Master Cylinder Reservoir Cleaning

Discussion in 'General Chevy & GM Tech Questions' started by Stretch56, Aug 11, 2014.

  1. Stretch56

    Stretch56 Member

    Has anyone pulled their MC off their GM and cleaned it because of slime buildup? If so, what method of cleaning did you use, i.e. soap & water, dishwasher, alcohol etc.
  2. The Heater

    The Heater Rockstar 100 Posts

    Hello, sir:

    First thing you do is clean it with Brake Clean or some other low boiling point chlorinated solvent (wear a vapor respirator). You can also clean it first with WD-40, but you have to remove the residue, whereas with a low vapor pressure (low boiling point) solvent, this is not an issue. Blow out all channels with compressed air.

    Next, take it apart completely. Make sure you have the correct parts to rebuild it. Kits can be purchased from NAPA or from the dealer to rebuild the master cylinder, and they usually include a spring, one or more seals, possibly other parts. At this point you can wash the unit in hot water with TSP and a bit of dish detergent added for suds. Rinse thoroughly, blow out with compressed air, then clean again with the low boiling point solvent to remove all traces of water, blow out the passages with compressed air, assemble with your new parts, and put it back in, bleed the system (you may need to disable the proportioning valve in the system) of air, and away you go.
  3. Stretch56

    Stretch56 Member

    Thank you for responding.

    I was planning on just removing the plastic fluid reservoir from the Master Cylinder and cleaning the gunk out of that. I just did a flush / bleed on the brakes last weekend and the pedal pumped up fine. My old fluid was so dark, that I didn't realize the slime had adhered to the inside of the plastic reservoir. Now that the fluid is clear, my reservoir is streaked with black lines, so it's difficult to see the fluid levels from the outside. I don't want to replace the reservoir because it's $88 from Rock Auto for OEM, and a complete MC is $150.

    I've found several posts for cleaning the reservoir, ranging from running it through the dishwasher or filling it with soap & water along with small washers or ball bearings and shaking it to agitate the slime loose, using a toothbrush or bottle brush, brake cleaner etc.

    I think with the brake fluid migration issue, most of the gunk should be in the reservoir and if I clean that and do one more good power bleed, it should be golden. I'm just trying to form a consensus on which cleaning method is the best.

    Thanks again
  4. Crawdaddy

    Crawdaddy All hail the Mad King!! Staff Member 5+ Years 1000 Posts Platinum Contributor

    I don't think I'd use any water-based cleaning methods on it. Water and brake fluid do not mix.
  5. Stretch56

    Stretch56 Member

    I thought brake fluid was water soluble and power steering fluid isn't.
  6. Crawdaddy

    Crawdaddy All hail the Mad King!! Staff Member 5+ Years 1000 Posts Platinum Contributor

    What I meant by that is water in brake systems usually means rust and other issues. Whether they mix or stay heterogeneous I don't know. I'd have to look it up, but I think DOT3 and 4 absorb water and cause problems but DOT5 doesn't. Also never mix DOT3/4 with DOT5 or you'll also have rust and other horrible problems happening which will require a complete brake rebuild.
  7. Stretch56

    Stretch56 Member

    Thanks Crawdaddy.

    I guess the technical jargon is "Brake fluid is hygroscopic which means it will attract and hold water molecules" or something like that.
    You're spot on about the DOT 3/4 absorbing moisture and DOT 5 doesn't because it's silicone based.

    I know it just seems weird to use soap & water to clean the plastic reservoir, but a lot of guys in different forums swear by it. Some shops I know, use Metholated Spirits or alcohol to clean them out.
  8. The Heater

    The Heater Rockstar 100 Posts

    I use hot water and soap to clean brake calipers all the time. It's not that it contains water but whether you use the right processes to remove the water. It is not complicated, you just do what I outlined and you are fine.

    Brake fluid is glycol based. Glycol is an exrtremely toxic alcohol. I would never put anything using glycol in my dishwasher. That is insane.

    You can take off that reservoir and clean it in your sink with anything that does not dissolve the plastic. That leaves your choices wide open. Just use the procedure I outlined to make sure all the water is gone.
  9. Stretch56

    Stretch56 Member

    Thanks Heater and I agree about the dishwasher.

    I'll probably wipe it out initially with rags and Q-Tips and then use a toothbrush with hot soapy water. Maybe I'll try throwing some AirSoft pellets into the soapy mixture and agitate it by hand. I'll blow it dry with my air compressor and let it sit overnight before re-installing it. I could use brake cleaner on it if there's anything left.

    - - - Updated - - -

    The Devil is in the details.

    Now that I've committed to cleaning the reservoir, I thought about replacing the two mounting O-rings. But of course, you can't buy those from GM individually, because they only come with a reservoir. I've looked all over, Rock Auto, Nalley GM, Summitt and it's the same. So, I guess it's a crap shoot on whether the O-rings will be ok or not on a 12 year old reservoir.

    Anybody have experience with the failure rates of the reservoir O-rings?

  10. Crawdaddy

    Crawdaddy All hail the Mad King!! Staff Member 5+ Years 1000 Posts Platinum Contributor

    It's worth a try to reuse it, but I'd probably look for a replacement just in case. Knowing my luck, it would be fine in the driveway and fall out a few miles down the road.

    I can't imagine the o-rings are something too exotic. I know there's various types of rubbers like Viton, but I don't know which type of rubber is needed for this application. But, I'd imagine a look through the Grainger catalog would reveal a reasonably-priced o-ring to replace it with.

Share This Page

Newest Gallery Photos