CA1137885A - 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

~L3~

The present invention relates to a new and improved caliper brake having a new and improved automatic adjusting mecha-nism 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 number of designs of 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 thetype of actuator with which we are concerned, the brake lining is squeezed against the rotating disc by a threaded post that inturn 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 of the nut, and when corrosion occurs or dirt enters the structure, the nut may bind to the rotary drive structure so that it may drive the nut in both directions over the threaded post thereby preventing proper clearance adjustment.
In other types of these structures, the connection between the nut and the rotary drive structure is such that the post is held stationary while the nut is adjusted both manually and auto-matically to control brake clearance. In some of these the nut cannot bebacked off manually to increase clearance in the brake without removing it from the vehicle in which it i9 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 wlthout making an automatic adjustment of the brake. Where such structures are actuated by air pressure, or other mechanism wherein the actua~ng ~ '.

113~885 lever movement is not proportional to the brake applying move-ment, the lack of adjustment is not sensed by the driver, and une~ual brake applications can occur.
In still other types of these structures, hard 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 be-come damaged or do not seal for any reason.
According to one aspect of the invention, a slack ad-juster for a brake mechanism comprises a housing having innerand outer ends, a longitudinally extending rod having external threads thereon mounted in the housing, a rotatable nut on the rod having threaded engagement therewith, a non-rotatable longi-tudinally moving actuating member abutting one side of the nut for advancing the nut and rod longitudinally toward the inner end, means for biasing the combination of the nut and the rod in a rearward brake-releasing direction upon movement of the ac-tuating member away from the inner end, a washer non-rotatably fixed to the rod with its outer portion wedged between the biasing means and the actuating member, adjusting means for ro-tating the nut relative to the push rod, thereby forwardly ad-vancing the push rod with respect to the nut when the actuating member is advanced, and the washer and biasing means being con-structed and arranged to create a restraining torque exceeding a predetermined driving torque produced by the adjusting means during advance of the actuating member.
According to a further aspect of the invention there is provided in a brake mechanism having an actuator with relative-ly rotatable components effective to cause brake actuation upon such relative rotation, a pair of cooperating threaded elements 1~3788S

for effecting adjustment of an at rest position of the brake, an automatic adjusting means for effecting rotation of one of the threaded elements relative to the other for adjusting the at rest position of the brake in response to brake pad wear, the automatic adjusting means comprising a clutch having an operative connection between one of the actuator components and one of the threaded elements for effecting rotation of the one threaded ele- -ment upon rotation of the one actuator component in a first di-rection, the operative connection including a lost motion connec-tion for permitting relative rotation of the one actuatory com-ponent relative to the one threaded element to establish the nor-mal running clearance in the brake mechanism, the clutch being effective to slip and permit rotation of the one actuator com-ponent relative to the one threaded element upon a predetermined loading for preventing overadjustment of the brake, and a one way brake cooperating with the one threaded element for limiting the return rotation of the one threaded element upon rotation of the one actuator component in the opposite direction, the clutch being operative to slip upon such return relative rotation of the one actuator componen-t upon the actuation of the one way brake.
According to another aspect of the invention, a caliper brake actuator comprises a housing having inner and outer legs which project radially inwardly on respective inner and outer sides of a rotor cavity, the inner leg having a transverse bore proceediny through the inner leg from its inner end to the rotor cavity, a cover pl.ate on the inner end, an actuating shaft ex-tending into the transverse bore through the cover plate and journaled by ~he cover plate, a rotary cam member in the bore, a non-rotatable cam member operatively abutting the rotary cam 1137~85 member to produce transverse movement, a brake applying post projecting out of the bore into the rotor cavity, the cam mem-bers being arranged to force the brake applying post out of the bore upon rotation of the rotary cam member, the non-rotatable cam member being slidingly supported by the sidewalls of the bore, the post being supported from the non-rotatable cam member, and the rotatable cam member being supported by the actuating shaft out of frictional engagement with the sidewalls of the bore.

In the preferred automatic adjuster disclosed herein the adjuster cannot be manually 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 relates.
In the drawings, Figure 1 is a longitudinal cross sectional view through a rotary cam actuated disc brake incorporating principles of the present invention.
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 embodimentshown 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.

