Two and a half decades is a long time. It also happens to be the same amount of time since the brakes on my old 1994 Honda CBR900RR were last touched. I figured it would be a good idea to refresh the inner-workings of one of the brake system’s most critical components: the brake calipers.
The process of rebuilding brake calipers might seem daunting, but it’s really not that bad. Let’s see what it takes!
(Note: Before taking a project like this on, be sure you have a good understanding of how your vehicle’s brake system operates. If you have any doubts at all, please take your vehicle to a professional mechanic to have the work performed.)
The Tear Down
Before I could start disassembling the brake system, I needed to remove as much brake fluid from the system as possible. I grabbed a turkey baster and began drawing out the brake fluid that was in the master cylinder reservoir and placed it into a spare container. I made sure to not drip any brake fluid on painted surfaces or on my skin—it’s toxic stuff.
With much of the fluid now removed from the system, it was then time to head on down to the brake caliper and begin work from that end. I first cracked open the brake line banjo bolt that feeds into the caliper. I did this with the caliper still on the bike because the banjo bolt is often very tight, and if the caliper isn’t held in a fixed position, I’d have a difficult time freeing the bolt. I left the banjo bolt screwed in all the way because I didn’t want the residual brake fluid in the lines to come pouring out yet.
Following this, I unbolted the caliper from the fork leg and peeled it away from the brake disc. Next, I removed the brake pads and their related components from the caliper body.
With the caliper in hand, I began unscrewing the banjo bolt all the way. I placed a drip pan underneath the caliper to catch the ensuing downpour of brake fluid flowing from the brake lines. Once the line was cleared of fluid, I turned the caliper upside down over the drip pan to drain the remaining fluid from the caliper.
Even this early on in the tear down process I could tell I would be met with some fierce corrosion going forward—just take a look at the inside of the banjo bolt!
The caliper I’m demonstrating with utilizes a two-piece body. The next stage of the strip down consists of unscrewing the bolts that tie the two halves of the caliper together.
With the bolts removed, I pulled the caliper halves apart. One of the caliper sides, for the lack of a better term, is the “master” side where the brake line attaches to and brake fluid enters. The fluid is transported from the master caliper side to the other caliper side via two small bridges at the top and bottom of the caliper. It is critical that these bridges remain clear of debris so that brake fluid can pass through freely to actuate the caliper pistons on both sides of the caliper.
I was shocked when I found out how clogged the bridges were on this caliper. Congelation such as this shows why it is so important to change your brake fluid often. It’s no wonder why the brakes on this bike felt mushy - with this much build up in the bridges present, only half the pistons in the caliper would have been actuating correctly.
The next step of the caliper tear down is where things get really messy: removing the pistons from the caliper bores. There are a number of methods out there for extracting caliper pistons, but the easiest method I’ve found is by employing compressed air.
I directed compressed air through the fluid bridges to “pop” the pistons out of the caliper bores. You’ll want to be gentle with your application of compressed air; too much air will cause the piston to shoot out like a bullet from the bore. Definitely wear eye protection during this stage.
Also, keep the caliper bores pointed towards something that can trap the rapidly escaping piston. Cover anything around you that could be damaged by brake fluid (i.e. your skin and painted surfaces) as there will undoubtedly be brake fluid splashing around during this.
With the pistons extracted, the true condition of the caliper’s internals could finally be seen. Yikes! That orange, rust-like sludge is what you can expect to find if your brakes haven’t been touched in many years. That sludge will greatly impact braking performance and eventually cause the pistons to seize in the bores, ultimately leading to brake failure. Not good.
With shop towels and a few cans of brake parts cleaner at the ready, I went to town cleaning the calipers and pistons. After a laborious 15 minutes, all the parts cleaned up nicely. I was relieved to find that there was no pitting present on the pistons or in the caliper bores. If there had been, replacement of those components would probably have been necessary.
With all the orange gunk removed, it was time to remove the old piston seals and dust seals that were present inside of the caliper bores. It’s critical that you don’t scratch the caliper bores when extracting these seals. You’ll want to use a tool that is softer than the caliper’s metal. I found that a zip tie works great for this job.
With the old seals removed, it was time to install some new ones. I managed to find a complete caliper rebuild kit on eBay for only $30. The kit came with new seals, new caliper pins, and new copper crush washers for the brake line banjo bolts. So, in other words, everything I needed in order to properly do the rebuild.
The new seals slotted into the caliper bore grooves leaving a refreshed appearance in their wake.
Next, I went to press the cleaned brake pistons back into the caliper. Before doing anything, I applied a light coat of fresh brake fluid to the outer surface of the pistons. This would allow the pistons to slide past the seals without getting hung up.
You want to be gentle when installing the pistons and ensure that you’re pushing them in as straight as possible. There is potential for damaging the new seals if the pistons are installed haphazardly, which could lead to brake fluid leaking past the piston seals.
Now that the pistons were seated in the caliper bores, it was time to fit up new bridge seals and then bolt the caliper halves back together.
With the caliper bolts tightened to specification, I went ahead and “reloaded” the caliper with brake pads, pad springs, and anti-rattle shims while it was still off the bike.
The caliper could then be reunited with the forks and then the mounting bolts torqued to specification. Next came the installation of the brake line. I offered up new copper crush washers on either side of the brake line fitting and snugged down the banjo bolt to the correct torque specification.
Since I had completely drained the brake system of fluid, it was now time to fill it back up and bleed out the air. I won’t dive into the details of how to bleed a brake system, but good tutorials on this process can be found with a quick Google search. I discovered that a method called “reverse bleeding” works great for this job. This method will have you pressing brake fluid from the caliper up to the master cylinder, which results in all the air being pushed out through the brake fluid reservoir.
Bleeding the brakes may take some patience, but eventually you will be left with a firm brake lever, a completely refreshed brake system, and a renewed confidence in your vehicle’s stopping abilities.
Stopping On A Dime
While rebuilding brake calipers might not be the best place for a new wrencher to start, the process certainly isn’t as much of an undertaking as it might first appear. Even if you’ve worked with brakes before, I’d still recommend giving yourself the better part of a day to complete the job start-to-finish. You will probably make a mess, there will be some head scratching, but with perseverance you’ll see the light at the end of the tunnel.
For well under $60, you can give your old machine the braking performance it once had all those decades ago. For my classic CBR, the run of neglect was over and the brakes have never been better. What a result!