My Dyna's front MC took the rest of its life off and needed replacement. Wasn't fully returning. So I picked up a rebuild kit and some new fancy banjo washers (the new funky ones with rubber in the center) from the dealer and had at it. Sucked out all the fluid (which was clear and pretty since I just flushed about 4 months ago), unbolted the line and wrapped it up in a paper towel and a plastic bag, and kept it completely upright, then pulled off the MC. Old piston out, cleaned the MC with denatured alcohol, blew it out and let it air dry. slathered the lube that comes with the kit all over the new piston and down the bore, and put it back together. Bolted back up, torqued everything and filled the MC with new fluid.

Now here's the tricky part. I read, and was told by a tech buddy of mine, that if I fill the MC and move the lever only about an inch at a time in and out it will fill the piston without pushing air down the line. Do that until no more bubbles rise from the vent holes, then start squeezing a little more. After a bit I should get lever back. I did. I was then told to zip tie the lever about 1/2 way pressed and let it sit for a few hours or overnight, so any air in the top of the line will rise up to the MC. If the lever feels good in the morning, I'm done. If not, repeat and try another overnight.

Has anyone done this? I bought three bottles of Dot4 so if I need to do a full flush and ABS cycle, I can (I have a DT-like device to cycle the actuator) but obviously if I don't need to I'd prefer to save the time and fluid for next scheduled flush.

Any thoughts?

 

I do not know about ABS systems, but it does work non ABS systems.

That has worked with all my bikes.

 

Cool.

ABS Dyna's have a single brake line split off the manifold under the triple which runs back to the control unit. It just releases and applies pressure as needed. In this situation, no air went down the upper line beyond the drop or two that spilled out when I removed the banjo since I held it completely upright while disconnected. So I'm also pretty sure this will work fine.

One question though, I have the bike on a scissor jack holding it upright. Wondering if I should lower it on to the jiffy stand so the MC is at more of an angle (even higher then the banjo bolt) instead of parallel with the deck. Probably doesn't matter at this point. I already have pretty good lever feel after about 4 hours.

 

I don't think it matters if it's upright or not.

More power to you on the rebuild. I have tried them so many times and I always screw it up. That's one thing I always let a shop do. I take the master cylinder off and drop it off to them. I hate doing them.

 

It was really simple actually. Literally minutes. A small flathead to pull off the seal, pliers to pull out the piston. Hosed down the MC with alcohol, wiped out the piston bore, blew it out with air and let it sit to air dry (that took the longest). Reassembly as said was 30 seconds. Can’t see how one could mess that up. Only thing was to use the rounded end of a small ball end hex wrench to press the new seal back in place. Pops right into its channel. Can’t screw it up. Then just reassemble and fill. Easier than changing oil. Seriously. Give it a try next time. The “anti-gravity” bleeding seems to have worked as I have good lever pull as of this morning. Pretty much the same as my Road King so I’ll go for a mild test ride later and call it a day.

 

Same, rebuilding my front master cylinder was one of the easier things I've done on my bike. I flushed the rest of the fluid at the same time that part took the longest. Actually probably due another brake fluid flush now that I think of it.

 

Agreed! I hate pretty much anything having to do with brake fluid.

 

I agree on that. Feels like handling nitroglycerin back in the old westerns. One wrong move and....

 

Yep actually I don't even go 1".... I usually just tap the lever just enough to lightly compress and watch till the bubbles stop rising...

 

In order for the zip tie method to work properly the small holes in the bottom of the reservoir need to be the highest point in the system. The larger of the holes supplies brake fluid to the system, the smaller hole is the return port and is generally where you will see the last remnants of air bubbles coming from when bleeding the master cylinder. Typically on the jiffy stand with the handlebars turned left. The other option you have is to bench bleed the master cylinder before installing it back onto the handlebar.