RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/552,458, filed Oct. 24, 2006, entitled “Master Cylinder Lever with Independently Variable Rest Position and Engagement Point,” which is a continuation of U.S. patent application Ser. No. 10/966,737, filed Oct. 15, 2004, entitled “Master Cylinder Lever for a Hydraulic Disc Brake Having a Backpack Reservoir,” now U.S. Pat. No. 7,178,646, which is a continuation of U.S. application Ser. No. 10/316,452, filed Dec. 10, 2002, entitled “Master Cylinder Lever for a Hydraulic Disk Brake Having a Backpack Reservoir”, now abandoned, which application claims priority from U.S. Provisional Patent Application Ser. Nos. 60/344,450, filed Dec. 28, 2001; 60/416,130, filed Oct. 4, 2002; and 60/416,698, filed Oct. 7, 2002, each entitled “Master Cylinder Lever for Hydraulic Disc Brake.” 
    
    
     TECHNICAL FIELD 
     The present invention is directed toward an improved master cylinder lever for a hydraulic disc brake, and more particularly to a master cylinder lever having a variable dead band and variable rest position that can be varied independently of each other. 
     SUMMARY OF THE INVENTION 
     A first aspect of the invention is a method of adjusting a lever actuated bicycle hydraulic disc brake master cylinder. The disc brake master cylinder has a housing defining a cylinder having first and second ends and a port communicating with a fluid reservoir between the first and second ends. A piston is received in the cylinder and the piston has a seal having a leading seal edge between the piston and the cylinder. The lever is operatively associated with the piston to move the piston from an unactuated position with the leading seal edge a select distance between the port and the first end of the cylinder to an actuated position between the port and the second end of the cylinder. The method of adjusting the lever actuated bicycle hydraulic disc brake master cylinder comprises varying the select distance between the port and leading edge of the seal with the piston in the unactuated position and providing a stop preventing the leading edge of the seal from moving between the port and the second end of the seal as a result of varying the select distance between the port and the leading edge of the seal with the piston in the unactuated position. 
     A second aspect of the invention is a master cylinder for a bicycle hydraulic disc brake. The master cylinder comprises a housing defining a cylinder, the cylinder having a first and a second end. A hydraulic fluid reservoir is associated with the housing. A port is provided between the hydraulic fluid reservoir and the cylinder for providing fluid communication between the hydraulic fluid reservoir and the cylinder. The port has a port opening located between the first and second ends of the cylinder. A piston is received in the cylinder and has a seal operatively associated therewith. The seal has a leading edge and the leading seal edge is moveable between a select starting position with the leading seal edge between the first end and the port opening with the leading seal edge a select distance from the port opening and a pressurized position with the leading seal edge between the port opening and the second end, the leading seal edge preventing fluid flow between the cylinder and the reservoir when positioned between the port opening and the second end to pressurize the second end. A lever is pivotably attached to the housing and is operatively associated with the piston to move the leading seal edge between the select starting position and the pressurized position as the lever is pivoted between a rest position and a fully actuated position. A dead band adjustment mechanism is operatively associated with the piston for moving the leading seal edge to adjust the select distance between the port opening and the leading seal edge. The dead band adjustment mechanism is configured to prevent the leading edge of the seal from crossing the port opening as a result of dead band adjustment. The dead band adjustment mechanism may be further configured to substantially prevent varying of the rest position of the lever as a result of dead band adjustment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  is a perspective view of a first embodiment of a master cylinder lever for a hydraulic disc brake in accordance with the present invention; 
         FIG. 2  is an exploded view of the backpack reservoir of the master cylinder lever of  FIG. 1 ; 
         FIG. 3  is a cross-section of the master cylinder lever of  FIG. 1  taken along line  3 - 3  of  FIG. 1 ; 
         FIG. 4  is an exploded view of the piston train of the master cylinder lever of  FIG. 1 ; 
         FIG. 5  is an exploded perspective view of a socket receptacle spaced from a lever handle of the master cylinder lever of  FIG. 1 ; 
         FIG. 6  is an exploded view of the lever handle attachment assembly of the master cylinder lever of  FIG. 1 ; 
         FIG. 7  is a side elevation view of the master cylinder lever of  FIG. 1 ; 
         FIG. 8  is a cross-section of the master cylinder lever of  FIG. 1  taken along line  8 - 8  of  FIG. 7 , illustrating an adjustable lever pivot assembly; 
         FIG. 9  is an alternate embodiment of the adjustable lever pivot assembly of  FIG. 8 ; 
         FIG. 10  is a perspective view of a second embodiment of a master cylinder lever for a hydraulic disc brake in accordance with the present invention; 
         FIG. 11  is an exploded view of the backpack reservoir of the master cylinder lever of  FIG. 10 ; 
         FIG. 12  is a cross-section of the master cylinder of  FIG. 10  taken along line  12 - 12  of  FIG. 10 ; 
