I'd like to respond to some information I read on this forum and others...

• Some gents try zip-tying the handle to the bar overnight, suggesting it allows the air to flow up into the MC.

My problem with this is, in theory, the cup seal is advanced past the intake hole when the lever is squeezed. With the lever squeezed the only thing that really changes in the system is the reservoir is now isolated from the caliper and line. I'm not tracking on how this is supposed to work.

• I've read several suggestions that say to leave the MC cap off overnight, some with the lever squeezed, some not.

My problem with that is the hydroscopic nature of brake fluid. If I leave the cap off it's going to take moisture out of the air and prematurely ruin the fluid.


Thoughts?

 

Dot 5 turns straw color after a few months of use. Your bike is 5. It takes nothing special to bleed front brake. Do not modify or drill or such. Forget the bleeders and vacuum and such unless your arms are so short they cannot reach the caliper bleeder and the brake lever. Since you are having problem, fill the MC and remove the line at the caliper and drop it in a jar. Pump the lever a few times, if you are not getting plenty of fluid after pumping a few times, my guess is the caliper is improperly built or the line is incorrect. Remove the line and see what you get. If it's still the MC, get you a new slide in complete cartridge from Harley for your single caliper 9/16 or dual caliper 5/8. Once you get a good flow to caliper, simple pump the lever and reach down an break the bleeder with a hose on it in a jar. Let it bled out and when lever gets near bottom, hold it..do not let it back up, and re-snug bleeder. Repeat till you see no bubbles. if that does not work for you, you truly need to pay a good mechanic. If you think you need to modify stock brake components to work, that spells disaster. Sorry to be so blunt, but this is not the place to learn. Vacum type pumps really should not be used on most brake system since the cup type seal is designed to produce extreme pressure one way but a little too much vacuum the other way will draw air into the system. They are OK on a car if you are alone but need to keep vacuum very low.

 

Yes, sometimes they can be a real pain in the neck to bleed. I have a small clear syringe that came with an old Norton master cylinder I bought. Get one of those, fill it with brake fluid, crack the bleeder open at the wheel and force fluid through the little filler hole in the master cylinder (leave the brake lever in the rest position not squeezed). That usually works for me.

I did have one bike that drove me crazy trying to bleed about ten years ago. It was my 87 Softail. I put NEW chrome hand controls on it from Custom Chrome. Did everything that could have been done and I still had no pressure building up. I finally went to Harley and bought a factory master cylinder rebuild kit. Replaced the NEW Custom Chrome cup, o-ring and spring with the genuine HD ones and that's what fixed it.

 

Holding the brake lever in the depressed position forces air to the caliper, not the MC. Same principle as pumping the brakes and holding pressure on it while you open the bleed valve. Allowing it to "sit" overnight lets the system settle but counters airs natural desire to rise back up to the MC.

 

Dot 5 is silicone based and not hygroscopic.

 

Front brake good.

Back bled it with the banjo bolt loose at the MC on Monday afternoon. Zip tied the lever to the bar. Reservoir cap secured, bleeder tight. Let it sit for 48 hours because I couldn't work on it Tuesday.
Went over today and the lever was still mushy. Bungee'd it to the bar and cracked the bleeder. Got some air out of the bleeder. When I released the lever it didn't start to firm up until I pumped it for a minute or so. Noticed a few tiny bubbles come up from the bore of the MC.

Repeat 3x, taking a minute to tap the caliper and up and down the line each time...and voila it's firm, ready to go.


The things I learned about HD brake systems:

• The HD master cylinder bore refills very slowly from the reservoir. I suspect it was in part due to a cup seal that is swollen and needing to be rebuilt. Maybe on different MCs the orifice that allows fluid into the bore is slightly larger. Never in metric bikes or an automobile of any make have I experienced the lag between the return of the piston and the pedal/lever firming up.

• Back bleeding the system from the caliper to the MC with the banjo bolt loose at the MC was instrumental in the success. This eliminated the problem I had with fluid flow in the MC and allowed me to fill the system up to that point nearly air free.

Not sure if zip-tying the lever to the bar helped or not. I don't know enough about fluid dynamics to speak intelligently on the subject, but I do not believe that pressurizing the system causes air bubbles to disobey gravity and flow downward into the caliper. Either way, I did it and now the system works so if and when I have to do it again I'll probably repeat the same process.




Thanks to everybody on this message board for their input, bike would not be on the road again without y'alls help. If only the users of the leading forum for my bike were as knowledgeable and helpful...




Best Regards,
REP