braking surfaces of the rotor 13 and to which a brake pad 15 is affixed in any suitable manner. A second leg 16 of the caliper 12 is disposed adjacent the opposite ro-tox braking sur-face. An actuating mechanism, indicated generally by the re-ference numeral 17 and an automatic adjusting mechanism, indi-cated generally by the reference numeral 18, are associated with the caliper leg 16.These mechanisms act upon a brake pad 19 that is disposed in opposition to the brake pad 15 and which cooper-ates with the adjacent braking surface of the rotor 13.
The caliper leg 16 is formed with an elongated bore 21 in which a non-rotatable cam element 22 and a rotary cam element 23 are supported. The non-rotatable cam element 22 has a heli-cal cam surface 29 formed on its rearward most face (Figure 2).
The cam element 22 is supported within the bore ~1 for axial movement but is held against rotativn. This is accomplished by means of a staking pin 25-(Figures 2 and 4) that is held in place at the base of a tapped opening 26 of the caliper leg 16.
The pin 25 has a key portion 27 that extends into an elongated groove 28 formed in the cam member 22.
The cam element 23 also has a helical cam surface 29 (Figure 2) that is complementary in shape to the cam surface 24 and which is juxtaposed to it. A suitable antifriction bearing 31 is interposed between the cam surfaces 29 and 24 so as to limit the amount of friction between these surfaces.
The face 32 of the cam element 23 opposite its cam sur-face 29 is engaged with an antifriction bearing 33 which, inturn, bears against a closure plug 34 that is affixed across the open end of the bore 21 by means of machine screws 35.
The closure plug 34 is formed with an axially extending bore 36 in which a sleeve bearing 37 and seal 38 are supported.
An actuating shaft 39 extends through the bore 36 and is rotat-ably supported by the bearing 37. An actuating lever 41 is non-rotatably affixed to the act~lating shaft 39 by a s~line and machine screw 42. The actuating lever 41 is pivotably connected to a rod 43 of an actuating air motor 44 (Figure 3) that is fixed by means of a bracket 45 relative to the caliper assembly 12.
The actuating motor 44 effects rotation of the actuating shaft 39 via the lever 41, as will hecome apparent.
The actuating shaft 39 has a generally hollow cylin-drical section 46 that extends into the bore 21 and which ex-tends radially inwardly of the cam element 23. A spline connec-tion 47 rotatably connects the actuator shaft portion 46 with the cam element 23 to effect simultaneous rotation of these compo-nents.
; The automatic adjustlng mechanism 18 includes an annu-lar nut 48 having a shoulder 49 for abutment with a corresponding 936~

shoulder 51 fonmed on the cam element 22. Internal threads 52 of the nut 48 are engaged with threads of a longitudinall~ ex-tending male threaded member or rod 53. The male threaded mem-ber 53 has a reduced diameter end carrying a collar 54 that is engaged with a load distributor 55 which bears against the brake pad 19. A suitable boot or dust seal 56 encircles the collar 54 and is held in place relative to the open end of the caliper bore 21 by means of a retaining ring 57 that is position-ed against the inner end of the bore 21 to seal the internal portions of the brake actuating mechanism 17 and automatic ad-justing mechanism 18. A helically wound compression spring 58 is positioned between the seal retaining ring 57 and a hat shaped combination bearing plate and dirt seal or washer 59, the radially outer portlon of which bears against the cam 22 to effect brake retraction, as will become apparent. The spring 58 can also be termed a return spring.
The nut 48 has an axially extending projection 60 that is slotted, as at 61, to receive one or more tangs 62 of a clutch plate 63~ There lS a predetermined clearance of approximately five degrees of rotation between the tangs 62 and sides of the -slots 61 which clearance establishes the normal running clearance of the brake 11, as will become apparent.
The clutch plate 63 is received between a pair of clutch plates 64 and 65 which, in turn, have a tanged connection to the hollow cylindrical section 46 of the actuating shaft por-~ tion 39. The tanged connection comprises tangs 66 formed on the : clutch plates 64 and 65 (Figure 5) and slots 67 formed in the ; hollow cylindrical section 46. A snap ring 68 bears against the clutch plate 64 and is affixed wlthin a groove in the hollow cylindrical section 46. A large compression spring 69 bears 3~;~

