Hi I am new to the bbs, so thanks for any help in advance.

I have a 89 f350 dually diesel that when you first hit the brakes they go almost to the floor but the front brakes grab, one pump or lightly lifting the pedal and the brakes are hard as a rock feels like rears only, Has a new master cylinder, any ideas or have you had this problem before, Thanks,

 

check you vacum linefor leaking,or the vacum pumpcould be goingbad. you might pull the back drums off and clean the adjusters they might be froze up from rust.

 

Another quick ? to get a better understanding. Do your brakes remain tight if you do not move vehicle. IE if you pump them up and pedal gets tight can you walk away for a minute and come back and have tight pedal on 1st pump? If this is the case I have seen front wheel bearings get loose enough to cause rotor to push piston back in caliper in front requiring 2 pumps to get solid pedal. Check wheel bearings for movement. Also need to verify that all air is removed from brake lines from M/C install. 3rd I would verify brake adjustment on rear drums. Could also b a bad M/C even though it is new.