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Steve Smith

What to use for flushing master cylinder?

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Brake and clutch master cylinders will be removed , paint stripped and housings polished. Old brake fluid looks pretty nasty in them. Don't want to damage internals so what solvent is best to clean them out? Brake clean? Wax & grease remover? Not rebuilding them, just want them flushed out real good.

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I've cleaned mine with simple brake parts cleaner.  A quick spray out then dry with Q-tips to get into all the nooks and crannies still holding gunk.  Let sit a while to ensure it all evaporates out.

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10 hours ago, Steve Smith said:

Brake and clutch master cylinders will be removed , paint stripped and housings polished. Old brake fluid looks pretty nasty in them. Don't want to damage internals so what solvent is best to clean them out? Brake clean? Wax & grease remover? Not rebuilding them, just want them flushed out real good.

 

This will sound crazy, but...clean brake fluid.

 

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I've got one crazier, water.  But I only do it if it's really shitty and can't be disassembled and truly needs to be blasted out.  Using brake fluid is the safest way.  Dump out the old stuff, fill with new, install cap, shake well and pump the piston.  It'll probably clean right up.

 

AFAIKBZITE: Do not listen to Zero.  Brake clean is generally fairly safe for the rubber parts because it generally evaporates very quickly, but if it stays in there, like will likely happen when cleaning an assembled master cylinder, it can damage the seals.  Q-tips can leave lint behind so make sure it's cleaned out well.  If you're taking it all apart then blast away if you want to.

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15 minutes ago, superhawk996 said:

AFAIKBZITE: Do not listen to Zero.  Brake clean is generally fairly safe for the rubber parts because it generally evaporates very quickly, but if it stays in there, like will likely happen when cleaning an assembled master cylinder, it can damage the seals.  Q-tips can leave lint behind so make sure it's cleaned out well.  If you're taking it all apart then blast away if you want to.

 

+1, thought that would be obvious but maybe not.  The only tool I'd consider in there is a soft nylon brush like a toothbrush, and nowhere near seals.

 

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Brake cleaner is fine, but make sure you blow out all the holes and such with compressed air right away for the reasons Oscar mentioned.

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For many years in my shop we used" Denatured Alcohol" as a flush and cleaner, it will not hurt any seals or gaskets, with the Q tips and compressed air this will get the results you need.

Do Not use rubbing alcohol from the drug store it is mostly water, kind of defeats the purpose. 

Dot 3 brake fluid draws moisture, by it nature, so corrosion and rust settle in the lowest parts of the system, so cleaning everything as you described , with Denatured Alcohol, and replacing the brake fluid with a  major name brand "synthetic brake fluid" is the way to go. And by the way, don't forget the Clutch Master Cylinder, it will be nastier than the Brake M/C, think how many times it is used than the brake m/c. 

                                                                 Good Luck

 

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I hadn't thought about alcohol, it should be safe.  And rubbing alcohol would be perfectly fine too, the water in it won't matter since the alcohol needs to be flushed out with brake fluid anyway.

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45 minutes ago, srideaux said:

Do Not use rubbing alcohol from the drug store it is mostly water, kind of defeats the purpose. 

 

FYI, I don't find 70% any more (which still isn't mostly water).  Everything I find on the shelves now is 91%.

 

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If the master cylinder is nasty you're overdue to flush the whole system. I'd draw out as much of the old fluid with a syringe, try to disturb the slug on the botton with the end of the syringe, fill with clean fuid and repeat if necessary then flush the whole system with clean brake fluid. Keep going till the clean fluid is coming out of the bleed nipples.

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Oh and post up pics before and after :)

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ALL of the lines are to be replaced with after market SS ones. Just ordered them yesterday (Galfer). Compressed air isn't a problem as are "Q" tips. I have some alcohol used in auto body work to prep plastic bumper covers. Not sure what % it is, but should work well.

Thanks all for the advice.

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I find whole milk does yeoman's work cleaning braking systems. Drain all the fluid, replace with milk, bleed all the air, cap it up and let it "work" for about a week. Parking the bike outside in the warm sun makes the process work more thoroughly.

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