against the clutch plate 65 and a shoulder 71 fonmed at the base of the hollow cylindrical section 46. The spring 69 presets the pressure existing between the clutch plates 64 and 65 and the clutch plate 63 and determines the torque at which this clutch will slip, as will become apparent.
It will be seen that forward rotation of the actuating shaft 39 will produce an advancing rotation of the nut 48 through the clutch plate 63, except during the five degrees of lost motion clearance between the tangs 62 and the sides of the slots 61 in the nut. In order that this five degrees of lost motion will occur at the start of each actuation, means are pro-vided for preventing the nut from being rotated backwardly when the actuating shaft 39 is rotated backwardly. In the embodiment shown in Figures 1-5, this is accomplished by a spring brake 72 that encircles the nut 48 and which has a projection 73 fixed relative to the nonrot~ting cam element 22. The spring brake 72 acts as a one way brake so that the nut 4~ may be rotated in the for~ard direction, but not in the reverse direction. During ini-tial reverse rotation, the reactive forces produced by the brake lining of the rotor 13 hold the shoulder 49 of the nut in engage-ment with the shoulder 51 of the actuating cam element 22 to prevent rotation of the nut. Thereafter, the nut ~8 moves out of engagement with the shoulder 51 and rotation of the nut 48 is prevented by the spring brake. During this time, the shoulder 49 of the nut moves away from the shoulder Sl while the forward face of the nut 4g moves into engagement with the washer 59 which thereafter positively retracts the nut and push rod 53 to leave running clearance in the brake. In the embodiments shown in Figures 1-5, there is a clearance of 0O015 inch between the shoulders 49 and 51 at this time. Throughout this deactuating ~ 3~6 movement of the shaft 39, the clutch discs 64 and 65 axe rotated clockwise as seen in Figure 5 to move the tang ~2 of the clutch disc 63 into engagement with the trailing side edges o~ the slot 61. During the next actuation, therefore, the tangs 62 will move the full five degrees of counter clockwise rotation as seen in Figure 5 before they engage the leading side edges of the slot 61. The clearance between the shoulders 49 and 51 previous-ly referred to prevents binding between the nut and the cam por-tion 22 during automatic adjustment.
One of the problems which occur with prior art slack adjuster constructions is that they do not allow access to the threaded rod 53 after the brake is installed. In the construc-tion so far described, the nonrotating cam member 22 is posi-tioned adjacent the nut 48~ and the rotating portion 23 of the cam is positioned outwardly of the nonrotating portion 22 of the cam. With this construction, the xotating portion 23 can be driven by an axially extending shaft projecting through the outer wall of the actuator away from the brake rotor and the actuating and adjusting mechanism is positioned between the closure plug 34 and the inner seal structure of the brake. This seal struc-ture includes the hat shaped washer 59. It is a feature of the present invention that the outer periphery of the washer 59 is always held into sliding engagement with the nonrotating cam element 22 while the center portion of the washer 59 has a sliding nonrotational close fit with the actuating rod 53. It will now be seen that the washer 59, therefore, provides a metal sliding seal which protects the inner workings of the brake while also providing a ~riction clutch for preventing rotation of the push rod 53 by the nut 48. In some prior art designs, it is necessary to non-rotatably hold ~he push rod 53 by sliding struc-_ 9 ~1~i93~

ture located in the space adjacent the rotor 13 where the slid-ing structure is bathed in water and dirt.
According to a further feature Of the present inven-tion r the running clearance of the brake can be adjusted while the brake is in position over the rotor by rotating the push rod 53 relative to the nut 48. This is accomplished by a torque transmitting surface 74, which in the present instance is a screwdriver slot, fixed in the end of the actuating rod 53.
Access to the screwdriver slot 54 is had through a passageway 75 that extends through the center of the actuating shaft 39 and the outer end of which is closed off by machine screw 42.
In some instances it is possible for a mechanic to un-knowingly back off the actuating rod 53 to such an extent that it is jammed up against the actuating shaft 39. When this is done, the bind between the actuating rod 53 and the shaft will be such that the clutch plates 63, 64 and 65 slip without adjusting the nut 48. This, of course, will defeat the self adjusting fea-ture of the brake.

