CB550K update - front brake caliper rebuild

Today I managed to find time to tear apart and rebuild the front brake caliper on the 1977 CB550K that I'm presently restoring.

The piston and pad would move out and apply pressure to the brake disc, but wouldn't necessarily retract. I figured this was a result of either gummed up internals or air in the caliper itself, allowing pressure to be built up and retained.

The brake handle also felt rather squishy, and you could hear what was very clearly air bubbles in the master cylinder and brake line.

Using the brake handle to slowly push the caliper assembly apart, I was able to remove the brake pad and piston.

Brake caliper showing cylinder, gasket groove, and pad recess.

The internals didn't look too bad. I wiped out as much of the gunk that I could and pulled the old rubber gasket, then dipped the caliper and piston in Gunk carb dip for about 30 minutes.

Outer end of piston.

I then went back over the inside surfaces with a Dremel and steal wire brush to get the loose rust and surface pitting knocked down. After that, sanding with 600 grit wet/dry sandpaper and some WD-40 made the cylinder and piston surfaces nice and smooth. I also went over the inner pad walls to hopefully prevent the brake pad from hanging up.

Inside piston surface.

A quick test fit showed that the piston moved freely inside the caliper, and that the pad had plenty of clearance. Reassembling, I used some WD-40 to lubricate, and installed a brand new gasket. I compressed the entire assembly before reinstalling on the caliper swing arm to minimize the amount of air that would need to be bled from the system.

Back side of the brake pad showing nylon spacer.

I took a hint from various forums online and picked up a Speed Bleeder. They're about $7 and well worth the money. The old bleeder was getting rather nasty, so I wanted to replace this part anyway. For the record, the correct side for a 1977 Honda CB550K is 7.0x1.0mm, or part number SB7100.

Speed Bleeder. 

The Speed Bleeder is really a simple concept, but makes bleeding brakes a hundred times faster and more effective. It just has a spring loaded check valve internally that automatically closes the valve after you're done pumping the brakes. Attach a clear hose to the end so you can tell when the air bubbles have gone away and you're set. Bleeding the brakes on this bike took less than a minute, and I'm confident that I got 99% of the air out of the system. This combined with the stainless steel lines, rebuilt master cylinder, and rebuilt caliper resulted in very hard and sensitive brakes with no detectable "squish."

Fully assembled brake caliper.

Mobile APRS rig

What I have here is my mobile APRS rig. I originally put this together sometime around October 2011, but didn't fully refine it until late December 2011.

For those unfamiliar, APRS, or Automatic Position Reporting System, typically combines a GPS receiver and an amateur radio of some kind, with either a standalone tracker, computer, or other device in between the two which takes telemetry data from the GPS and transmits it over the radio using the typical AX.25 packet radio signalling, but in a more or less unidirectional mode. Each packet will usually contain a callsign and optional ssid, a short text message, and your position (or weather telemetry, but I won't go into that here).

Receiving stations can pick up these packets and display the position of every station that has been heard on a map, and also track stations that are moving by interpolating their path over multiple position reports. At the same time, receiving stations called I-Gates can "gate" your packets to the internet, or APRS-IS, enabling your position to be tracked over the internet. Other receiving stations called digipeaters can repeat your packets according to certain algorithms involving hop counts and station type, enabling your position to escape otherwise dead zones over long distances or high mountains before finally reaching an I-Gate, making the system more reliable than cellular signals in some respects.

An APRS station that only transmits is called a tracker, and is most often used in personal or mobile configurations. What I have in my mobile tracker is an old RadioShack HTX-202, a Byonics TT-3+, and an old DeLorme Tripmate serial GPS receiver (not shown).

The package is housed in a watertight storage box with feed through connectors for Anderson PowerPole +12VDC input, BNC for 2M RF, and DB-9 for serial and power out to the GPS.

I've also included a low-pass filter to deal with alternator noise that I was having issues with, which consists of about 20-30 turns of wire wound on a closed stainless steal quick link and a sizeable electrolytic capacitor.

Internal view showing low-pass filter and feed through connectors

The TT-3+ is configured using a null-modem serial cable and the included software, and is configured to pass through +12V to the GPS. The GPS itself has been modified internally with a simple LM7805 regulator and some caps to take the +12V from the tracker unit and regulate it down to +5VDC in order to replace the stock battery pack. The receiver was then spray painted flat black (originally they're bright yellow), and fitted with a hard drive magnet so it'll stick to the car roof.

BNC bulkhead connector and DB-9 male

This rig is for 2M, transmitting on 144.390 MHz, the standard APRS operating frequency. For antenna I'm using an MFJ-1721 1/4 wave mag mount, which is about as inconspicuous as you can get on 2M.

Anderson PowerPole panel mount adapter plates.

Power is supplied through Anderson PowerPoles and a standard cigarette lighter outlet (for now). At this point I'm rather undecided regarding PowerPoles as a legitimate power connector. They're rather pricey, can be difficult and expensive to crimp and assemble right, feel cheap, and can sometimes fail if the contacts are bent even the slightest. I'm very much considering switching over/back to the venerable "T" connector. <rant>Just look at the prices of some of the "Rig Runner" distribution blocks for the PowerPole. What a load of overpriced junk! That's not to say that the larger size powerpoles as used in large DC power systems like fork lifts and UPSes, but the low current sizes are really only good on paper.</rant>

I highly recommend Byonic's products, particularly in kit form. The instructions for their kits are reminiscent of the old Heathkit or Ramsey Electronics kits, and are rather pleasant to follow for even a seasoned electronics enthusiast like myself.

I'm now gathering components to make a self contained personal tracker based around an Icom micro-2AT. More on that when I start the build.

Anyway, you can track me via aprs.fi/KB3EWY-12 or any of the other online APRS systems using that callsign and ssid.

CB550K update

Today I had a chance to roll the bike outside for a quick photoshoot. This marks the first time the machine has seen daylight since I picked it up in early January of this year, and only the second time that it's been outside at all since the early 80's.

 More pictures here: 1977 Honda CB550 Four K

Last night I managed to get the rear brakes adjusted properly, wire-tied the cables along the frame and handle bars (note to self: handle bar bolts need to be torqued to spec), and got the front brake lines tightened and bled.

I have a feeling I'm going to have to pull the brake caliper off again and use the now-working master cylinder to push the pad and piston out of the caliper for cleaning. The piston doesn't seem to want to retract after you squeeze the brake handle, so I suspect it's gummed up or has air. The brake handle also feels rather squishy.

I'm also not sure that I got the clutch cover / clutch push rod assembled correctly. I have the adjuster screw backed out all the way, and the lever adjustment notches still don't quite line up. It also doesn't quite want to disengage, or is sticking in some way. Fixing all of this involves draining the oil and pulling the clutch cover again, at a minimum.

After those issues are worked out, I only have to apply the POR-15 tank repair kit after I get the tank back from the paint shop (which will happen within days of me receiving the new decal set in the mail), then install the tank, sync and adjust the carbs, get the bike re-registered and inspected, and get my class M permit. Not necessarily in that order.