DOT5 Silicone Brake Fluid
by Mike Cecchini Jan. 2022
First, what you need to know & be aware of.
What most people fail to understand is DOT3 & DOT4 brake fluids are hygroscopic, meaning they absorb and hold moisture.
This is why DOT3 & DOT4 brake fluids need to be changed and flushed out every 2--3 years so the moisture will not attack the bare steel brake parts like caliper & master cylinder pistons, caliper & master cylinder walls.
DOT5 brake fluid is NON-hygroscopic, meaning it does not and will not allow moisture, condensation or water to enter the brake system as long as the brake system is completely full of DOT5 silicone brake fluid. If someone tells you that DOT5 brake fluid causes moisture to puddle in the lowest parts of the brake system and this water causes corrosion issues, this simply means that brake system was NOT completely disassembled and cleaned of ALL previous brake fluid. Sloppy & poor work habits they blame on DOT5.
This is why use of DOT 3 and DOT 4 moisture contamination is THE leading cause of brake issues and the need to rebuild brakes, especially those in vehicles that sit around a lot not being used..... ie....most vintage bikes and cars.
I have been testing and using DOT5 brake fluid since 1985 when Dow Corning put it on the market. I have installed it in many NON-ABS Japanese, European and American cars and motorcycles with 100% success. Zero issues. This includes Brembo, ATE, Bosh, AP Racing and many more. Follow the directions below to the letter so you can reap the rewards of this great brake fluid......especially when vintage brake rebuild kits are no longer available. Then what do you do? I have a solution for this, but this will be another article.
DOT3 & DOT4 brake fluid can easily harm paint, rubber & wiring if spilled on these items....and must be (at least) flushed with copious amounts of water to neutralize it.
DOT5 silicone brake fluid will NOT harm paint, rubber, wiring or just about anything else when spilled on these items. Even if you get it on your hands, simply wipe it off. No problems or issues.
DOT5 silicone brake fluid is NOT for racing applications as it turns into a poor lubricant at temps above 750F degrees and does not allow the caliper piston seals to retract the pistons, so the brake pads will over-heat and not work properly. I tested DOT5 on the race track when I was doing track events with my Ducati's. I ran in the top level group and my calipers never went above 400 F, so for the non-professional rider DOT5 will work fine, but do monitor your caliper temps to be sure you do not go over 700F degrees. There is crayon type of paint sticks that discolor when a particular temp is reached. Cheap & easy way to know how hot your brakes get.
DOT 5 Brake Fluid Installation for Brake Systems that have been exposed to DOT3 & DOT4 brake fluids.
(If you have a VIRGIN brake system that has NEVER had DOT3 or DOT brake fluid in it.....then just put the DOT5 in and bleed the system to firm lever or brake pedal.)
The proper and 20+ year proven way to install DOT 5 into any non-ABS brake system......car or motorcycle.
1. Remove the calipers and master cylinder(s) and take them completely & totally apart.
2. Remove all the caliper & master cylinder rubber seals. Wash them in hot soapy water, rinse in hot clean water, blow dry with low pressure air to ensure every bit of moisture is gone 100%. . Flush with denatured Alcohol to ensure any residue of any kind is removed. Anything less than 100% is unacceptable. Take your time. This is where 99% fail to do the job completely. Simply using some spray 'Brake Clean' is not enough.
3. Remove all braided & plain rubber brake lines with new VIRGIN brake lines. Flush the brake lines with denatured alcohol you can buy at most hardware stores.
4. Using the silicone grease that comes in most brake rebuild kits these days, LIGHTLY coat all the rubber parts (seals & 'O' rings) and any parts they come into contact with. If you didn't get the silicone grease in your kit, simply use a light coating of DOT5 brake fluid to assemble everything.
5. Assemble the caliper/master cylinder(s). Put the master cylinder and caliper(s) back on the bike. Hook up the brake lines and put some DOT 5 brake fluid in the master cylinder. (Btw.....no worries about spilling DOT5 brake fluid on anything. It is 100% totally harmless to all paint, wiring & rubber.....and your hands. Just wipe it off with a clean tissue.) Bleed the brake system per the shop manual....or whatever works for you.
6. If the brake system will not bleed to where you have a firm lever pressure (quite normal), put the bike on the side stand and turn the handlebars full lock LEFT (so the master cylinder is the top point of the brake system). Put a rubber band from the brake lever to the handlebar so the lever is pulled back as far as it will go just like normal hand pressure will do. Leave it overnight. This will allow most (all?) of the air bubbles in the brakes rise all the way up into the master cylinder and eventually into the master cylinder brake fluid reservoir where you normally will see them as you pull the brake lever in/out/in/out. You can see it happen if you have the top off the reservoir.
7. Next day try bleeding the brakes again without moving the handlebars or the bike. You might have to do this 2--3 times to get the brake lever back to "normal" feel.....which should be fairly firm or better.