Topic: Fitting dual discs to a K2 question please

[Scott]

G’day, how’s it going

I have a CB750 1972 model and am looking at putting twin discs on it. I’ve had a mag wheel with twin disc sitting here for fairdinkum near 10 years and I might be ready to chuck it on.

I tried fitting it a couple of weeks ago when I had the front wheel off, but it appeared at a quick look that I had to pull the caliper to fit the mag and I stopped there.

So question is...... Any one got any tips or maybe know what master cylinder has worked well for them.

Thanks for your time and thoughts.

Scott

[bryanj]

When i did a 500 decades ago i used a gl1000 master with brakelight switch and removed the hydraulic brack switch to fit a banjo and bolt for the second caliper

[Doobie]

I put dual disks on a CB750 years ago. I don't recall the steps but everything I needed to know I found here using search. Dual-disk conversions must be one of the most discussed topics on this forum.... I used an MC from a Goldwing, which is what several people suggested.

[70CB750]

G’day, how’s it going

I have a CB750 1972 model and am looking at putting twin discs on it. I’ve had a mag wheel with twin disc sitting here for fairdinkum near 10 years and I might be ready to chuck it on.

I tried fitting it a couple of weeks ago when I had the front wheel off, but it appeared at a quick look that I had to pull the caliper to fit the mag and I stopped there.

So question is...... Any one got any tips or maybe know what master cylinder has worked well for them.

Thanks for your time and thoughts.

Scott

I done it on Dorothy, it was not hard.  And I used the original MC, thats all you need.  There is not that much fluid being moved.

[38rudge]

I too have done a twin disc conversion on my UK 1972 CB750K2 and have used the original master cylinder without any problems.

[MauiK3]

My original master works fine, good feel, does not bottom out. Have to bleed it all the way.
The big thing with the second caliper is to get the spacers right, I don't have measurements for mine but I can measure them if you need.

[scottly]

One more vote for using the stock 14mm master.
If your K2 is like the USA model, it uses a "C" shape caliper bracket to attach to the fork leg, while the later models use a "T" bracket; a left side "C" bracket needs to be modified to use on the right side, while the "T" bracket just needs spacers.
What type of mag wheel did you try to fit? If it was a Comstar, it won't work with the K calipers of either style bracket.
 

[Bankerdanny]

I fitted up a new, radial style master when I did the conversion on my F1. I opted for an F3 front end to make the conversion easier.

[PeWe]

My CB750 K6 got this mc
Work fine with dual brakes.
https://www.davidsilverspares.co.uk/CB750K2-FOUR-1972/part_123912/

My K2 has same mc with single brake.

Replaced the cheap looking cap.
https://www.davidsilverspares.co.uk/CB750K2-FOUR-1972/part_189665/

[Scott]

Thankyou for all the replys

I will try with my current master cylinder and I also have one of those ones from David Silver spares in my spare parts box.

I think what I will do now that I think about it a bit more is put another disc onto my wire wheel rather than fit the mag (Lester)

The caliper on the left side has the C type bracket same as USA K2 bikes, the only spare caliper that I can find in my spare parts has the T type bracket.  Do you think it's ok to use the T bracket on the right side while leaving the original C bracket set up for the left.

Thanks again
Scott

[Scott]

For the brake line I was thinking of getting a longer (double) banjo bolt and adding the second brake line to the same position on the brake splitter block as the existing brake line to caliper is fitted.

[scottly]

The caliper on the left side has the C type bracket same as USA K2 bikes, the only spare caliper that I can find in my spare parts has the T type bracket.  Do you think it's ok to use the T bracket on the right side while leaving the original C bracket set up for the left.

Thanks again
Scott

The T type bracket won't bolt onto the K2 fork lower; the mounting lugs are different.
Also, the Lester should be a direct replacement for the wire wheel, if it is meant to fit a 750.

[Scott]

Nice one mate, thanks for the info. I’ll try tracking down a C bracket.

I thought the Lester would go straight on, but then I would have wire rear wheel and mag front.