In the embodiment shown in Figures 1-5, this is pre-vented by providing teeth on the abutting surfaces of the rod and the surface which it abuts whi h prevent the rod from being ro-tated into a jammed condition. In the embodiment shown, it is accomplished by providing an annular ring 76 which surrounds the passageway 75 and which has ridges or square teeth 77 on its abutment surface. The end of the rod 53~has an abutment 78 pressed therein for engaging the square teeth, and its abutment surface is provided with ratchet teeth 79~, the flat sides of which will engage the flat side of the square teeth 77 to limit the retraction of the rod 53 toward the annular ring 76. The ratchet teeth 79, however, permit the rod 53 to be easily xotated 3~,~

in an advancing direction away ~rom the annular ring 76 by the automatic adjusting mechanism.
Relining of the brakes is made simple by the present invention. The machine screw 42 is removed from the passageway 75, and a screwdriver is inserted into the slot 74 to turn the rod 53 counterclockwise as seen in Figures 4 and 5. This backs the adjustment rod 53 out of the nut 48 to provide clearance between the pads 15 and 19 and the rotor 13. New pads 15 and 19 are inserted, the brake assembly is put back on the vehicle and the adjustment rod 53 is rotated clockwise until the brake pads are brought adjacent the rotor 13. During rotation of the ad-justment rod 53 by the screwdriver, its motion is opposed by sliding friction between the washer 59 and the cla~lping action of spring 58 on the non-rotatable cam member 22. This friction-al engagement will hold the adjustment rod 53 in its adjusted position, and the clutch plates 63, 64 and 65 are operative thereafter to rotate the nut 4B relative to the adjuster rod 53.
The machine screw 42 is reinstalled to seal off the mechanism from water and dirt.
The figures illustrate the brake 11 in a released posi-tion. To actuate the brake, the piston rod 43 is extended so as to rotate the lever 41 and shaft 39 in a counterclockwise direc tion as seen in Figures 3-5. This effects rotation of the cam element 23 relative to the cam element 22 to exert an axial force on the cam element 22. The cam element 22 i9, therefore, shift-ed to the left along with the nut 48 and threaded member 53 to compress the spring 58. The brake pad l9 will then be brought in-to engagement with the associated braking surface of the rotor 13 and effect a reactive force on the caliper 12 to slide it toward the right as viewed in Figure 1. The brake pad 15 will, there-fore, be brought into engagement with the opposing braking sur-face of the rotor 13.
At the time the cam element 23 is rotated, the clutch plates 64 and 65 will also effect rotation of the clutch plate 63. Assuming that insufficient lining wear has taken place to require adjustment, the tangs 62 of the clutch plate 63 will merely traverse the slots 61 and no rotation of the nut 48 will result.
Assurning, however, that sufficient lining wear has taken place so as to necessitate adjustment, the clutch plate 63 will take up the clearance in the slots 61 and will rotate the nut 48 in an adjusting dlrection. This rotation is permitted by slippage of the one way spring brake 72. The rotation o~ the nut 48 will cause extension of the screw threaded member 53 to take up the clearance, the latter element being held against rotation by the washer 59 and compression spring 58. Once the brake pads 15 and 19 engage the rotor braking surface with a predetermined pressure, as set by the spring 69, continued rotation of the cam 23 in the actuating direction will cause the clutch plates 64 and 65 to slip relative to the clutch plate 63. Therefore, over adjustment is prevented.
Assuming that adjustment has been made in the manner -~ aforedescribed, ~the brake is released by rotating the cam element 23 in the opposlte direction. Thus, the cam suraces 29 and 24 permit the spring 58~to~return the cam element 22 to its at rest position along with the nut 48 and threaded member 53. Any~ten-dency for the nut 48 to rotate in an anti-adjusting direction will, however, be prevented by the one-way spring brake 72. Thus, the nut 48 will~be maintained in its newly adjusted position re-30 lative to the threaded mernber 53. ~-'~