         FIG. 13  is an exploded view of the piston train of the master cylinder lever of  FIG. 10 ; 
         FIG. 14  is a perspective view of the push rod and threaded insert of the master cylinder lever of  FIG. 10 ; 
         FIG. 15  is a side elevation view of the master cylinder lever of  FIG. 10 ; 
         FIG. 16  is a schematic representation of the geometry of the lever of the present invention; 
         FIG. 17A  is a schematic representation of the geometry of a Brand B lever; 
         FIG. 17B  is a schematic representation of the geometry of a Brand A lever; 
         FIG. 18  is a schematic representation of the geometry of a Brand C lever; 
         FIG. 19  is a schematic representation of the geometry of a Brand D lever; 
         FIG. 20  is a graph of additional force required from a user&#39;s finger (%) versus lever travel from an engagement point for several brands of hydraulic levers as compared to the lever of the present invention; 
         FIG. 21  is a graph of a percentage of power to a lever versus lever travel for the lever of the present invention versus several known levers; 
         FIG. 22  is a plot of lever travel versus degrees deviation from perpendicular of finger force; 
         FIG. 23  is a cross-section of an alternate embodiment of the lever of  FIG. 12 ; 
         FIG. 24  is an exploded view of the lever of  FIG. 23 ; and 
         FIG. 25  is a cross-section taken along line  25 - 25  of  FIG. 23 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A first embodiment of master cylinder lever assembly  10  is illustrated in a perspective view in  FIG. 1 . The master cylinder lever assembly consists generally of a cylinder housing  12  having a bar clamp  14  at one end and a lever handle  16  pivotably attached at an opposite end. Also seen in  FIG. 1  is a reservoir cover  18  which covers a “backpack” reservoir which will be described in greater detail below. Also visible in  FIG. 1  is a contact point adjustment knob  20  which is also described in greater detail below. The master cylinder housing  12  is hydraulically connected to a slave cylinder which operates a hydraulic caliper (not shown) by hydraulic line  22 . 
       FIG. 2  is an exploded view of the “backpack” reservoir of the master cylinder lever of  FIG. 1 . The backpack reservoir consists of a reservoir chamber  28  defined in a rear facing portion of the master cylinder housing  12 . A cylinder wall  30  defining in part the cylinder of the master cylinder housing  12  extends into the reservoir chamber  28  and defines in part a first wall  31 . Extending through the cylinder wall between the reservoir chamber  28  and the master cylinder is a timing port  32  and a compensating port  34 . A pair of bosses  36  extend axially of the cylinder wall  30  on opposite sides of the timing and compensating port  32 ,  34 . A side wall  37  extends from the first wall. A diaphragm  38  made of an elastomeric material such as silicon rubber is made to overlay the side wall  37  and cover the reservoir chamber  28 . Thus, the first wall  31 , the side wall  37  and the diaphragm  38  define the reservoir chamber  28 . The diaphragm  38  has an expansion protrusion  40  extending therefrom opposite the reservoir chamber. A reservoir frame  42  is configured to receive the periphery of the diaphragm  38  to maintain a tight seal between the diaphragm  38  and the reservoir chamber  28 . This seal is promoted and the assembled relationship maintained by four screws  44  received in corner holes of the reservoir frame  42  and diaphragm  38  and threadably engaged with corresponding holes in the master cylinder housing  12 . A vanity cover  46  snap fits over the diaphragm and frame to both provide an aesthetic appearance and to protect the diaphragm  38 . 
     Locating the timing and compensating ports  32 ,  34  on the cylinder wall  30  as illustrated in  FIG. 2  essentially eliminates the possibility of air entering either of the timing or compensating ports regardless of the position of the master cylinder. As should be apparent to one skilled in the art, this is because air will always rise and the curved surface of the cylinder wall always cause air bubbles to be deflected away from the timing and compensating ports regardless of the position of the master cylinder. While in the preferred embodiment illustrated herein, the cylinder wall  30  is truly cylindrical, it could also have other configurations such as a triangular configuration with the ports located at the apex of the triangle which would have the same affect of preventing air bubbles from collecting in the vicinity of the timing or compensating ports. Any other profile of the cylinder wall or location of the ports on the cylinder wall which prevents collecting of air bubbles in the vicinity of the timing and compensating ports is considered to be within the scope of the invention. The bosses  36  are provided to prevent the diaphragm  38  from covering and inadvertently sealing the compensation or timing ports as hydraulic fluid is drawn into the compensating and timing ports. As would be apparent to those skilled in the art, the bosses  36  could be replaced with similarly positioned posts or the like or other extensions to perform the same function of keeping the diaphragm spaced from the ports and such other configurations may have an additional advantage of minimizing the potential of air bubbles collecting in the vicinity of the ports. This structure facilitates a single lever being used on either a right or left portion of a handle bar without risk of bubbles entering the hydraulic fluid line. 
