it works for me pbp3 pic16f1825 // ds1307 // pcf8574a either your code is wrong or your not connecting things properly

tested at 8mz an 32mhz the pcf8574a has no problem

Code:
                            
#CONFIG
   __config _CONFIG1, _WDTE_ON    & _FOSC_INTOSC   &_MCLRE_ON    &_PWRTE_ON 
   __config _CONFIG2,              _LVP_OFF   & _PLLEN_ON
#ENDCONFIG
         DEFINE OSC 32
         
            pkt var byte[11]
          MONTH VAR pkt[5]
          DATE  VAR pkt[4]
          HOUR  VAR pkt[2]
          MINS  VAR pkt[1]
          DOW VAR pkt[3]
          YEAR VAR pkt[6]
           SEC VAR pkt[0]
           cnt var byte

  
     osccon=$70    '8 MHz or 32mhz
         anselA=0        'dig i/o 
         ANSELC=0
      TRISC= 111111
       TRISA= 111110
       
   
     SDA         VAR PORTc.4       ; I2C Data pin
     SCL         VAR PORTc.3     ; I2C Clock Pin
pcf_Addr CON $78
rtc_Addr CON $d0       
      
       i2cwrite  sda,scl,rtc_Addr,0,[$80,$14,$11,3,$14,1,$14]  'SANE TIME AND DATE  
        i2cwrite  sda,scl,rtc_Addr,0,[$80]    'FORCE START IF REQ
        i2cwrite  sda,scl,rtc_Addr,0,[0]
 
  main:
  pause 2000
  i2cREAD  sda,scl,rtc_Addr,0,[str pkt \7 ]
  serout2 porta.0,84 ,[HEX HOUR,":", HEX2 MINS, ":",HEX2 sec, " - ", HEX DATE,"/", HEX MONTH  ,13,10]
  i2cwrite  sda,scl,pcf_Addr,0,[cnt]
  cnt=cnt+1
 goto main