1~371 38S

~ igure 7 is a fragmentary longitudinal sectional viewsimilar to Figure 1, but showing another embodiment of brake structure.
Figure 8 is a fragmentary enlarged sectional view taken approximately on the line 8-8 of Figure 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 rotor 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 withthe caliper leg 16. These mechanism 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 24 formed on its rearward most face (Figure 2).
The cam element 22 is supported within the bore 21 for axial movement but is held against rotation. This is accomplished by means of a staking pin 25 (Figures 2 and 4) that is held in ~137885 place at the l)ase 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.
1`he cam element 23 also has a helical cam surface 29 (Figure 2) that is complementary in shape to the cam surface 24 and which ls 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 actuating shaft 39 by a spline 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 become 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 adjusting mechanism 18 includes an annu-lar nut 48 having a shoulder 49 for abutment with a corresponding 113~885 shoulder 51 ~ormed on the cam element 22. Internal threads 52of the nut 48 ar~ engaged with threads of a longitudinally 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 portion 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 is 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 within a groove in the hollow cylindrical section 46. A large compression spring 69 bears 113~

against the clutch plate 65 and a shoulder 71 formed 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 nonrotating cam element 22. The spring brake 72 acts as a one way brake so that the nut 48 may be rotated in the forward 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 48 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 51 while the forward face of the nut 48 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 0.015 inch between the shoulders 49 and 51 at this time. Throughout this deactuating S

movement of the shaLt 39, the clutch discs 64 and 65 are ratated clockwlse as seen in Figure 5 to move the tang 62 of the clutch disc 63 into engagement with the trailing side edg~s of 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 rotating 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 friction 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 the push rod 53 by sliding struc-~37813S

ture located in tlle space adjacent the rotor 13 where the slid-ing structure is ~)athed in water and dirt.
~ ccordin~ to a further feature of the present inven-tion, the running clearance of the brake can be adjusted while the brake is ln 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 which 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. I'he ratchet teeth 79, however, permit the rod 53 to be easily rotated -~13~ S

in an adval~ci.n-l direction away from the annular ring 76 by the automatic adjus-ing mechanism.
I~elininc3 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 clamping 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 48 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 is, therefore, shift-ed to the left along with the nut 48 and threaded member 53 to compress the spring 58. The brake pad 19 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-1137~3~S

fore, ~e ~rought 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 wlll 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.
Assuming, 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 direction. This rotation is permitted by slippage of the one way spring brake 72. The rotation of 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 opposite direction. Thus, the cam surfaces 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-lative to the threaded member 53.

1137131~3S

rilhe em~odiment shown in Figure 6 corresponds generally to the embodiment shown ln 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 10 slots 61. In the embodiment shown in Figure 6, the tangs 62 will substantially fill the slots 61 and the five degrees of lost motion is provided by clearance between the projection 7~a 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 1 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 ~4b, and an annular spring retainer 81 that in turn is positioned against an outwardly facing shoulder .;'., ~,~
. . ~

1137~S

82 in the nut 48b. In order that the spring 69b will be posi-tioned between ~wo 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 pro]ection 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 embodiment, 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 21b by reason of the tightly fitting spline 47b. Five degrees of lost motion are provided between the tangs 82 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 :

8~ii slidin(3 engayement 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 48 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 sllding 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.

Claims (7)

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

1. A slack adjuster for a brake mechanism, said slack adjuster comprising: a housing having inner and outer ends, a longitudinally extending rod having external threads thereon mounted in said housing, a rotatable nut on said rod having threaded engagement therewith, a non-rotatable longitudinally moving actuating member abutting one side of said nut for ad-vancing said nut and rod longitudinally toward said inner end, means for biasing the combination of said nut and said rod in a rearward brake-releasing direction upon movement of said actua-ting member away from said inner end, a washer non-rotatably fixed to said rod with its outer portion wedged between said biasing means and said actuating member adjusting means for rota-ting the nut relative to said rod, thereby forwardly advancing said rod with respect to said nut when said actuating member is advanced, and said washer and biasing means being constructed and arranged to create a restraining torque exceeding a predeter-mined driving torque produced by said adjusting means during advance of said actuating member.

2. The slack adjuster of claim 1 including: means closing off the outer end of said housing, an access passageway in said closing off means leading to the end of said rod, and torque transmitting means on the outer end of said rod for manu-ally adjusting the position of said rod relative to said nut.

3. The slack adjuster of claim 2 wherein said torque transmitting means comprises an abutment member having one-way ratchet teeth and coaxially fixed to said push rod and wherein an annular ring having teeth thereon is coaxially fixed within said closing off means, said ratchet teeth being oriented such that said push rod can be manually retracted until said ratchet teeth engage said teeth on said annular ring.

4. The slack adjuster of claim 3 wherein said ring has flat side edge teeth therein surrounding said access passageway and said ratchet teeth are annularly arranged.

5. The slack adjuster of claim 1 wherein a peripheral portion of said nut is positioned between said washer and a shoulder on said actuating member.

6. The slack adjuster of claim 5 wherein the width of said peripheral portion of said nut is less than the distance between said shoulder and said washer when abutted by said actuating member to provide a predetermined clearance for un-restrained rotation of said nut during adjustment of said rod by said adjusting means.

7. The slack adjuster of claim 1 including a rotatable actuating shaft projecting out of the outer end of said housing, said shaft being journaled by said housing, rotary cam means in said housing for moving said non-rotatable longitudinally moving actuating member, said rotary cam means being driven by said rotatable actuating shaft, and said rotary cam means being sup-ported by said rotatable actuating shaft out of frictional engage-ment with said housing.