       FIG. 3 , a cross-section of the master cylinder, illustrates the piston train  49  operatively associated with the cylinder  50  of the master cylinder housing  12 . The cylinder  50  has a first end  51  and a second end  52 .  FIG. 4  illustrates the piston train  49  in an exploded view and the same reference numbers will be used to identify like elements in  FIG. 3  and  FIG. 4 . 
     The piston train consists of a piston  54  received in the cylinder  50  having an annular cup or umbrella seal  56  abutting an internal portion of the piston  54 . A compression spring  60  biases the piston  54  toward the first or open end of the cylinder  51 . An “O” ring  62  forms a lower seal on the piston and is received within an annular recess in the piston. A hex spacer  64  has leading protrusion  66  with an annular detent that is snap fit into a corresponding female receptacle  68  in a trailing end of the piston  54 . This snap fit allows for relative rotational movement between the piston and the hex spacer  64 . The hex spacer  64  is in turn received in a hex hole  70  of contact point adjustment knob  20 . The knob  20  also has a leading externally threaded extension  72  which threadably engages a countersink  74  concentric with and external of the cylinder  50 . A male pushrod  76  having an externally threaded shaft  78  at its first end and a ball head  80  at its second end with posts  82  extending in opposite directions therefrom is snap fit received in a slotted socket  84  on an end opposite the protrusion  66  of the hex spacer  64  with the post  82  received in the slots  86 , as best seen in  FIG. 3 . The male pushrod  76  in turn is threadably engaged with a female pushrod  86  having an internally threaded cylinder  88 , again best viewed in  FIG. 3 . The female pushrod also includes a ball head  90  having oppositely extending posts  92 . A socket insert  94  has a leading ball socket  96  with opposite slots  98  for snap fit receiving the ball head  90  with the posts  92  received in the corresponding slots  98 . The socket insert  94  also includes locking posts  100 . Referring to  FIG. 5 , these locking posts are received within a keyed orifice  102  in the lever handle  16  and then rotated 90° to lock the posts  100  in the annular slot  104 . Referring back to  FIG. 3 , a dust cover  106 , which is preferably elastomeric, is engaged in an annular slot  108  of the knob  20  with a nipple end receiving the female pushrod  86  as shown. 
     The basic operation of the master cylinder is well understood by those skilled in the art. Referring to  FIG. 3 , pivoting the lever handle  16  upward from a rest position toward the cylinder housing causes the piston train  50  to drive the piston upward within the cylinder. As the piston moves upward in the cylinder the cup or umbrella seal  56  covers the timing port  32  which pressurizes the fluid within the hydraulic line  22  at the second end of the cylinder and which in turn actuates a slave cylinder within a hydraulically coupled brake caliper (not shown). When the lever handle  16  is released, the compression spring  60  biases the piston toward the first end of the cylinder to reassume the position shown in  FIG. 3 . The distance between the cup seal  56  and the timing port  32  is referred to as the “dead-band.” During the part of lever actuation where the cup seal is between the timing port  32  and the first end of the cylinder, fluid in the reservoir between the seal and the timing port returns to the reservoir chamber  30 , perhaps causing expansion of the expansion protrusion  40  of the diaphragm  38 . During this part of lever actuation, the second end of the cylinder cannot be pressurized. It is highly desirable to be able to adjust the length of the dead-band in accordance with user preferences. Rotation of the contact point adjustment knob  20  in a first direction allows for the dead-band to be taken up and reduced and rotation in a second direction increases the dead-band. In  FIG. 3  a maximum dead-band is shown because the knob is almost fully threaded from the countersink  74 . Threading the knob into the countersink causes the piston to move upward, thus reducing the dead-band. Obviously, the hex engagement between the hex spacer  64  and the knob  20  causes the hex spacer to rotate with the knob. However, the snap fit between the protrusion  66  and the female receptacle  68  of the piston prevents the piston from rotating relative to the knob, minimizing impairment of the seals. 
     One highly advantageous aspect of this design is that as the knob is screwed inward in the first direction, the male pushrod rotates axially because of engagement between the posts  82  and the hex spacer. The threads between the male pushrod  76  and the female pushrod  86  are configured to cause the male pushrod to extend further from the female pushrod as a result of this axial rotation in the first direction. The respective threads of the knob and the pushrods are designed such that the net result is that the lever handle does not move relative to the housing as the knob is turned. This feature has the important advantage of maintaining a preselected start position of the lever resulting reach between the lever and the handlebar as the dead-band of the master cylinder is adjusted. 
