I have known for some time that you are supposed to change your brake fluid every once in a while, but I admit that I have been slack in that area lately. Recently, I had to break open a brake line on my caliper and then bleed the air out of the line. Imagine my surprise when try as I may my brake caliper wouldn't pump up. I must have pumped that brake lever for 45 minutes. So I went in defeated, and went to the Interweb and read, and watched a few videos. There is a recommended interval to change your brake fluid, and I was way beyond it. Moisture can somehow get into your line, and ruin the hydraulic properties. One fellow had some sort of measuring device, and compared his brake fluid to new brake fluid. The old fluid was indeed contaminated.

Now back to my problem of bleeding. I learned of a method of "reverse" bleeding calipers that wont respond to brake lever action. You fill a large brake fluid pump or large plastic syringe fitted with a piece of rubber hose over the bleed screw, and flush backwards with the brake fluid reservoir open. The idea being that al the air in the caliper would be pushed all the way up through the line, and you would have brand new brake fluid through out your system. I performed this task flawlessly. Do it slowly, or your open reservoir will become a 10-15 foot geyser! It's really fool proof. But to my amazement, after all the air was purged out of the line, my brake caliper still wouldn't pump up! Defeated again? Time to start diagnosing by the method of "most likely" and "the cheapest" part. A method I learned in High school auto shop. Mr. Reagan taught me that the most likely culprit in any mechanical diagnosis is usually the cheapest part in the system. So with that knowledge, I went to the tool box...Old brake fluid-Caliper seal kit-reservoir rebuild kit-Caliper Piston-Caliper-That's the order of thought in that diagnosis.

I have to assume that moisture was beginning to do what moisture does in a brake system. A quick tear down of the caliper revealed a "stuck" piston. It wasn't real stuck, but it took a good amount of air pressure to release the piston from it's locked state. The caliper bore wasn't damaged, and neither was the piston. The seal was stuck to the caliper wall after I removed the piston. It was about this time that I realized that I didn't have the parts to rebuild the caliper. A phone call to Harley-Davidson parts counter revealed that none were in stock. (older Evo) A few phone calls later to any V-Twin shop within 50-75 miles revealed that it would have to be ordered. This wasn't going to be finished any time soon. I ended up ordering a kit on eBay, and had to wait.

I am told that HD brake fluid is conventional material (mineral) and Dot 4. So I gathered some Dot 5 brake fluid over the next couple of days. I live in a small town, so Dot 5 is not sold everywhere, but can be ordered by most. Dot 5 is synthetic and surpasses all brake fluid tests above the Dot 4 standard. It is more resistant to high heat and moisture as I understand it, and is a very good thing for motorcycles. I also learned that there were quick bleed caliper bleed screws with a one way valve inside them. You loosen them and they don't let air in, just fluid out. 15 bucks for two chrome ones. Great for do it yourselfers. They wont allow the reverse method of bleeding though. Keep your regular bleed screws for that.

Less than a week later, and the caliper was reassembled, and installed. There was now a large growing brake fluid stain on my garage floor. I ended up draining the reservoir with a syringe, and reverse bleeding the system since the caliper was empty now, and had synthetic dot 5 fluid all throughout. To no ones surprise, my brake caliper pumped up in about 10-15 pumps. Voila!
I am now back in the corral of MC owners who regularly change their brake fluid. I don't know what the moisture content was due to the fact that I don't have a measuring device. But the used brake fluid was dark in color and looked like dirty oil. (Oxidation?) Synthetic Dot 5 is purple in color, and see thru.

The moral of the story here...I knew about brake fluid preventative maintenance. I take comfort in the PM of my MC's as preventative of further breakdown. For some reason, I became complacent, and let this one slip past me. It's something I didn't really have in the forefront of my mind, and I got burned. I am now officially back to "Righteousness" in the brake fluid maintenance corral...

 

Are you using DOT 5 OR 5.1? You may want to read this; https://www.epicbleedsolutions.com/r...1-brake-fluid/

 

DOT 5 is not compatible with an ABS system ... DOT 5 will aerate under ABS cycles ... I didn't see where you mentioned what year, make and model you were working on ??

 

Hi...and thanks for posting. I did come across 5.1 brake fluid when I was shopping. The stores didn't and couldn't explain the difference, and the cost was quite prohibitive. One casher told me it might have something to do with ABS systems. Now that I have read the info on your link, I realize how important that is.
Thanks again for the link....I'm going to print that out, and save it!

 

Older Evo...no ABS. I didn't know that about Dot 5 fluid and aerating in ABS...Thanks!

 

Add a signature line on your bike year and all letters.

 

I will, and I have been meaning to...I'm trying to get decent photos of my bikes as well. I'm a terrible photographer...lol! In my defense, I did say in my OP that I was working on an older Evo though. MY bikes are listed in my profile for now.

 

Dot 5 is the Harley recommended fluid in older evo bikes.

 

Holy long story Batman

 

Maybe...I have some older factory MOCO brake fluid and the color is the same as Dot 4. DOT 5 has always had that Purple color. And somewhere long ago, I read, and was under the impression that HD brake fluid was Dot 3 &4. the bottle doesn't say what it is, so I must have read that somewhere. Kind of like Harley fork fluid doesn't give the SAE specs. Just calls it type "E" fluid. Every Jap bike, I ever owned used Dot 5 as I recall. Makes sense to recommend it.