Long time no update...  So one of the few complaints about Honda's CB is braking performance. I had noticed that the front end appears to lend itself to dual discs with a few minor modifications. Further investigation on google indeed proves it can be done, so prior to buttoning up the front wheel and balancing it, I set off to convert to dual discs.

Obviously the first step was to get another brake rotor, caliper, and caliper bracket which is easily accomplished thanks to eBay. I studied others attempts at performing the conversion. Although many appeared successful, they were fairly crude. I was determined to find a better way. After taking a few measurements, it was obvious that the trim ring (AKA gear box retainer cover) would get tossed, and the speedometer drive would need modification to "slim" down the overall thickness, to allow the brake rotor on the speedometer gearbox side to fit. It is normally the trim ring that captivates the "ears" on the speedometer drive. The speedometer drive then engages the gear in the speedometer gearbox, which in turn drives the cable attached to the speedometer. Simple enough. This all assumes you want to keep the mechanical speedometer - I did. Although I realize that my speedometer will not be "correct" as I will have a larger than stock front tire... But I digress.

Without the trim ring to captivate the speedo drive, I needed something new. I realized that if you place the "new" brake rotor on the front wheel (speedo gearbox side), it creates a pocket nearly equal in depth to the thickness of the flange of the speedo drive. So my solution was to have a buddy of mine (thanks Kenny!) chuck the speedo drive in a lathe and turn the OD down such that it fits within the bore of the brake rotor, and then simply install a couple small #4 flat head cap screws to attach it to the front hub. This requires drilling and tapping the front hub, but its really not a big deal. The slip fit between the OD of the speedo drive and the ID of the brake rotor centers the speedo drive, and the 2X FHCS fixes it in place, allowing it to drive the speedo gearbox. We there? Hello? If you arent following what I'm saying, the pics below may make more sense. Note that if you wish to replace the oil seals in the speedo gearbox, the smaller one is a 4.8X15X4 (search for Honda #91256-240-003), and the larger one is a 34X48X7. For the time being, I'm using the old oil seals as I plan to eventually have the speedo drive gearbox housing powder coated.

Next I performed an optional step: Drilling the brake rotors. Back in the day, drilling brake rotors was done for good reason. I'll spare you the details, you can google it. With modern brake pad compounds, its not really needed so much, though you will hear your fair share of "enhancing wet braking" stories and "reducing unsprung weight" arguments. Some have merit. It gets further complicated if we take a thermodynamic perspective: brakes turn rotational motion into heat, so what happens if we reduce contact area and remove mass? Bueller? Long story short, there are many arguments for and against drilling rotors. I did it mostly because I felt like it. And if you are curious, my drill pattern reduced the weight of each rotor by ~0.19 lbs.

Drilling rotors is not rocket science. I started by creating a template with a pattern I liked. For those interested in my template, click here for the 8.5X11 version, or click here for the 11X17 version. Note that the 8.5X11 version will need to be joined together to create 1 complete template. Also be sure to print the templates actual size with no scaling. I opted for 0.25" dia. holes spaced such that I get maximum hole-to-hole wall thickness to prevent cracking. I taped the patterns on the rotors, and center punched them. I then setup my el-cheapo bench top drill press (in the living room!) in a box to collect all the chips. I used a couple quick clamps to hold the rotor in place. The secret to this job is to use a cobalt drill bit, with cutting fluid, at around 600-700 RPM. I used a Bosch bit, with tap magic as cutting fluid. Once done, I used a countersink bit to deburr and countersink the holes.

With that all accomplished, I was able to assemble the front wheel far enough to balance it. I used the same process prescribed in my previous blog post. The front wheel took a bit more weight than I hoped (60g) - its not the end of the world, but I may go back and break the bead loose and move the tire around on the rim to try and make it better. Also note that in order to torque the front axle correctly, you will need a 23mm deep socket that has at least a 1.5" deep engagement. I found that my impact socket was not cut deep enough, and had to purchase another (Lowes had one that worked). Make sure to put a bit of anti-seize on the axle threads to prevent the aluminum axle nut from welding itself to the axle.

You will notice that only the hubs have been powder coated, and most of the other components (brakes, calipers, brackets, etc.) were left alone and are fugly. My intent is to build the bike first, and then it will be torn down, probably more than once, for paint/coatings. I jumped ahead on the wheels, as I do not wish to re-lace, re-true, and re-balance all over again.

