I have a 99 f350 dually crew cab diesel, the abs light is intermittently on, when braking, as the truck gets below 10 mph the brake pedal dives about an inch, then pushes back against my foot, then dives slightly again. very scary during panic stops, the stopping power is decreased when this happens. i have replaced all the pads, cleaned the front sensors. could it be the hydrobooster? or sensors? or abs unit? or maybe air in the system? although the fluid has never been low. while installing the front pads i made the mistake of turning the steering wheel without starting the motor, this caused power steering fluid to leak out of the pump cap, when i restarted the motor it sucked air from low fluid level, this caused the hydro booster to make noise when applying the brakes, didn't drive it, added fluid, took several miles and turning to elininate noise. could this have damaged the hydrobooster?

thanks for any suggestions

 

Might still have traped air in hydo. system. The fluid tends to foam up with air and it might take a while to get it all out. Have yopu been keeping an eye on the level. might have gone down some after the air purged. Hydroboost systems are always a little funky and with ABS added you really complicate things. The fact that you get an ABS light says alot. Might want to pull codes and see what the light is all about.