New master cylinder installed

New master cylinder for the CB550F

I finally took a break from everything else (work, fixing the house etc.) and installed the new master cylinder this past weekend. After reading the sohc4.net website blogs I learned that this aftermarket part works wonders - better than the original master cylinder. Since time is precious, I decided to go this route instead of purchasing a master cylinder rebuild kit and repairing the original.


On Saturday morning I got the tools out and removed the original master cylinder. Next I unbolted the brake caliper to remove the brake pads. The previous owner told me he spaced out one day and sprayed WD-40 on the disc and pads, rendering them useless.

The disc pad on the inboard side came off easily, there's a little cotter pin that holds it in position. The caliper side pad was more difficult. The pad was jammed inside with corrosion and grease. I used a hacksaw to cut a groove in the side of the pad and pried it out with a screwdriver. Probably not what a shop manual recommends, but it worked.

The piston inside the caliper looked fresh - I think the prior owner had the caliper rebuilt in recent years. I put in the new brake pads and bolted the caliper back to the front fork.

Next step - routing the brake lines. Problem: The new master cylinder is "shorter" - doesn't stick out as much as the original Honda master cylinder! Result: The brake line was too short by an inch or two. The original line was about a foot long so I needed another line about 14-15 inches in length.

I called Glenn's Cycle Supply and asked if he had any brake lines with banjo fittings. He said no. Then I hopped in the car (I'm not going to ride a Honda with no front brake) and went to Cycle Tech on King Street. The owner, Al was still there (sigh of relief, he usually closes around noon on Saturdays). I asked if he would sell me a used brake line off one of his parts bikes. He said "Sure!"

Al probably has about 20-30 parts bikes sitting altogether on one side of his lot. Armed with my tape measure, I started looking through the bikes and measuring brake lines. I was surprised to see that many of the newer bikes (well, 1990's and up) have one brake line going from the caliper to the master cylinder. Older bikes usually had a junction at the triple tree with a brake line going up and another brake line going down.

I found a Kawasaki Ninja 250 with an upper brake line about 17 inches in length. That's longer than what I needed, but better too long than too short. Al charged me $10 bucks. That sure beats buying a new brake line and this one was in good shape too.

Back home, I routed the brake line from the junction box at the triple tree, up behind the headlight and to the new master cylinder. It was easy to tuck the excess line behind the headlight to make things look good.

Next came the brake bleeding. There are lots of theories about the best way to do it. I just filled up the master cylinder and started pumping on the brake handle, watching the bubbles come up. In time, I put a hose on the caliper nipple and started opening it to let bubbles and old fluid come out as I pumped the brake.

I checked the sohc4 forums for more info on brake bleeding. One suggestion was to tie something around the brake lever and handlebar to keep the brake lever depressed, allowing bubbles to come through the brake line and up into the master cylinder. I did that for several hours and it seemed to help. The brakes work pretty well (way better than they did when I bought the Honda). There's a little sponginess, maybe I'll fix it later. The pads aren't dragging either.

Today I went on my first ride with decent brakes. It was way more enjoyable riding the Honda knowing I could stop with authority when I needed to! I put about 20 miles in, doubling my total mileage since I bought it back in November. The battery had been getting weak too, so I removed the headlight fuse in order to get a quicker charge.

By the end of the ride I was feeling good with a strong front brake, reasonable handling and a recharged battery. Plus I got several stares from people on the street, knowing this Honda has been around for awhile. With gas prices in Honolulu around $3.70 for regular now, I want to do more cruising on the Honda in the future.

If you want to get a master cylinder similar to mine, check e-bay. They usually sell for $80 or so on the auctions. I suggest doing a search for "Yamaha master cylinder" to find the seller, USA-Motorcycles. If you run a search for "Honda master cylinder" it's likely to bring up car parts instead of motorcycle parts. The master cylinders are pretty much the same (whether the auction says Honda, Yamaha, Suzuki or Kawasaki). There are perhaps three different models, just buy one that looks similar to the photo above and you'll be set. Oh, don't forget to get a longer brake hose too!