If its a commercial vehicle you'd be better off for replies in the cars section.
However! Without teaching you to suck eggs try this if you haven't already. A suitable sized jar with brake fluid in it. Slacken off the bleed nipple fix the bleed pipe [The type with none return valve on it not a plain tube unless there are two of you doing the job] on the nipple and submerge the other end in the fluid in the jar. Pump the breaks about 4 times but make sure after you check level in fluid chamber don't let that get too low or you will just be sucking in air. Top it up but not too high or as you pump it will over flow and fluid is a good paint stripper. Do this for each one you may have to bleed the back ones too. Two people the same procedure except one pumps the peddle holding the pedal down until the nipple is re-tightened for each wheel and the other does the loosening and tightening of the nipples and keeps the chamber topped up. If that doesn't solve the prob then it could be shear conincidence your master cylinder rubbers have also go and need replacing. Many forget they have to put the bleed tube in fluid to prevent air getting back in through the tube.
If you have to bleed the lot then start from the cylinders at the back work to the last cylinder nearest the fluid chamber [told to me by a mechanic]
Rob, April 2008