It was finally time to fit the completed front wheel assembly to the bike. And it almost fit! Turns out the fork braces built into the front fender interfered with the tire. The solution was easy, I carefully "flared" them around an old piece of exhaust tubing (~3" OD), which provided me with enough clearance for the tire. While I was there, I also opted to shorten the fender. I like the "classic" look of the fender struts, so I opted to shorten the forward side of the fender and eliminate that strut, but keep the aft portion of the fender the original length with the strut. Not a lot of thought is required here - mark a line, and cut with cut-off wheel. Keep cutting until it looks good. 

A larger master cylinder should be used to drive the dual discs. There are many options. I am using one from a mid-70's GL1000 Goldwing. It has similar "styling" to the OEM master cylinder to retain the classic look, but uses an 11/16" piston for driving dual calipers. I found mine on eBay - it was beat up and worn out, so I got it for cheap and rebuilt it. K&L makes a rebuild kit, and new reservoirs can be found (I got both on eBay). The master cylinder required significant cleaning, and it was a bear to remove the retaining ring, even with the appropriate tool. I lightly honed the bore, and verified it was within spec with my mic. I opted to use my aluminum OEM reservoir cap rather than the new plastic version.

One important final step is to shim the caliper brackets as required to ensure than they are square to the rotors. I simply used washers and found that the original caliper bracket was fairly square, but the new one needed adjustment. I also found that I had to use a button head cap screw on the upper-most caliper bracket attachment for access reasons.

The existing caliper adjustment bolt/spring can be used with the new brake caliper bracket, you just need to place the jam nut on the inside of the flange, rather than the outside. I, again, opted to take a different route: I had my buddy Kenny turn a blank on his lathe that is longer than the OEM bolt (thanks again Kenny!). I was able to cut the threads with a die, and the slots with my dremel. I then found a slightly longer spring at the hardware store. What can I say, I'm a sucker for symmetry.

Finally it was time to button it all up. I used a ton of new parts (listed below). In regards to the lines and such, I opted to go with a modular banjo style setup, making it easy to customize. I got rid of the factory caliper hard-line in addition to the 3-way brake joint where the OEM brake light switch attaches. I also opted not to use the rotor dust covers. You will notice I clearanced the speedo/tach bracket so that there would be plenty of room around the new brake lines/fittings. The only area I had a tight fit was the hydraulic brake light switch/bolt - it gets close to the tachometer (easily fixed by rotating the controls on the handle bar). Below are the new parts I used, inclusive of the rear brakes:

- Goodridge speed bleeders, 7mm X 1.0 pitch, and new caps
- Goodridge crush washers: Use at banjo interfaces
- 4X Goodridge 3/8-10 35 deg. banjo fittings: One for each line at the master cylinder, and one for each caliper
- 2X Goodridge banjo bolts, 10mm X 1.25 pitch: Use at calipers
- 26" Goodridge brake line: Rider right
- 30" Goodridge brake line: Rider left
- K&S hydraulic brake light switch, double bleed, 10mm X 1.25 pitch: Use at master cylinder
- K&S rear brake light switch, mechanical, universal
- 2X EBC FA13 Brake Pad Sets, Kevlar: Front
- EBC 316 Brake Shoes, Kevlar: Rear

From here I bled the system, and everythign seems to be working fine. Needs a road test to be sure. The only thing left is to figure out some brake line clamps - I'm thinking P-clips or similar. For now I simply have the lines zip-tied in place. Also note I am using, and recommend, ATE brake fluid. Some prefer "super blue," however it has a tendency to stain reservoirs (but makes it easier to determine if you have flushed the system). I prefer the standard ATE type 200 DOT4, which is the same as super blue, only without the blue dye.

10/18/2013 03:23:29 pm

good post

4/4/2014 11:47:25 pm

Hi there

Great guide! I really enjoyed reading this. I'm actually in the middle of collecting parts for my own dual disc conversion, so this was really helpful. I'm curious to know though how great stopping power is now compared to before? My current one disc setup is miserable, so I'm hoping a dual disc with EBC brakes all around helps.


Soeren, Denmark

4/5/2014 12:58:06 pm

Thanks Soeren! Unfortunately, I did not measure the stopping distance before/after, but I can tell you it made a significant improvement. I think it is well worth it!

4/6/2014 05:41:43 pm

Thanks, that was what I was hoping for :-)

Did you sand/grind your discs afterwards and if so, what did you do and how?

4/7/2014 01:30:18 pm

Hi Soeren,
I deglazed the rotors with fine grit sandpaper. Mine weren't quite bad enough to need grinding yet.

4/27/2015 11:05:48 pm

Looks great! Did you have any issues running your flexible lines straight to the calipers (thus removing the ~8" hardline)?

4/28/2015 01:00:09 pm

Hi Nick,
Nope - it wasn't a problem, though some sort of attachment bracket (or insulated "P clamp") might be nice somewhere on the forks.


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