     In the event a user wishes to adjust the reach of the lever (that is, the distance between a handle bar and the lever at the rest position), this can be done independently of the dead-band adjustment by pivoting the handle away from the caliper housing to disengage the snap fit between the ball head  90  and the ball socket  96  of the socket insert  94 . Once disengaged, the female pushrod  86  maybe rotated about its axis to extend or retract the female pushrod relative to the male pushrod to adjust the reach as desired. While the current embodiment may allow adjustment in 180° increments, other configurations allowing smaller increments of variation or perhaps event infinite variation of the lever reach are within the possession of those skilled in the art and within the scope of the invention. 
       FIG. 6  is an exploded view of the lever pivot assembly  110  of the first embodiment of the master cylinder lever of  FIG. 1 . The lever pivot assembly  110  consists of an axial bore  112  about which the lever handle  16  pivots. A threaded hole  114  perpendicularly intersects the bore  112 . A slotted bushing  116  (preferably made of plastic) which is part of a bushing plate  118  extends into each end of the bore  112 . A female bolt  120  is received through one slotted bushing while a male bolt  122  is received through the other slotted bushing so that they threadably engage within the bore  112 . As perhaps best seen in  FIG. 8 , the slotted bushings  116  each have annular camming tapers  124  between smaller and larger diameter portions of the bushing. A head of the female bolt  120  similarly has a camming taper which mates with the camming taper  124  of the bushing. Likewise, the male bolt has a cammed surface which mates with a corresponding cammed surface of its corresponding bushing. Referring to  FIG. 8 , as should be apparent to one skilled in the art, as the male bolt is threaded into the female bolt in the assembled configuration, the cam relationship causes the bushings to expand radially as the bolts are drawn axially together. This causes any “slop” in the pivotal connection between the lever handle and the caliper housing to be taken up. A lock screw  130  is threadably received in the threaded hole  114  and, as illustrated in  FIG. 8 , can be threadably inserted in the hole to lock the male and female bolts in their select position. As the pivot wears the lock screw  130  can be backed off and the female and male bolts more tightly threadably engaged to pickup any slop. 
       FIG. 9  is an alternate embodiment of the adjustable lever pivot assembly  110 ′. This embodiment differs in that the male bolt has a portion having an outer diameter equivalent to the outer diameter of the female bolt illustrated at  132  and the female bolt does not extend as far axially as the embodiment illustrated in  FIG. 8 . A gap  134  is provided between this enlarged diameter  132  of the male bolt  122 ′ and the female bolt  120 ′. In this embodiment, the lock screw  130  directly engages each of the male bolt  122  and the female bolt  120  which may provide more secure locking although it may not provide as much axial adjustment from either end of the lever. 
       FIG. 10  is a second embodiment of a master cylinder lever for a bicycle hydraulic disc brake  200  of the present invention. The second embodiment of the master cylinder lever assembly  200  consists of a cylinder housing  202  having a bar clamp  204  at one end and lever handle  206  pivotably attached to the housing at an opposite end. A reservoir housing  208  covers a hydraulic fluid reservoir  210  which will be discussed in greater detail below. Also visible in  FIG. 10  is a worm knob  212  used to adjust the lever dead-band in a manner that will be discussed in greater detail below. The master cylinder housing  202  is hydraulically connected to a slave cylinder which operates a hydraulic caliper (not shown) by hydraulic line  214 . 
       FIG. 11  is an exploded view of a “backpack” reservoir of the master cylinder lever of  FIG. 10 . The backpack reservoir of  FIG. 11  is identical in its configuration to the backpack reservoir of  FIG. 2  except it is oriented substantially horizontally within the lever housing whereas the backpack reservoir of the first embodiment of the master cylinder lever of  FIG. 1  is oriented vertically. The same reference numbers are used to describe like elements and the detailed description of these elements is provided above with reference to  FIG. 2 . 
       FIG. 12  is a cross-section the master cylinder lever assembly of  FIG. 10  taken along line  12 - 12  of  FIG. 10 .  FIG. 12  illustrates a piston train  220  received within a cylinder  222  defined within the hydraulic cylinder housing  202 . The cylinder  222  has a first end  224  and a second end  226 . A threaded countersink  225  in the housing  202  abuts the second end  226  of the cylinder  222 , coaxial with a longitudinal axis of the cylinder.  FIG. 13  illustrates the piston train  220  in an exploded view and the same reference numbers will be used to identify like elements in  FIGS. 12 and 13 . 
