1. Welcome to PlowSite. Notice a fresh look and new features? It’s now easier to share photos and videos, find popular topics fast, and enjoy expanded user profiles. If you have any questions, click HELP at the top or bottom of any page, or send an email to help@plowsite.com. We welcome your feedback.

    Dismiss Notice

Dirty brake fluid

Discussion in 'Chevy Trucks' started by CSC Contracting, Jan 30, 2010.

  1. CSC Contracting

    CSC Contracting Senior Member
    Messages: 105

    What would make my brake fluid on my 91 GMC 3500 black and dirty? Any easy way to drain all fluid and replace? Thanks
  2. Sydenstricker Landscaping

    Sydenstricker Landscaping PlowSite Veteran
    Messages: 3,882

    Just the general use and abuse of the fluid. Most people dont realize they should change that as well. Check all the lines and make sure they arent all rusted and swollen, that could cause that. Also the insides of the rubber flex lines could be deteriorating and causing the fluid to turn black. But more than likely that fluid has been there since 1991. Best way I found was get all the old fluid out of the reservoir and refill with new. Then just bleed each wheel cylinder until clean fluid comes out, you will see the difference!!! Just make sure to bleed one wheel, and check/refill the reservoir. That way will ensure you dont run it dry and get a buttload of air in the system
  3. sweetk30

    sweetk30 PlowSite.com Addict
    Messages: 1,588

    DONT run all that fluid threw the master to blead it out.

    seen to many masters die after that. then thay get a new one.

    use a turkey baster or somthing like that. pull it all out and wipe out with rag.

    refill and full blead out is best from there.

    and check lines and hoses like others have said.

    and 88-up gm behind gas tank pop a lot.
  4. 2COR517

    2COR517 PlowSite Fanatic
    Messages: 7,115

    Definitely use the turkey baster. Fill it with new fluid and bleed away. If you have the patience, just let them bleed with gravity. RR first, will take the longest. LR will be real quick after that. RF, finish up with LF.
  5. Matt400

    Matt400 Senior Member
    Messages: 164

    Its probably been in there too long, whats worse than the color is having too much moisture in the fluid which lowers the boiling point that leeds to brake failure when they get hot if you use them hard.

    The make up of brake fluid is designed to attract and suspend moisture other wise you would have water collecting at the lower points- bottom of calipers.
    A nice tool for the job is this one where you can vacuum out the master cylinder using compressed air "if you have it" and then pull a vacuum on the bleeders while keeping the reservoir full.
  6. lawnmedic

    lawnmedic Senior Member
    Messages: 703

    I'm not a fan of just using the bleeders to change out the fluid. The bleeder is at the highest point in the cylinders/calipers. This lets all the gunk in the lines settle into the bottom of them. If the fluid is bad then the cylinders/calipers need to be disassembled and cleaned also.
  7. 2COR517

    2COR517 PlowSite Fanatic
    Messages: 7,115

    That's a real good point. I just pulled a wheel cylinder off one of my vehicles. I was amazed how nasty it was. Calipers the same way......
  8. CSC Contracting

    CSC Contracting Senior Member
    Messages: 105

    Thanks for the help guys. Changing the fluid today. I have had over 20 plow trucks and have never thought to change the brake fluid.
  9. Sydenstricker Landscaping

    Sydenstricker Landscaping PlowSite Veteran
    Messages: 3,882

    Dont forget to check the blinker fluid too:D:laughing:
  10. 2COR517

    2COR517 PlowSite Fanatic
    Messages: 7,115

    Use the winter blend this time of year:rolleyes: