Brakes
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Joined: Aug 2011
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From: SW Ohio
On another note, DOT 5 changes color as it ages. I've known people who bled old DOT 5 from a system, saw the color wasn't purple and flushed with DOT 4. It wasn't until later they discovered their mistake when the mixture of the two fouled the calipers and master cylinder. If you buy a bike used are are not sure what the brake fluid you took out is, put the old fluid in a container, add a few drops of water swish it around. If it mixes with the fluid it's glycol based DOT 3, 4 or 5.1; if it doesn't mix it's DOT 5.
OP, as to your problem, you have air in the system and it needs to be removed. Many of the things suggested will work but a Mity Vac will be the quickest way to solve it.
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From: San Diego, CA
DOT 5, silicone based, is less dense, leading to the possibility that air can be dissolved into the molecular structure of the DOT 5 without increasing volume. Sometimes referred to as micro-bubbles. This is not the same as trapped air bubbles, that will increase the volume, and be bled out during normal brake bleeding. This dissolved air can be depressed, leading to a "soft" pedal feel. It is for this reason, DOT 5 is not used in ABS, systems, or racing vehicles. (paraphrased from a paper titled, "Silicone Brake Fluid- Joining up the DOT's and Sorting Fact from Fiction", May 2013)
Probably the reason the "zip tie your lever down overnight" trick works... it gives time for the micro bubbles to work out of the fluid, and rise to the brake cylinder...
When bleeding DOT 5 the old fashion way, I never had an issue. When I used my vacuum bleeder, I couldn't get rid of the mushy lever... even though I KNEW all the air was out of the system. I zip tied the lever to the grip overnight, and in the morning I had a solid brake lever...
FWIW.....
Probably the reason the "zip tie your lever down overnight" trick works... it gives time for the micro bubbles to work out of the fluid, and rise to the brake cylinder...
When bleeding DOT 5 the old fashion way, I never had an issue. When I used my vacuum bleeder, I couldn't get rid of the mushy lever... even though I KNEW all the air was out of the system. I zip tied the lever to the grip overnight, and in the morning I had a solid brake lever...
FWIW.....
Last edited by hattitude; May 30, 2018 at 12:53 PM.
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