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The embodiment shown in Figure 6 corresponds generally to the embodiment shown in Figures 1 through 5, except in the arrangement of lost motion connection utilized. Those portions of the embodiment shown in Figure 6 which correspond to similar portions of the embodiment shown in Figures 1-5 are designated by a like reference numeral characterized further in that a suffix "a" is affixed thereto.
Figure 6 shows a type of lost motion connection which can be used to replace the clearance between the tangs 62 and slots 61. In the embodiment shown in Figure 6, the tangs 62 will substantially fill the slots 6I and the five degrees of lost motion is provided by clearance between the projection 73a of the spring brake 72a and its retaining surfaces in the non-rotatable cam element 22a.
Operation of the embodiment shown in Figure 6 will be similar to that of the device shown in Figures l through 5 ex-cept for the location where the lost motion takes place.
The embodiment shown in Figures 7 and 8 corresponds generally to the embodiments previously described, but differs principally in that the clamping spring for the clutch is posi-tioned on the inner side of the clutch plates instead of the outer side as occurred in the embodiments previously described.
Those portions of the embodiments shown in Figures 7 and 8 which are similar to corresponding portions of the embodiments shown in Figures 1-6 are designated by a like reference numeral charac-terized further in that a suffix "b" is affixed thereto.
In the embodiment shown in Figures 7 and 8, the nut 48b is elongated and the clutch spring 69b is positioned between the inner clutch plate 64b, and an annular spring retainer 81 that in turn is positioned against an outwardly facing shoulder 1~936~

82 in the nut 48b. In order that the spring 69b will be posi-tioned between two surfaces which do not rotate relative to each other, the clutch plates 64b and 65b are slidably coupled to the nut 48b rather than to the actuating shaft 39b. The in-ner periphery of the clutch plates 64b and 65b carry tangs 66b that are received in the slot 61b of the nut 48b, while the clutch plate 63b is supplied with tangs 82 on its outer peri-phery that are received in slots 83 in the inner periphery of the rotary cam member 23b. The actuating shaft member 39b also carries teeth that engage the splined configuration 47b of the cam member 23b. This construction has the advantage that it permits the actuating shaft 39b to have a much shorter annular driving projection 46b than was required in the previously des-cribed embodiments.
The clutch discs 64b and 65b are held onto the nut 48b by a snap ring 84 that is positioned outwardly of the clutch plate 65b, and which is received in a groove 85 in the outer end of the nut 48b. Also in the embodiment shown in Figures 7 and 8, no collar 54 is used, and the rod 53b has its inner end enlarged to act as the retainer for the dust seal 56b. Also, the sleeve bearing 37 of the previous embodiment is replaced by two roller bearings 86 which, as in the previous embodlment, support and center not only the drive shaft 39b, but holdthe cam~member 23b out of sliding engagement with the side walls of the bore Zlb by reason of the tightly fitting spline 47b. Five degrees of lost motion are provided between the tangs 32 of the clutch plate 63b and the sidewalls of the grooves 83.
In all of the embodiments above described, the side wall of the elongated bore 21 is enlarged slightly as at 87 over the rotary portion of the cam actuator, so that it is held out of - 14 ~

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sliding engagement with the housing by the actuating shaft 39.
The spline 47 between the rotary cam 23, and the annular shaft extension 46 is a tight sliding fit so that the rotary cam 23 is held away from the side walls of the bore 87. On the other hand, the axially driven cam 22 bears against the side walls of the bore 21, and it in turn journals the nut ~8 to center the threaded rod 53 relative to the actuating structure. It will further be seen that the construction of the invention seals off the frictional drive mechanisms between the sliding washer 59 and the rotary seal 38 which surrounds the shaft 39, so that the torque developed by the frictional devices does not appreciably change during use. It will further be seen that the device can nevertheless be manually adjusted while the actuator is install-ed on the vehicle through a passageway through the actuating shaft which is located in the outer end of the housing.
While the invention has been described in considerable detail, the applicant does not wish to be limited to the parti-cular embodiments shown and described, and it is intended to cover hereby all novel adaptations, modifications, and arrange-ments thereof, which come within the practice of those skilled inthe art to which the invention relates, and which come within the scope of the following claims.

