Recommendations On Flushing Brake Lines

[Daniel K.]

Re: Recommendations On Flushing Brake Lines

OK, thanks everyone for responding to my request. Looks like I'll stick with steel lines and continue on with the DOT3 for the next couple of seasons. I'll squirt some Brake Clean in the lines and suck it out with my vacuum bleeder.....which sucks.....I mean, does not work as well as I expected, but for this application, should be go to go and I'll see what comes out of the system. If this approach is inadvisable, please let me know. Thanks again for your interest in my project.

[Louis T.]

Re: Recommendations On Flushing Brake Lines

Hi Daniel,

Given that you're sticking with DOT 3 or 4 (before and after), there's no contamination to attempt to flush out with Brake Clean, and if there was, squirting the stuff in one side and trying to extract it via suction from the other end would be an exercise in futility. It's one thing if you buy the stuff in bulk in non-aerosol form and run it through the lines (metal lines only - never through components composed of or containing rubber) as you would brake fluid. Squirting the stuff through a can leaves air in the lines and Brake Clean evaporates very quickly, and though it leaves no residue, would leave some of whatever contamination you were theoretically trying to eradicate. Spray cans of Brake Clean were simply not designed for this purpose.

Glycol-based brake fluids like DOT 3 and 4 degrade more from water absorption than anything else. (It is this hydroscopic property that causes many classic car owners to switch to DOT 5 - silicone.) Dirt or dust really aren’t the issue, and if they were, a simple fluid replacement through an extended brake bleeding would take care of it (if you search the archives, you'll find John Hinckley discussing a Motive pressure bleeder that he uses that would make this task easier and quicker).

By the way, if you're concerned about possible corrosion in the lines, the Brake Clean isn't going to do the trick anyway, so if you really suspect rust, bite the bullet and change the lines now, before you put those nice new components at risk.

Bottom line: air and moisture are your enemies. The more fresh fluid you flush through the system, the greater your success in eradicating these.

Good luck!

Louis

A final note - fresh fluid means new fluid in new bottles. Don't use any half-full bottles sitting in your garage for years, as they may have already absorbed moisture. That's why most will recommend small containers for topping off or routine (minor) brake bleeding, and big bottles only when you're doing a complete fluid replacement. This way, bottles get discarded soon after use.

[Duke W.]

Re: Recommendations On Flushing Brake Lines

I'm not sure what Brake-Clean is, but the flushing fluid must be a non-petroleum product that will completely evaporate and not leave any trace of residue. Denatured alcohol is what I recommend.

Thorough drying with compressed air is also required. Once the liquid has been blown out, a Mighty Vac can be used to draw a vacuum on the pipes, which will help remove any remaining amount.

With the system completely down for rebuilding, now is a good time to switch to silicone fluid, but you will have to disassemble new or rebuilt master and wheel cylinders, clean them with denatured alcohol and reassemble them with silicone fluid. Also thoroughly flush new brake hoses with denatured alcohol.

Duke

[Daniel K.]

Re: Recommendations On Flushing Brake Lines

Louis,

Thank you for taking the time to respond. I appreciate your sage advice and will use DOT 3 to flush the system.

Again, thank you for your help.

[Tom R.]

Re: Recommendations On Flushing Brake Lines

When using silicone (Dot 5), you may wish to avoid "power bleeding" methods since they agiate the fluid and induce air into the brake lines, contributing to a soft pedal and requiring more time to bleed.

Others may have developed a technique that softens the use of tools such as the Mity Vac...I used the drip method. I believe this is discussed in previous methods.

Also J Hinckley wrote a nice article on Silicone in last month's edition (actually September) of Corvette Enthusiast...which may still be on the news stands.