My rear brakes are sometimes touchy... I replaced a part called a RAPS valve, didnt work.. My question is.. is the porportion valve built-in the master cylinder? Could someone help me please?!?:confused:

Its a 94 X-cab 4.0L

I think what you replaced was the RABS valve, or Rear Anti-lock Brake valve. I don't think anything after 1986 when the RABS system started has a proportioning valve. I suppose the RABS handles it. Did you bleed the brakes? You might check for oil or grease on the rear drums, they get really touchy when you have a rear axle seal leaking. A wheel cylinder leaking will do it too. I had a 90 that would lock the right rear up if you looked at it when the wheel cylinder started leaking.