     The piston train  220  consists of a piston  228  within the cylinder  222 . The piston  228  has a first annular cup or umbrella seal  230  near a leading end and a second annular cup or umbrella seal  232  near a trailing end. A push rod  234  has a threaded portion  236  at a first end and a head  238  at a leading second end. A leading portion of the head  238  defines a ball surface which is received in a corresponding cup surface  240  in a trailing end of the piston  220 . The threaded portion  236  of the push rod  234  is threadably engaged with the lever handle  206  in a manner that will be discussed in greater detail below. A hex orifice  241  is defined in the second end of the push rod and sized to fit an appropriate Allen wrench. A plurality of radial ribs  242  extend axially from a rear surface of the head  238  opposite the ball surface (see  FIG. 14 ). An externally threaded insert  244  has an externally threaded leading axial portion  246  and a trailing axial portion  248  having radially inclined gear teeth which are best viewed in  FIGS. 13 and 14 . The threaded insert  244  further has an axial bore  250  having conical side walls. The bore  250  opens at the first end to an annular pocket  252  having axially extending teeth  254  configured to mate with the radial ribs  242  which extend axially from the rear surface of the head  238  (See  FIG. 14 ). Externally threaded insert  424  further includes a rearward facing pocket  256  receiving an elastomeric annular wipe seal  257  having a nipple which forms a seal with the push rod  234 . 
     A worm  258  is received in the housing along an axis transverse an axis of the cylinder. The worm  258  has a threaded shaft  259  and a worm knob  212 . The threads  259  of the threaded shaft threadably engage the radially inclined teeth  248  of the externally threaded insert  244 . A C-clamp (not shown) or the like secures the worm  258  within the transverse bore in the housing by engaging an annular groove  261  in the distal end of the threaded shaft  259 . 
     A coil spring  262  resides between a second end  226  of the cylinder and a leading end of the piston  228  to bias the piston toward the first end  224 . The coil spring also compresses the radial ribs  242  of the push rod head  238  into mated engagement with the axially extending teeth  254  of the threaded insert  244  so the push rod  234  rotates axially as the threaded insert is rotated. 
     The lever handle  206  may be pivotably attached to the housing by lever pivot assembly described above with reference to  FIGS. 6 and 8 . Alternatively, a conventional pivot coupling may be used. Spaced from the lever pivot assembly  110 , is a bore  264  in the lever along an axis parallel to the axis of the lever pivot assembly and transverse the axis of the cylinder  222 . A cross dowel  266  is received in the bore  264 . The cross dowel  266  includes a threaded bore  268  transverse the dowel axis. Referring to  FIG. 12 , this threaded bore  268  threadably receives the threaded portion  236  at the first end of the push rod  234 . 
     The basic operation of the master cylinder lever  200  of  FIG. 12  is similar to that of the first embodiment of the master cylinder lever  10  discussed above with reference to  FIG. 3 . The lever handle  206  is shown at a rest position in  FIG. 12 . As the lever is pivoted upward toward the bar clamp  204  and toward a fully actuated position, the push rod  234  is driven forward which in turn causes the piston  228  to move toward the second end  226  of the cylinder  222 . As the piston  228  moves toward the second end  226  of the cylinder  222  the leading cup or umbrella seal  230  covers the timing port  32  which prevents flow of fluid from the cylinder into the reservoir and causes build up of pressure in the second end of the hydraulic fluid cylinder which in turn pressurizes fluid within the hydraulic fluid line  22  and which in turn actuates a slave cylinder within a hydraulically coupled brake caliper (not shown). When the lever handle  16  is released, the compressing spring  262  biases the piston  228  toward the first end  224  of the cylinder to reassume the position shown in  FIG. 12 . Pivoting of the push rod  234  about the head  238  by pivoting of the lever handle  206  is accommodated by the conical side walls of the axial base  250 . 
     The distance between the cup seal  230  and the timing port  32  is referred to as the dead-band. As described above with reference to  FIG. 3 , during the part of lever actuation where the cup seal is between the timing port  32  and the first end of the cylinder, fluid in the reservoir between the seal and the timing port returns to the reservoir  30 . During this part of lever actuation, the second end of the cylinder cannot be pressurized. To adjust the length of dead-band, the piston can be advanced in the cylinder by rotating the knob  212  in a first direction which in turn causes rotation of the threaded insert to threadably advance the threaded insert within the threaded countersink  225  along the cylinder axis, thereby advancing the piston toward the second end of the cylinder. Turning of the knob  212  in a second direction reverses the direction of the threaded insert to increase the dead-band. The ball and socket connection between the cup  240  at the trailing end of the piston and the ball at the leading end of the head  238  of the push rod  234  prevents the piston from rotating relative to the threaded insert which helps maintain the integrity of the seals. 
