Topic: dual front discs Honda factory option?

[Hondawggie]

Back in the early years, 1969 through, say, 1975 -- was there an option to purchase from Honda a 2nd brake caliper and rotor for the right side of the cb750 fork?  I'm wondering if Honda would have made this available as an option.

Maybe as part of a racing kit for the 750?

[bryanj]

Yes, but it was dammed expensive as all the cast parts were magnesium alloy

[Hondawggie]

Yes, but it was dammed expensive as all the cast parts were magnesium alloy

Would the same cb750 master cylinder have been used, and maybe only a splitter and an extra brake hose added below the stock master cylinder?

[kmb69]

They also offered a CR (-970) master cylinder with a 5/8" piston. EXTREMELY hard to find. Have only seen 2 on eBay in the last several years and bid to low on both. You can use an early Goldwing master cylinder or most any of the single piston caliper dual disk master cylinders to get the proper hydraulic action. The stock master cylinder will feel kind of spongy but some guys claim to like it.

[mjstone]

I used a GL1000 master cylinder on my CB500 when I converted it to dual disk.  Works great!  Oh, get braided stainless steel brake lines too.

MJ

[jay_m]

what did you guys use for calipers when you did this?

[BobbyR]

The later F models had dual discs. I have a 78K and the fork leg has mounting holes. I bought the speedo, and splitter and a caliper arm on ebay. I am not sure if they used a different MC. I have not put it on the bike yet.

[jay_m]

yeah, my k6 has the extra mounting hole. just searching for a caliper and mounting hardware thatll fit.

[BobbyR]

You will find a lot of threads on doing it

[mjstone]

I used a complete caliper and mounting bracket for a 500/550.  On my CB500 it didn't have the mounting points on the right fork leg that is necessary for mounting the caliper arm so I needed the right lower fork from a 550 to do this.  I bought a complete set of forks and all the brake parts I needed from a forum member that had them ,from a '75 550, for sale here on the forum.  That gave me most of the parts I need to do the conversion.  Since I had both complete forks from the 550, I decided to use those on my 500 so I could upgrade to cartridge emulators in the future if I chose to.

If you are looking to do this to a 750 you will obviously need to use parts from an appropriate 750.  You should also look at getting a speedometer drive adapter from forum member rangelov.  You can find this in the parts for sale section.

MJ

[HondaMan]

Ah.
You guys haven't read my book. 

It's covered in the Brakes section, how to add a second disc to either the K0, K1 or K4 series bikes. 

[Hondawggie]

Before I posted I did a 'search' and found dual disc stuff but really I was curious whether Honda offered a kit and didn't find the answer in the archive, although to be fair after searching on different phrases and not finding it I gave up.

So here's the deal.  My  1970 K0 has mounting holes on the right fork leg (but no caliper).
My '72 k2 bike has similar mount holes on the right fork leg -- and they just happen to be occupied by the right side caliper and support arm.

Next, I compared my K0 caliper and mount arm with my '72 caliper and mount arm (left side) -- they look the same on my K0 and my K2.

And the right side parts on my K2, caliper and mount arm -- are *identical* to the left side of both the K0 and K2 in terms of shape, detail (ie. fins on the outside of the caliper, the position/angle of the bleed valve), style.

The right side front brake parts on my k2 are a mirror image of the left side on my K2, and the left side K2 looks like my K0 -- so I have no choice but to believe

- Honda made my right side front brake parts

- or some manufacturer copied the machining detail and casting style/details of the stock Honda left side brake bits to supply identical-looking right side front brake bits.

Man this is a lot of unsprung weight up in front there.  This is the first time I've ever seen a dual disc setup on a cb750.

I am considering putting the front duals over onto my '70 k0 and putting my '70 k0 single disc on the k2.

The calipers on my k0 and k2 look identical.   