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Claims (56)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A self-adjusting brake mechanism, said mechanism comprising:
translatable rod means for effecting frictional engage-ment between friction element means provided thereon and a rotor element of said brake mechanism, said rod means having a first position relative to said rotor element;
rotary actuating means for causing translation of said rod means from said first position in a brake applying direction;
and rod adjustment means for indexing said rod means in said brake applying direction. to maintain a clearance within pre-determined limits between said friction element means and said rotor element, said rod adjustment means including;
(a) a rotatable annular nut circumscribing and thread-ably engaging said rod means whereby rotation of said annular nut indexes said rod means in said brake applying direction;
(b) clutch means for transmitting rotary motion from said rotary actuating means to said annular nut; and (c) lost motion means cooperating with said clutch means whereby said rod means are indexed in said brake applying direction after a predetermined rotation of said rotary actuat-ing means.

2. The brake mechanism of claim 1 wherein said clutch means comprise an annular inner clutch plate frictionally en-gaged on each side thereof by an annular outer clutch plate, said inner and outer clutch plates radially extending between said annular nut and said rotary actuating means, and means for maintaining said outer clutch plates in frictional engagement with said inner clutch plate.

3. The brake mechanism of claim 2 wherein said lost motion means comprise at least one external tang projecting radially outwardly from each of said outer clutch plates for en-gaging said rotary actuating means and at least one internal tang projecting radially inward from said inner clutch plate for engaging said annular nut, whereby said annular nut is rotated with respect to said rod means only after a predetermined rota-tion of said rotary actuating means.

4. The brake mechanism of claim 3 wherein said at least one internal tang engages an axial slot in said annular nut, the circumferential width of said axial slot in said annul-ar nut being greater than the circumferential width of said in-ternal tang to permit a predetermined amount of lost motion whereby said clutch means transmit said rotary motion to said annular nut only after a predetermined rotation of said rotary actuating means.

5. The brake mechanism of claim 4 wherein said pre-determined amount of lost motion is 5° of rotation commencing with the start of each actuation of said brake mechanism.

6. The brake mechanism of claim 4 further including restraining means for preventing reverse rotation of said annular nut upon deactuation and counter-rotation of said brake mechanism.

7. The brake mechanism of claim 6 wherein said re-straining means comprise a spring member encircling at least a portion of said annular nut for permitting rotation of said annular nut in a direction to induce indexing of said rod means in said brake applying direction only.

8. The brake mechanism of claim 7 wherein said rotary actuating means comprise; a rotatable cam member having a heli-cal cam surface formed at one end thereof, a rotatable actuating member coaxially disposed within and connected with said rotat-able cam member for imparting rotational motion to said rotatable cam member and a non-rotatable cam member cooperatively engaged with said rotatable cam member for axial displacement thereof in said brake applying direction upon rotation of said rotation-al cam member by said actuating member.

9. The brake mechanism of claim 8 wherein said non-rotatable cam member includes at the end thereof adjacent said one end of said rotatable cam member a complementary helical cam surface.

10. The brake mechanism of claim 9 wherein said ro-tatable and non-rotatable cam members encircle at least a portion of said translatable rod means and said annular nut threadably engaged thereto, said annular nut having a shank portion and a radially projecting shoulder portion.

11. The brake mechanism of claim 10 wherein said non-rotatable cam member includes a radially inwardly projecting shoulder portion for engaging said shoulder portion on said annular nut for urging the combination of said annular nut and said rod means in said brake applying direction in response to rotation of said actuating member and said rotatable cam member, thereby urging said friction element means into engagement with said rotor element, said brake mechanism further including means for biasing the combination of said annular nut and said rod means in a brake releasing direction upon counter-rotation of said actuating member.

12. The brake mechanism of claim 11 wherein said axial slot formed in said annular nut is formed in said shank portion thereof and said tang projecting outwardly from each of said outer clutch plates engage an axial slot in said rotatable actu-ating member.

13. The brake mechanism of claim 12 wherein said rotor element includes a pair of oppositely facing friction surfaces, said friction element being juxtaposed with one of said friction surfaces, said other surface having second friction element means juxtaposed thereto, said mechanism fur-ther comprising a caliper having a pair of legs, one of which supports said second friction element means and the other of which includes a bore extending axially therethrough, said ro-tatable and non-rotatable cam members being concentrically dis-posed within said bore in axial alignment with one another.