Now I put a bit more thought into it I could just add a disc to my wire wheel as the tire is new and the wheel is only 4 or 5 years old.

[Scott]

Any one with a C bracket for sale, I’m interested.

Any ideas where to search is highly appreciated.

I’m taking the bike to Tassy in February and thought it’s worth trying to get the second disc on if possible.

[38rudge]

You might find this link useful for the parts used and how I did mine during the conversion: http://www.sohc.co.uk/index.php/topic,21171.0.html

[Shtonecb500]

http://forums.sohc4.net/index.php/topic,190445.msg2215609.html#msg2215609

i had questions about my dual disc conversion for this type of bracket too. For my other 750 with dual disc and the later model  "T" caliper bracket, I remove the stock side bracket at the three mounting points, then drop my wheel out, then i can access/service the dual side caliper...installing goes dual side caliper, then the wheel, then the stock side caliper.

no clue if any of this info is helpful, take care.

[HondaMan]

My original master works fine, good feel, does not bottom out. Have to bleed it all the way.
The big thing with the second caliper is to get the spacers right, I don't have measurements for mine but I can measure them if you need.

I had duals on my K2, used "C" bracket with spacers under the right-side bracket), from 1972 until 1979. Used the standard master cylinder. The lever moved about 1/4" further than with 1 disc, but felt like 'power brakes' when grabbing! It could also make the front wheel lock easier if braking on sandy surfaces, tricky with heavy touring loads aboard.

[Scott]

Thank you very much for the reply's and info

I have half a thought that I bought a C bracket one time, but I can't find it so maybe not.

[HondaMan]

Thank you very much for the reply's and info

I have half a thought that I bought a C bracket one time, but I can't find it so maybe not.

You can use the 'T' bracket in place of it, if that's all you have.

[scottly]

Thank you very much for the reply's and info

I have half a thought that I bought a C bracket one time, but I can't find it so maybe not.

You can use the 'T' bracket in place of it, if that's all you have.

Sorry Mark, but the T bracket won't work in place of a C bracket. Believe me, I tried!

[HondaMan]

Thank you very much for the reply's and info

I have half a thought that I bought a C bracket one time, but I can't find it so maybe not.

You can use the 'T' bracket in place of it, if that's all you have.

Sorry Mark, but the T bracket won't work in place of a C bracket. Believe me, I tried!

I'm thinking of the 'T' bracket from a K3 bike: I used one to put duals on a K2 long ago (last year in my old bike shop, 1973 summertime). It's owner was jealous of mine. It had to be shimmed up much like the 'C' bracket, but it worked OK, came from a wrecked pair of K3 front forks (rear-ender accident).
I know the 'T' bracket changed on the K7, though.
What bike did your 'T' bracket come from?

Now I'll have to go back and sleuth through the Honda parts lists...?

------------------------------------------
Update: here's some research results from old parts manuals:
The K3 had a top clevis (Honda calls it the "Upper") that is #45104-317-700. This remained until the K6.
The front brake uses the same "Pin" from the K3 through the end of the 750K series (K8) that is #45116-367-690
The K7 used a new top clevis #45104-405-000. It probably has different hole-centers. It looks the same in their drawings, though(?).

Do you recall what didn't fit with the top bracket? Was it the hole spacing?

[scottly]

This pic shows a "C" bracket style fork lower, used from K0-K2 on the left, with the "T" style mount used on the K3-K8, plus the F0-F1 on the right. The F2-F3 are a completely different animal..

[scottly]

Now that I think about it, the arm the caliper bolts to are also not interchangeable between the two bracket styles, in other words you can't mount an early caliper arm to a T fork by merely substituting the C for a T. The positioning of the caliper over the rotor is different. Something to be aware of if the extra caliper doesn't line up, Scott. 

[bryanj]

The C bracket can be modified to fit the othe leg by removing part of one boss and spacers on two others

[Scott]

I’ve searched my parts stash and don’t have a C bracket and caliper set up.

I’ll keep my eyes open for one that is for sale, but haven’t found anything yet.