[mjstone]

They should be identical parts, not any mirror image.  The caliper arm just swings around on the pin 180*.  The caliper itself just turn it around so the fixed pad is on the inside and the piston is on the outside.  The only difference might be with the hard line and the bleeder valve.  On my 500 they are side by side so nothing is different.  Some of the 750s have the line and the bleeder in-line front to back.  You may be able to swap the line and the bleeder around.  Somebody else will have to confirm this though since I don't have this style caliper.

MJ

[Hondawggie]

They should be identical parts, not any mirror image.  The caliper arm just swings around on the pin 180*.  The caliper itself just turn it around so the fixed pad is on the inside and the piston is on the outside.  The only difference might be with the hard line and the bleeder valve.  On my 500 they are side by side so nothing is different.  Some of the 750s have the line and the bleeder in-line front to back.  You may be able to swap the line and the bleeder around.  Somebody else will have to confirm this though since I don't have this style caliper.

MJ

Mirror image meaning the left and right look identical just flipped through 180 degrees, at least the right side caliper is a 'mirror image'.  For example, the left caliper's bleed nipple points to the front.   If you just took a left-side caliper and tried to install it on the right side fork leg, at a minimum it would not look like a mirror image (the bleed nipple would be facing backward........)  Having never tried to swap a left side 750 caliper over to the right fork leg, I can't say for certain you could even do it.

[MCRider]

They should be identical parts, not any mirror image.  The caliper arm just swings around on the pin 180*.  The caliper itself just turn it around so the fixed pad is on the inside and the piston is on the outside.  The only difference might be with the hard line and the bleeder valve.  On my 500 they are side by side so nothing is different.  Some of the 750s have the line and the bleeder in-line front to back.  You may be able to swap the line and the bleeder around.  Somebody else will have to confirm this though since I don't have this style caliper.

MJ

Mirror image meaning the left and right look identical just flipped through 180 degrees, at least the right side caliper is a 'mirror image'.  For example, the left caliper's bleed nipple points to the front.   If you just took a left-side caliper and tried to install it on the right side fork leg, at a minimum it would not look like a mirror image (the bleed nipple would be facing backward........)  Having never tried to swap a left side 750 caliper over to the right fork leg, I can't say for certain you could even do it.

Its been done tens of thousands of times. Don't try to reinvent anything. Read Hondaman's book. When I did mine there was no book. Its obvious the leg lugs are there. Just take a second caliper set up, swap it over, reroute the lines as necessary and go. The bike in my avatar is a K1, brakes done in 72.

There is no kit, none necessary. Plenty of guidance on doing doublesdiscs.

Biggest hangup is the speedo drive and a forum member is offering new ones from bilet in the classified for sale forum.

Oh yeah you'll need somelonger bolts for the discs. Piece of cake.

[rangelov]

Shameless plug.  But sometimes hand holding is necessary.

I can supply the speedometer driver.  There are other ways of doing it yourself.  It's your time to do the research and labor.  Or just buy it and don't worry about it.

FYI, you need 8 mm X 110 mm long X 1.25 mm thread pitch brake rotor mounting bolts.  I can also supply these longer disc mounting bolts.  I posted links to the supplier, but people think it would be easier for me to supply them as well.

Click on the link in my signature.

[MCRider]

It was rangelov's solutions to which I referred. Best remedy to date. Great service to the community.

[scottly]

With the early finned calipers, you swap the bleeder and line by pulling out the steel flare seat and putting it the old bleeder hole. Attached is a pic of a K7 seat; I believe the K1 is slightly different.
To use a left-side "C" mount on the right side, some material must be removed from the lower mounting boss, and spacers added to the two upper bosses. Also attached is a pic of a magnesium right side mount.
I am just finishing adding a right side caliper to a K7 fork with the "T" type mount, and the lower boss on the fork leg is longer than the left. I machined off the flat on one side of the pin to properly locate the caliper, rather than add spacers to the upper mounts. Beware if you do this! Turns out the pin is VERY hard, and I wasted a HSS end-mill; use a carbide end-mill.