I have an '09 Ultra Classic that has recently developed a brake fade problem with the rear brake. It occurs when stopping slowly over a long distance, such as when approaching a red light, or, in other words, any situation where you might "feather" the brake. When I first apply the brake, I have full braking power. If I let off slightly, then re-apply, the pedal goes a little farther down. As I repeat that action, the pedal eventually bottoms out and I have no braking power. If I fully release the brake and re-apply, the braking power returns. When it started happening, the two causes I could think of were worn brake pads and air in the brake line. I checked the pads and they have plenty of life left on them. So, I used a vacuum bleeder to fully flush the system and get fresh fluid into the brake line and remove any air bubbles. It didn't help. I was hoping that someone here who has more knowledge of hydraulic brake systems than I do might offer a clue about what could be going on. Thanks!

 

It sounds like your rear brake master cylinder is blowing pressure around the plunger and needs rebuilt.

 

Exactly!

 

Along with a bad master cylinder (had an '88 Vette with the exact same issue) I also thought that there was a special tool needed to bleed brakes on our bikes...or is it only for ABS equipped bikes. Am I wrong?

 

Thanks for the info! I was just looking at HD part number 42932-08A - Rear master cylinder rebuild kit. For about $30, that seems like the way to go. These are non-ABS brakes, so no special tools needed.

 

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How many miles are on the bike?

Has there been any brake fluid missing and or leaking from the rear master cyl recently showing rear caliper, rear master cyl or rear brake line has an issue?

But from what you said thus far it seems like an issue with rear master cyl and or bake line thats gone bad expanding and or ballooning as more brake pressure is applied coming to a stop.

scott

 

I thought I would post a follow-up to this in case anyone has the same issue and finds this thread while looking for answers. I installed the master cylinder rebuild kit 42932-08A that I mentioned above and that solved the problem. I now have good, solid rear braking power with no fade. So, thanks to Scrmnvtwins and Boomer1143 for pointing me in the right direction. If you're planning to try the same fix, please keep reading.


The rebuild kit comes with a new piston, primary and secondary seals, primary seal washer, piston spring, and the e-clip that holds the spring in place. In fact, all of that comes already assembled. It also includes a new retaining ring for securing the piston in the master cylinder, but the ring was too small for my application (it must be for a newer version of the master cylinder), so I ended up using my existing retaining ring. I would recommend having a service manual handy when doing this project, because the master cylinder has to be removed from the bike to do the rebuild. Here are a couple of helpful hints:


- To remove the master cylinder, you have to remove the right lower faring, right rider's floorboard, and the brake pedal, and you have to disconnect the brake line from the master cylinder by removing the banjo bolt. Because you're removing all those items, you're going to need to replace some things when reinstalling them, if you want to do it "by the book". You'll need two new copper washers when you reinstall the banjo bolt (I went ahead and replaced the bolt, too). You'll also need two new o-rings and a new locknut when you reinstall the brake pedal. My local H-D dealership had all of those items in stock, except the o-rings, but it turns out they're just standard #12 o-rings that I was able to pick up on the plumbing aisle at Lowe's.


- When installing the retaining ring that holds the piston in place, you might want an extra pair of hands. I was able to use the pushrod to push down on the piston and compress the spring with one hand and install the retaining ring with with the other hand, but it took three or four tries. It would have been easier to have someone else compress the spring while I installed the retaining ring. However, when installing the e-clip that holds the pedal return spring in place, you're definitely going to need some help. The manual says to use a suitable spring compressor, but my tool collection isn't extensive enough to have anything like that, so I had to be the spring compressor while my son pushed the e-clip into place.


I hope this is helpful to anyone doing the same rebuild. Feel free to shoot me a PM if you have any questions.

 

Good info indeed, OP...thanks for circling back! One ironclad rule passed down to me by my dad was to never rebuild a master cylinder...only buy new...but on our bikes with two separate systems, I think that's an exception to the rule! The way you went is certainly cheaper than buying new...and gets the job done!