I agree with Trop A Cal about flushing the HydroBoost...but I am not a fan of the turkey baster method. While you will be introducing new fluid with old as the new is pumped through the system and pushing the old back to the same reservoir. If you head over to the Duramax Forum and
Click Here. This is the best How To i've read on it yet.
Then next thing I have learned about my 3 DRW's is that if the brake fluid is black...it needs to be flushed...twice! I use the common bleed process at the furthest wheel first and go until you have clean fluid. After you complete the second bleed, replace all the rubber lines with Russell Stainless ones. If the fluid got hot enough to turn black, it usually destroys the rubber lines. In a panic stop the rubber lines will swell and not provide good pressure to the calipers/wheel cylinders. (My 99 had rear drums and I assume your 2000 has them as well.) If you do have drums and have to pull the axles to service the brakes, I recommend replacing the seals with GM seals. I never had any luck with aftermarket seals, and DO NOT re-use the old ones.