     The second embodiment of the hydraulic cylinder lever of  FIG. 12  also includes a structure for compensating for movement of the push rod during dead-band adjustment to maintain the lever  206  in a select rest position. The threads between the threaded portion  236  of the push rod and the threaded bore  268  of the cross dowel  266  are configured to counteract pivoting of the handle that would otherwise occur about the lever pivot assembly  110  when the push rod  234  is moved by movement of the threaded insert  244 . In other words, as the threaded insert  244  is advanced toward the second end of the cylinder, which necessarily causes the advancement of the push rod  234  toward the second end of the cylinder and which would normally cause the lever handle  206  to pivot upward, the threaded engagement between the second end of the push rod and the cross dowel tends to move the lever handle  206  downward in an amount that corresponds to what would be the upward movement so as to maintain the lever handle  206  at a select start position. 
     In the event a user wishes to adjust the reach of the lever, this can be done independently of the dead-band adjustment. Insertion of an Allen wrench into the hex orifice  241  allows for axial rotation of the push rod  234 . However, the worm connection between the threaded insert  244  and the worm  258  prevents rotation of the threaded insert  244  by the push rod  234 . Because the threaded insert  244  is relatively fixed against rotation, turning of the push rod  234  causes disengagement between the radially extending ribs  242  of the head  238  and the complimentary axially extending teeth  254  in the externally threaded insert against the bias of the spring  262  and allows for pivotal movement of the lever handle  206  up or down in accordance with user preferences to provide a select reach. The teeth  254  and ribs  242  preferably have inclined, mating surfaces which define ramps facilitating this disengagement against the force of the bias of the spring  262 . Disengagement can be aided by pushing axially on the Allen wrench against the spring bias as the push rod  234  is rotated. 
     In a highly preferred embodiment, the axis of the threaded bore in the cross dowel is provided to not intersect with the cross dowel axis. This has the effect of locking the push rod in place relative to the cross dowel when a load is placed on the lever handle  206  so as to prevent relative rotation between the push rod  234  and the cross dowel  236 . This feature thereby prevents inadvertent variation of the lever reach during lever actuation. An off-set of between 0.01-0.04 inches between the axes has been found to be sufficient. 
       FIG. 15  is a side elevation view of a master cylinder lever of  FIG. 10 . This figure is used to illustrate an embodiment of a lever geometry which has been found to provide significant advantages in lever operation. The bar clamp  204  is designed to receive a handle bar  280  along a clamp axis  282 . The lever handle  206  is pivotably connected by lever pivot assembly  110  about a pivot axis  284 . In a highly preferred embodiment, the pivot axis is 39 mm from the clamp axis. The lever handle  206  defines a finger receptacle  286  configured to receive at least one finger of a user. In the embodiment illustrated in  FIG. 15 , the finger receptacle  286  is configured to receive two fingers of a user and effective finger force point  288  is defined by approximately the center of a typical user&#39;s two fingers. For the purpose of this application and the charts and calculations herein, the location of the finger force point is deemed to be 30.0 mm from the end of the lever when based on an estimate of an average user&#39;s finger size. A select finger actuation path is defined by arrow  290 , and extends from the effective finger force point  288  at an “engagement point” of the lever. As used herein, the “engagement point” means a point along the arc of lever actuation where the pads of a caliper operatively associated with the master cylinder lever begin compressing a disc therebetween. In other words, a point where the lever handle drives the piston train against operative fluid resistance. The select ideal finger actuation path  290  is a design criteria intended to estimate a typical finger path of a user of the brake in typical operating conditions. Based upon observations of users, the select ideal finger actuation path is at an angle θ90° or greater. In  FIG. 15  the angle θ is 96°, a best estimate of a typical average finger path. Actual finger paths may range from 90°-108°, or even greater than 108°. An arc  292  is defined by movement of the effective force point  288  as a lever is actuated between the engagement point position shown in  FIG. 15  and a fully actuated position with the effective force point  288  at point  288 ′ in  FIG. 15 . 
     In one embodiment of the invention illustrated in  FIG. 15 , the pivot axis  284  is preferably spaced from the clamp axis  282  a distance such that a chord between the points  288  and  288 ′ of the arc  292  substantially corresponds to the select ideal finger actuation path  290 . In this manner, a user experiences a mechanical advantage resulting from handle actuation that does not substantially decrease as the handle is pivoted between the at rest position and the fully actuated position. The angle of the chord between the point  288  and  288 ′ could actually be slightly less than the angle θ, but should be no less than 6° less than the angle θ so as to prevent an unacceptable loss of mechanical advantage. 