14. The brake mechanism of claim 13 wherein the end of said bore distal from said rotor element is sealed by a plug member having a second axially extending bore of smaller dia-meter formed therethrough, said second bore communicating with said bore in said caliper leg, said actuating member being cylindrical in shape and including a shaft portion extending rearwardly away from said rotor element, said shaft portion being axially supported for rotation within said second bore and being adapted for connection to brake actuating means for rotating said shaft portion.

15. The brake mechanism of claim 14 further including manual adjusting means for manually adjusting said rod means with respect to said annular nut in a direction towards or away from said rotor element, said. means comprising a hollow axial passageway formed through said shaft portion for communication with the inside of said cylindrical actuating member, a ring member positioned about the opening of said passageway into said actuating member and having teeth disposed about an inner sur-face thereof and an abutment member fixed to the end of said rod means opposite the end thereof having said friction element means provided thereon, said abutment means having one way ratchet teeth and a torque receiving surface thereon, such that a torque transmitting tool may be inserted through said axial passageway to engage said torque receiving surface for rotating said rod means to selectively advance or retract said rod means relative to said annular nut, said one way ratchet teeth being disposed to contact said teeth on said annular ring to prevent excessive retraction of said rod means away from said rotor member.

16. The brake mechanism of claim 15 further including a washer non-rotatably fixed to said rod means with its outer portion wedged between said biasing means and said non-rotatable cam member, said washer and biasing means being constructed and arranged to create a restraining torque on said rod means.

17. The brake mechanism of claim 16 wherein said bias-ing means include a helically wound spring disposed between said washer and the end of said bore proximal said rotor member.

18. The brake mechanism of claim 17 further including sealing means disposed between said rod means and the periphery of said bore adjacent said biasing means to prevent the ingress of extraneous matter into said brake mechanism.

19. The brake mechanism of claims 16, 17 or 18 further including a removable plug to seal the outer end of said passage-way.

20. The brake mechanism of claim 2 wherein said lost motion means comprise at least one internal tang projecting radially inward from each of said outer clutch plates for en-gaging said annular nut and at least one external tang project-ing radially outward from said inner clutch plate for engaging said rotary actuating means, whereby said annular nut is ro-tated with respect to said rod means after a predetermined rotation of said rotary actuating means.

21. The brake mechanism of claim 20 wherein said rotary actuating means comprise a rotatable cam member having a helical cam surface formed at one end thereof, a rotatable actuating mem-ber coaxially disposed within and connected with said rotatable cam member for imparting rotational motion thereto and a non-rotatable cam member cooperatively engaged with said rotatable cam member for axial displacement in said brake applying direc-tion upon rotation of said rotatable cam member by said actuating member.

22. The brake mechanism of claim 21 wherein said at least one external tang engages an axial slot in said rotatable cam member, the circumferential width of said axial slot in said rotatable cam member being greater than the circumferential width of said external tang to permit a predetermined amount of lost motion whereby said clutch means transmit rotary motion to said annular nut only after a predetermined rotation of said rotatable cam member.

23. The brake mechanism of claim 22 wherein said pre-determined amount of lost motion is 5° of rotation commencing with the start of each actuation of said brake mechanism.

24. The brake mechanism of claim 22 further including restraining means for preventing reverse rotation of said annular nut upon deactuation and counter-rotation of said brake mechanism.

25. The brake mechanism of claim 24 wherein said re-straining means comprise a spring member encircling at least a portion of said annular nut for permitting rotation of said annular nut in a direction to induce indexing of said rod means in said brake applying direction only.

26. The brake mechanism of claim 25 wherein said non-rotatable cam member includes at the end thereof adjacent said one end of said rotatable cam member a complementary helical cam surface.

27. The brake mechanism of claim 26 wherein said ro-tatable and non rotatable cam members encircle at least a portion of said translatable rod means and said annular nut threadably engaged thereto, said annular nut having a shank portion and a radially projecting shoulder portion.

28. The brake mechanism of claim 27 wherein said non-rotatable cam member included a radially inwardly projecting shoulder portion for engaging said shoulder portion on said annular nut for urging the combination of said annular nut and said rod means in said brake applying direction in response to rotation of said actuating member and said rotatable cam member, thereby urging said friction element means into engagement with said rotor element said brake mechanism further including means for biasing the combination of said annular nut and said rod means in a brake-releasing direction upon counter-rotation of said actuating member.

