Honda CB 550 Front Brake Overhaul

The right size, or not?

For the past few months I have been slowly gathering the parts to do a complete overhaul on my front brake. Compared to modern bikes, my old 1976 Honda CB 550 K does not have the best braking power, so I figured making it as good as possible, was the responsible thing to do.

I love my bike, I really do. I love the look of it, I love the history that I imagine for it, over it’s 35 year lifespan. But we ride in NYC, and that often requires some serious stopping power. Great stopping power is something this bike doesn’t have. Don’t get me wrong, I have been able to navigate the traffic of this city just fine. But there is always the thought in the back of your mind, that eventually that inattentive driver will pull in front of you without notice, even though you have the right of way.

When I first got the bike, I immediately did an overhaul on the front brake Caliper. I installed a new piston seal and brake pads, hoping it would improve the system a bit. I think that it did, but I have very little to compare it with.

One thing that came up many times, while researching fixes for this bike, was that steel braided brake lines would offer a noticeable improvement. The “flex” that occurs in rubber hoses, when the brakes are applied, lessens the effectiveness of getting fluid to the caliper, therefore slowing the rate at which the piston activates the pads. This all made sense, so I knew it was a fix that I wanted for this bike.

There is a guy on the SOHC-4 forum who makes custom steel hoses, and even has special discounting for forum members. So I finally ordered a set, specific for my new, lower drag bars. If you have lower bars than stock, the stock brake hose length is too long, requiring twists and turns, that you neither want nor need. Getting new, shorter length hoses also helps proper delivery of the fluid, so I felt like I was headed in the right direction.

The other thing I wanted to replace was the brake Master Cylinder (MC). The one that came on the bike was clearly not stock (was for a mid-80’s dual disc set-up), and although most people consider more modern MCs to be superior, I was not confident the Previous Owner (PO) had chosen the proper MC for this bike. Based on other “fixes” he had done, the chance was slim that this was worth keeping. So I bought a used stock CB 550 MC, and the rebuild kit to freshen up the innards.

I had been accumulating these parts for about 3 months, and finally decided to get down to it. The first thing to keep in mind, when dealing with Brake Fluid, is to wear rubber gloves. Apparently, brake fluid is very toxic, and it seeps right through your skin to your liver. So wear gloves!

As a first step, I had rebuilt the Master Cylinder, despite some problems getting the damn thing apart. The old one I bought was seized, meaning the piston inside would not move, even after soaking it in every fluid I could find. You need this piston to move down into the bore, so that you can get a small, evil circlip out. Turned out I needed to order a special set of circlip pliers (snap ring pliers) with thinner arms, to fit down into the bore. Finally got it all out, and replaced all the innards with the help of this video.

Then it was time to tear the whole brake system down. Although I have the garage space now, I find myself still exhibiting a NYC curbside mechanic mentality. I never take on fixes that I can’t finish that day, so that the bike can get put back together, and I can ride home. Some future fixes are going to put an end to that real quick. Taking the front end apart, polishing and rebuilding, will NOT be done in a single day. That’s where MotoPreserve comes in!

I first drained the entire system of brake fluid (made a mess, but was wearing gloves!). Then I removed the caliper from the front forks, unhooked the two brake hoses, and removed the old MC. I was on my way.

I took apart the caliper while I had it off, and scraped some of the old paint off it. I didn’t take the time to polish it – for fear it would take too long. Another part I had squirreled away was a custom-made caliper piston, also made by one of the SOHC-4 forum members. These are phenolic, and will not pit like the stock metal ones. My original was severely pitted, even after wet sanding it as best I could. So this offered to be an improvement over my current set-up as well. Caliper clean, time to get the hoses run.

I got the hoses on without much effort. The strange “banjo” bolts have some angles to them, so getting them lined up correctly took some finagling, especially with the tighter work space, due to the lower drag bars. Not too much hassle though, and I left them loose so that I could wiggle them later, if need be.

Next was installing the MC on the bars. I have polished this thing on the buffing wheel, and it looked almost chrome. Better looking, and I hoped more correct for this bike. Problem was, with the lower bars, the MC was too tight to the top of the forks – hitting the fork tube caps. UGH! After messing with it a bit, I realized that no matter what I tried, the angle at which it sat, was never going to be the same as the angle the clutch lever sits at. It will have to do for now.

After getting everything installed on the bike, next comes the frustrating process of filling the bone-dry system with fluid, and then bleeding the brake lines. Bleeding alone can be annoying, but when the system is flushed completely, or is brand new, the process becomes more of a pain in the ass. You need to get the fluid flowing to the caliper first, and then begin the proper bleeding procedure.

Freshly polished Master Cylinder

I don’t have a speed bleeder, which prevents the need to open and close the bleeder screw every time you pull the lever, to remove the bubbles from the line. Getting all the bubbles out is the goal here, and it can be time-consuming. Especially, if like me, you wailed away on the lever, trying to get the fluid to flow, while initially priming the line. Bad move! I ended up spending an hour bleeding the system, and in the end, appeared to get all the bubbles out. Problem was, the lever still seemed soft (or spongy).

Turns out, I may have received the wrong length MC piston. Apparently, there are 2 sizes, and although I ordered the rebuild kit specific to my bike, others have had this problem. So I will head back to the garage (and another set of gloves!) and attempt to re-bleed the line. Hopefully, the piston is correct, and I just need some more bleeding to get the lever-action hard, and correct.

Wish me luck….


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