     The desired chord defined by the arc between the rest position and the fully actuated position of the effective finger force point is able to meet the criteria of substantially corresponding to an ideal finger actuation path in the range of greater than 96° if the pivot axis  284  can be brought close enough to the clamp axis  282 . In the embodiment illustrated in  FIG. 15 , this geometry is facilitated by locating the reservoir  208  and the cylinder  222  of the master cylinder lever housing generally parallel to the clamp axis  282 , and the pivot 39 mm from the clamp axis. Where the master cylinder is aligned vertically as with the first embodiment illustrated in  FIGS. 1-5 , it would be very difficult to meet these design criteria because the cylinder and reservoir reside between the pivot axis  284  and the clamp axis  282 . This is illustrated in  FIG. 7 . Here, the arc  292 ′ defined by pivotal movement of the effective finger force point  288  from the engagement point to the fully actuated position  288 ′ defines a chord  294 ′ that forms an angle less than 90° from the clamp axis  282 . However, the angle θ of the select ideal finger actuation path is greater than 90°, again preferably greater than 96°. As a result, a user would sustain a significant loss of mechanical advantage when trying to actuate the lever handle  206  along the select ideal finger actuation path  290 ′. 
       FIGS. 16-19  illustrate the geometry of a highly preferred embodiment of the present invention as compared to representative hydraulic master cylinder levers on the market in 2002.  FIG. 17A  is a Brand B lever geometry.  FIG. 17B  is a Brand A lever geometry.  FIG. 18  is a Brand C lever geometry.  FIG. 19  is a lever geometry of a Brand D hydraulic brake lever. 
     Beginning with  FIG. 16 , in a highly preferred embodiment of the present invention, the pivot axis  284  is 39 mm from the clamp axis  282 . For the purpose of this analysis, it is assumed that the engagement point is 50 mm from the clamp axis  282 , and is illustrated by the line  300 . The application of braking force from the engagement point to the conclusion of the lever movement is assumed to be 10 mm and is represented by the full actuation line  302 . Finally, for the purpose of this analysis, the assumed ideal finger actuation pad  290  is an angle θ 96° from the clamp axis. The effective finger force point  288  is 30 mm from the bar end. The arc  304  represents the effective finger force point travel as the lever is actuated. A chord drawn between the engagement line where the effective finger force point is located at the beginning of brake actuation and the point that the full actuation line  302  intersects the arc  304  is at 96°, equal to the ideal finger path angle θ. This provides for a minimal loss of mechanical advantage as the lever is actuated. 
     In  FIG. 17A  the Brand B lever has a pivot axis  284  53 mm from the clamp axis  282 . Again, assuming an engagement point  300  beginning 50 mm from the clamp axis and a full actuation line  302 , 10 mm from the engagement point, it can be observed that the arc  304  of travel of the effective finger force point  208  deviates inwardly from the ideal finger path  290 . The same is true in  FIG. 17B , where the Brand A lever pivot axis is 50 mm from the clamp axis  282 . As will be illustrated in the figures discussed below, this results in an increasing loss of mechanical advantage over the lever stroke. 
       FIGS. 18 and 19  represent the geometry of the Brand C and Brand D hydraulic brake levers respectively. Like numbers are used to identify like elements of these figures. Brand C, with the pivot axis located 63 mm from the clamp axis has a more pronounced deviation of the arc  304  from the ideal finger path  209  and thus, as will be illustrated below, has even a greater loss of mechanical advantage than the Brand B lever. Finally, the Brand D levers, with a pivot point 65 mm from the clamp axis, produces an even greater loss of mechanical advantage. 
       FIGS. 20 and 21  illustrate the respective mechanical advantage of the lever geometry of the present invention, designated as Avid, and the Brands A-D illustrated schematically above. Referring first to  FIG. 20 , the geometry of Brands A-D levers each will result in applying an additional amount of force to the lever along the ideal finger path over the course of the lever actuation. With respect to the Avid lever of the present invention, it can be seen that the geometry actually produces an increasing mechanical advantage over the first 5 mm of lever travel and then a slight decrease of mechanical advantage (less than 1%) over the final 5 mm of lever travel. Over the full range of lever travel, a net loss of mechanical advantage is zero. 
       FIG. 21  is essentially the inverse of  FIG. 20 . It illustrates that the geometries of the Brand A-D levers result in a loss of power over the actuation stroke. Again, the Avid lever of the present invention actually provides improved power through the first 5 mm with slightly decreasing power over the final 5 mm of travel and no change in the net amount of power applied to the lever between the engagement point and full actuation of the lever. 
       FIG. 22  illustrates where the loss of power comes from by comparing how far from perpendicular to the clamp axis the finger force is over the lever actuation stroke. For the geometry of the present invention (the Avid lever), the force begins 5 mm off, goes to perpendicular at about the center of the stroke and then returns to 5 mm off at the conclusion of the stroke. For Brands A-D, a significant deviation from perpendicular is present at the beginning of the stoke and increases from there. 