29. The brake mechanism of claim 28 wherein each of said at least one internal tang projecting inwards from each of said outer clutch plates engage an axial slot in said shank portion of said annular nut.

30. The brake mechanism of claim 29 wherein said rotor element includes a pair of oppositely facing friction surfaces, said friction element being juxtaposed with one of said friction surfaces, said other surface having second friction element means juxtaposed thereto, said mechanism further comprising a caliper having a pair of legs, one of which supports said second friction element means and the other of which includes a bore extending axially therethrough, said rotatable and non-rotatable cam members being concentrically disposed within said bore in axial alignment with one another.

31. The brake mechanism of claim 30 wherein the end of said bore distal from said rotor element is sealed by a plug member having a second axially extending bore of smaller dia-meter formed therethrough, said second bore communicating with said bore in said caliper leg, said actuating member being cylindrical in shape and including a shaft portion extending rearwardly away from said rotor element, said shaft portion being axially supported for rotation within said second bore and being adapted for connection to brake actuating means for ro-tating said shaft portion.

32. The brake mechanism of claim 31 further including manual adjusting means for manually adjusting said rod means with respect to said annular nut in a direction towards or away from said rotor element, said means comprising a hollow axial passageway formed through said shaft portion for communication with the inside of said cylindrical actuating member, a ring member positioned about the opening of said passageway into said actuating member and having teeth disposed about an inner sur-face thereof and an abutment member fixed to the end of said rod means opposite the end thereof having said friction element means provided thereon, said abutment means having one way ratchet teeth and a torque receiving surface thereon, such that a torque transmitting tool may be inserted through said axial passageway to engage said torque receiving surface for rotating said rod means to selectively advance or retract said rod means relative to said annular nut, said one way ratchet teeth being disposed to contact said teeth on said annular ring to prevent excessive retraction of said rod means away from said rotor member.

33. The brake mechanism of claim 32 further including a washer non-rotatably fixed to said rod means with its outer portion wedged between said biasing means and said non-rotatable cam member, said washer and biasing means being constructed and arranged to create a restraining torque on said rod means.

34. The brake mechanism of claim 33 wherein said bias-ing means include a helically wound spring disposed between said washer and the end of said bore proximal said rotor member.

35. The brake mechanism of claim 34 further including sealing means disposed between said rod means and the periphery of said bore adjacent said biasing means to prevent the ingress of extraneous matter into said brake mechanism.

36. The brake mechanism of claims 33, 34 or 35 further including a removable plug to seal the outer end of said passage-way.

37. The brake mechanism of claim 2 including restrain-ing means for preventing reverse rotation of said annular nut upon deactuation and counter-rotation of said brake mechanism.

38. The brake mechanism of claim 37 wherein said re-straining means comprise a spring member encircling at least a portion of said annular nut for permitting rotation of said annular nut in a direction to induce indexing of said rod means in said brake applying direction only.

39. The brake mechanism of claim 38 wherein said rotary actuating means comprise a rotatable cam member having a helical cam surface formed at one end thereof, a rotatable actuating mem-ber coaxially disposed within and connected with said rotatable cam member for imparting rotational motion thereto and a non-rotatable cam member cooperatively engaged with said rotatable cam member for axial displacement in said brake applying direc-tion upon rotation of said rotatable cam member by said actuat-ing member.

40. The brake mechanism of claim 39 wherein said spring member constitutes a helical one-way spring brake one end of said spring brake being fixed to said non-rotatable cam member by means of a radial projection formed at said one end thereof.

41. The brake mechanism of claim 40 wherein said lost motion means comprise an axial slot in said non-rotatable cam member for engaging said projection on said one end of said spring brake, the circumferential width of said axial slot in said non-rotatable cam member being greater than the circum-ferential width of said projection to permit a predetermined amount of lost motion whereby said clutch means transmit rotary motion to said annular nut only after a predetermined rotation of said rotatable cam member.

