I'm having power brake problems, and am trying to isolate what is wrong - pump, hoses, or hydroboost unit. Basically, from time to time I find myself with the ability to slow down but not stop. I can stand on the brakes, and the truck will stop, but there's a chattering type feel through the pedal, like it's trying to grab but doesn't.

I found instructions on line to troubleshoot the system, but to be honest I followed those instructions and still couldn't figure out what was wrong. Those instructions were asking me to tell if the power assist was there after so many pedal stroke or so much time (IIRC), but I couldn't tell any difference in pedal feel. Even driving down the road when the problem occurs, the pedal feels the same except there's no stopping power. It's not like old vacuum assist systems, where it's like stepping on a rock if the power assist fails.

The truck has always had a "loose belt" sort of sound from the steering during cold weather, but until recently the brakes seemed to be unaffected by that. Last weekend I tried "changing" the PS fluid by cycling two quarts of new fluid through using the turkey baster method. That was no help at all.

I'm trying to avoid throwing money at the problem and replacing parts that are good. Can anyone comment on a good way to figure out what is failed/failing on my 2002 2500 CTD truck?

Thanks in advance for any help,