Flushing Glycol From The Brake System

[Patrick T.]

I plan to flush the glycol brake fluid soon from the entire system of my '67 and replace it with DOT 5 silicone brake fluid, as I've always had a preference for silicone, which worked very well in my previous frame off '57 project, but that was a new SS system. I plan to install new SS brake lines this winter, but for now, I just want to purge the old lines and put the DOT 5 in. No matter how carefull I am, somehow glycol always seems to drip on my newly detailed components, eating the paint and I've had it up to here...

I know you HAVE to get all the glycol out, but the problem is flushing the laminar coat which clings to the inside walls of the master cylinder and the brake lines. I figure I'll need 1 quart of sacrifical silicone to flush and 2 more quarts to fill the system. Should I just open the bleeder valves on all of the calipers and just blast the glycol out, or just do one at a time ? Are there any flushing agents available which could be used to strip the lines of glycol before filling with silicone? Or should I just wait until I replace the lines with SS? Any advice would be appreciated.

[Rob Brainard]

Re: Flushing Glycol From The Brake System

Patrick, I would wait until you replace the lines. However, the problem is not with the lines, but with the calipers and master. You really need to disassemble them in order to get all the "old stuff" out. If you MUST do this before hand, flush the system with "DENATURED" alcohol. This will get the glycol out of the master [hopefully all of it] and the lines. I assume you like DOT 5 because it does not hold moisture, but remember the calipers are the weak link in the system and they will hold some of the glycol unless you disassemble and clean them.

[Jerry Clark]

Re: Flushing Glycol From The Brake System

Hi Patrick:

Rob is correct and in the optimal situation I would opt for a completely clean system, however, the new DOT 5 silicones, (not all), are Glycol compatible, of the ones that are, NONE recommend mixing the two fluids, but they are more tolerant of the Glycol residue.

Several of the cars in the collection have been "converted", i. e. switched to DOT5 without totally replacing / cleaning all components with great success. Only one, ( 65, 365 ) had a problem and that was traced to a burr in the brake master which worked perfectly with Glycol but hung up with DOT5. It is generally believed that the Glycol has a better lubricating profile that silicone and problems that were not apparent in Glycol systems can make themselves known in silicone. Other than this one example all the others functioned perfectly. How they hold up over time has yet to be seen but the master shown no signs of contamination.

Best of Luck.

jerry

[dale pearman]

Re: Flushing Glycol From The Brake System

Am I missing something here? I thought gycol had an affinity to water, Whats wrong fith a water flush after removing the calipers. Also, why stainless brake lines? GM didn't use them. I wonder if expansion and contraction and stainless' infamous inelasticity had anything to do with it? Aside from the spills, why on earth use silicone brake fluid? Going racing at Sebring or Daytona?

Youre gonna get condensation in the brake lines regardless. Would you rather have that water be absorbed by DOT-3 or have pockets of water in the lines acting aginst the silicone? Some folks love DOT-5 but not if they bleed at sea level and then go into serious altitude. Oops! NO BRAKES! I will concede that the boiling point of silicone is higher which is desirable for racing but face facts. How many grocery getters have you heard of with brake failure from boiling away the fluid on the street? Not very many, with the possible exception of my Aunt Tillie. She pulls negative "g"s on the way to the Senior Citizen Center.

I cast my vote for steel TBW (tube bundy weld) brake lines, DOT-3 fluid, and a steady hand wheen fooling with the stuff.

!mooooooooooooooooooooooraV

[Duke W.]

Re: Flushing Glycol From The Brake System

I have never heard of anyone successfully flushing glycol fluid with silicone. The two liquids are not miscible and have different specific gravity and viscosity. I don't think you can ever get all the glycol out by flushing with silicone, so whatever moisture is left in the remaining glycol will have a field day corroding your system. Stick with the glycol for now and flush it every two or three years with a quart of fresh fluid. You can keep a spray bottle handly to spritz off the calipers if any fluid oozes out the threads, and pack a damp towel under the M/S to catch any spillage. (Glycol is water soluble.) Also, replace the cover without hooking the bail wires, which will minimize spillage. As you probably know the first eight inch or so of main piston travel causes a "little old faithful" geyser of fluid until the compensating port ports are covered by the cups.

To convert to silicone you should disassemble the calipers and M/S, thoroughly clean them with denatured alcohol, then assemble everything with a film of the silicone fluid. Flush out the lines with alcohol and then thoroughly dry them with compressed air.

Duke

[Terry M.]

Re: Flushing Glycol From The Brake System

Dale,

How is the water to get in the brake system once DOT 5 is installed?

Terry

[Scott Marzahl]

Re: Flushing Glycol From The Brake System

When I used to slalom race with the Guldstrand club, I switched to silicon fluid. I purchased two quarts from Vette Brakes and used one to flush with and the other to fill it up. Ran the card hard for about five years and never had a problem. Scott Marzahl

[dale pearman]

Re: Flushing Glycol From The Brake System

Terry: Same way it gets in with DOT-3. Condensation!

Dale.

[Terry M.]

Re: Water inThe Brake System

Dale,

I have been laboring under the impression (boy is that hard work, too) that the water that enters a DOT 3 or 4 system gets in because that fluid likes and absorbs moisture. I figured it entered through the breather vents in the master cylinder top (although this should be minimal if the rubber diaphragm in the master cylinder cover is properly installed and functioning) and by hygroscopic absorption through the flexible brake lines.

I was taught the rubber in the system is not completely impervious to water on a molecular level and that is where the water comes from.

My belief is that since DOT 5 is not hygroscopic absorption through the flexible lines does not take place, nor does moisture enter through the master cylinder given proper diaphragm operation.

If there are no air pockets in either system, I fail to comprehend where the condensation takes place. Any air pockets would give a mushy peddle in either case, so my belief is that neither system would function well with air pockets. In what part of the system does the condensation take place?

Terry