42. The brake mechanism of claim 41 wherein said pre-determined amount of lost motion is 5° of rotation commencing with the start of each actuation of said brake mechanism.

43. The brake mechanism of claim 41 wherein each of said outer clutch plates include at least one external tang pro-jecting radially outward for engaging an axial slot in said actuating member and said inner clutch plate includes at least one internal tang for engaging an axial slot in said annular nut.

44. The brake mechanism of claim 43 wherein said non-rotatable cam member includes at the end thereof adjacent said one end of said rotatable cam member a complementary helical cam surface.

45. The brake mechanism of claim 44 wherein said rota-table and non-rotatable cam members encircle at least a portion of said translatable rod means and said annular nut threadably engaged thereto, said annular nut having a shank portion and a radially projecting shoulder portion, said helical spring brake being disposed about said shank portion.

46. The brake mechanism of claim 45 wherein said non-rotatable cam member includes a radially inwardly projecting shoulder portion for engaging said shoulder portion on said annular nut for urging the combination of said annular nut and said rod means in said brake applying direction in response to rotation of said actuating member and said rotatable cam member, thereby urging said friction element means into engagement with said rotor element, said brake mechanism further including means for biasing the combination of said annular nut and said rod means in a brake-releasing direction upon counter-rotation of said actuating member.

47. The brake mechanism of claim 46 wherein said axial slot formed in said annular nut is formed in said shank portion thereof.

48. The brake mechanism of claim 47 wherein said rotor element includes a pair of oppositely facing friction surfaces, said friction element being juxtaposed with one of said friction surfaces, said other surface having second fric-tion element means juxtaposed thereto, said mechanism further comprising a caliper having a pair of legs, one of which supports said second friction element means and the other of which includes a bore extending axially therethrough, said ro-tatable and non-rotatable cam members being concentrically dis-posed within said bore in axial alignment with one another.

49. The brake mechansim of claim 48 wherein the end of said bore distal from said rotor element is sealed by a plug member having a second axially extending bore of smaller diameter formed therethrough, said second bore communicating with said bore in said caliper leg, said actuating member being cylindri-cal in shape and including a shaft portion extending rearwardly away from said rotor element, said shaft portion being axially supported for rotation within said second bore and being adapt-ed for connection to brake actuating means for rotating said shaft portion.

50. The brake mechanism of claim 49 further including manual adjusting means for manually adjusting said rod means with respect to said annular nut in a direction towards or away from said rotor element, said means comprising a hollow axial passageway formed through said shaft portion for communication with the inside of said cylindrical actuating member, a ring member positioned about the opening of said passageway into said actuating member and having teeth disposed about an inner sur-face thereof and an abutment member fixed to the end of said rod means opposite the end thereof having said friction element means provided thereon, said abutment means having one way ratchet teeth and a torque receiving surface thereon, such that a torque transmitting tool may be inserted through said axial passageway to engage said torque receiving surface for rotating said rod means to selectively advance or retract said rod means relative to said annular nut, said one way ratchet teeth being disposed to contact said teeth on said annular ring to prevent excessive retraction of said rod means away from said rotor member.

51. The brake mechanism of claim 50 further including a washer non-rotatably fixed to said rod means with its outer portion wedged between said biasing means and said non-rotatable cam member, said washer and biasing means being constructed and arranged to create a restraining torque on said rod means.

52. The brake mechanism of claim 51 wherein said bias-ing means include a helically wound spring disposed between said washer and the end of said bore proximal said rotor member.

53. The brake mechansim of claim 52 further including sealing means disposed between said rod means and the periphery of said bore adjacent said biasing means to prevent the ingress of extraneous matter into said brake mechanism.

54. The brake mechanism of claims 51, 52 or 53 further including a removable plug to seal the outer end of said passage-way.

55. The brake mechanism of claims 10 or 27 wherein said spring member constitutes a helical one-way spring brake circum-scribing said shank portion of said annular nut, one end of said spring brake being fixed to said non-rotatable cam member by means of a radial projection formed at one end thereof which en-gages an axial slot formed in said non-rotatable cam member.

56. The brake mechanism of claims 18, 35 or 53 wherein said predetermined amount of lost motion is 5° of rotation com-mencing with the start of each actuation of said brake mechanism.