     As is apparent, the Avid lever geometry provides an increasing range of mechanical advantage over at least a portion of the lever actuation. In its broadest sense, the present invention can be characterized as the selection of a lever geometry having a pivot axis of 50 mm or less that is always equal to or closer to the clamp axis than the engagement point. This geometry produces a lever having an increasing mechanical advantage over at least a portion of the actuation stroke but does not encompass the geometry of the Brand A lever which is believed to be the lever having the pivot axis the closest to the clamp axis known in the art. 
       FIG. 23  is a cross-section of an alternate embodiment of the drive train of a master cylinder. The piston and cylinder of the embodiment of  FIG. 23  is essentially identical to that of the embodiment of  FIG. 12 , and like reference numbers followed by a prime (′) are used for like elements and described above in detail with respect to  FIG. 12 . The primary difference in the structures begins to the right of the surface  240 ′ in the trailing end of the piston  220 , which in  FIG. 23  is flat as opposed to a cup surface. 
     The embodiment of  FIG. 23  has push rod  400  having a threaded portion  402  at a first end and head  404  at a second end. The head  404  has a bore receiving a pin  406  transverse the axis of the pushrod  400 . The head  404  is received in a socket  408  within a piston coupling  410  having a leading flat surface  412  abutting the cup  240 ′. Referring to  FIG. 24 , the piston coupling  410  has axial slots  414  which receive the pins  406  to allow axial movement of the head  404  within the piston coupling  410 , but prevent axial rotation of the push rod  400  relative to the piston coupling  410 . The threaded portion  402  of the pushrod is threadably engaged with the lever handle  206 ′ in the same manner discussed above with respect to the embodiment of  FIG. 12 , including the off-center coupling with the cross-dowel. The piston coupling  410  has an annular flange  416  with sinusoidal florets  418  extending radially therefrom. An externally threaded insert  430  has an externally threaded leading axial portion  432  and a trailing axial portion  434  having radially inclined gear teeth which are best viewed in  FIG. 24 . Threaded insert  430  further has an axial bore  436  having sinusoidal florets  438  configured to mate with the sinusoidal florets  418  of the piston coupling  410 . An elastometric annular wipe seal  440  having a nipple  442  received in an annular groove  444  of the push rod  400  abuts the threaded insert  430 . 
     The lever of  FIG. 23  also includes a worm  258 ′ essentially identical to that of the embodiment discuss above with respect to  FIG. 12  and which will not be re-described here. Likewise, the pivot assembly  446  is similar to that described with reference to  FIG. 12 . 
     The basic operation of the master cylinder of  FIG. 23  is identical to that of the master cylinder lever  200  of  FIG. 12  and this description will not be repeated. The embodiment of  FIG. 23  shares the features of independent reach adjustment and a dead-band adjustment that compensates for and prevents change of the reach adjustment during dead-band adjustment and is not re-described here. The reach adjustment differs slightly from the embodiment discussed above with respect to  FIG. 12 . In the embodiment of  FIG. 23 , insertion of an Allen wrench into a hex socket  448  allows for reach adjustment. Axial rotation of the push rod by an Allen wrench will cause indexed axial rotation of the piston coupling  410  relative to the threaded insert  430 . The threaded insert  430  is prevented from axial rotation by the worm  258 ′. The axial slots  414  allow disengagement and relative movement of the florets and axial rotation of the piston coupling  410  relative to the push rod  400  is prevented by the pins  406  received in the slots  414 . In a preferred embodiment, each indexed rotation of the push rod causes a uniform movement of the lever end relative to the clamp axis (e.g., 1 mm). The mating florets are illustrated in  FIG. 25  in a cross-section taken along line  25 - 25  of  FIG. 23 . 
     The embodiment of  FIG. 23  also includes a feature to protect the piston train in the event of an accident causing movement of the lever handle  206  away from the clamp axis. In such an event, the head  404  of the push rod can axially disengage from the socket  408  of the piston coupling in a direction to the right. Once a user recovers from such a mishap, the lever can be simply returned to its normal rest position which will cause the head  404  to pop back into the socket  408 .
A method of adjusting a lever actuated bicycle hydraulic disc brake master cylinder. The disc brake master cylinder has a housing defining a cylinder having first and second ends and a port communicating with a fluid reservoir between the first and second ends. A piston is received in the cylinder and the piston has a seal having a leading seal edge between the piston and the cylinder. The lever is operatively associated with the piston to move the piston from an unactuated position with the leading seal edge a select distance between the port and the first end of the cylinder to an actuated position between the port and the second end of the cylinder. The method of adjusting the lever actuated bicycle hydraulic disc brake master cylinder comprises varying the select distance between the port and leading edge of the seal with the piston in the unactuated position and providing a stop preventing the leading edge of the seal from moving between the port and the second end of the seal as a result of varying the select distance between the port and the leading edge of the seal with the piston in the unactuated position.