Topic: CB750 dual front brake conversion question

[hatchb4ck]

I've gathered up most of the parts for my dual front disk brake conversion on my 75 CB750 SS project, but when I tried to fit the CB550 speedo drive through the disk, it didn't fit.  I'm doing a bit more inspection on the existing speedometer drive to compare, but I thought that I'd check if anyone has any info on the variance in size between the drive on the cb750 verses the one from the cb750.  I guess the other question would be, what is the diameter of the center hole on the cb750 disk?

I was there when the drive unit was pulled off the cb550 wheel.

Once I get a bit farther into mocking up the project, I'll start a thread and post some pics.

Thanks in advance!

Joe

[gerhed]

I did a dual setup on my'75 F, but used stock F cable--fit fine.
Cable drive on the axle had to be pared down about a quarter inch.

[hatchb4ck]

You wouldn't happen to have a picture of what the drive looked like after it was pared down?

[MCRider]

There are a ton of threads on this subject, with pictures. There was even a member who had machined several of the speedo drive plates.  Thre was a FAQ here that was a step by step for the conversion, and included a reference to a CB550 speedo drive plate. It has been determined this is an error. I don't know why we've nver been able to get that article updated.

I had one made for my project. I also ground down a stocker with a bench grinder and vice grips. 

But the CB550 one will never work. I'll try to find my pictures or a thread.

[MCRider]

here's a good thread. Good pic in reply 3. Mine is reply #11.

http://forums.sohc4.net/index.php?topic=53532.0

I searched on "speedo drive plate".

[scottly]

I guess the other question would be, what is the diameter of the center hole on the cb750 disk?

Joe

The center hole in a CB750 disc is 60 mm. (actually measures 60.2 mm, or 2.370")
If you do a search for dual discs, you may find Rookster's solution to the speedo drive plate situation, which is the most elegant I've seen: it involves machining recesses into the back of the disc to accept the flanges on the drive plate. 

[Rookster]

Thanks Scottly. 

Here is the link to the write-up I did on dual disks: http://forums.sohc4.net/index.php?topic=91781.msg1025007#msg1025007

Here is the pics that you may find interesting.  The rest of the write-up deals with K1 forks (C type caliper clamp) and a Lester front wheel.











Scott

[HondaMan]

Thanks Scottly. 

Here is the link to the write-up I did on dual disks: http://forums.sohc4.net/index.php?topic=91781.msg1025007#msg1025007

Here is the pics that you may find interesting.  The rest of the write-up deals with K1 forks (C type caliper clamp) and a Lester front wheel.











Scott

Nice setup, Rookster!
If the "swing weight" feels excessive on the dual-heavy disk setup, you can also swap the forks around and put the calipers to the back. Although this lets a little more water get in the pads during rainy rides and requires about 2 disc turns to dry out when grabbed, it was a help on track bikes by lightening the handlebar forces into and out of turns at speed.

[MCRider]

"you can also swap the forks around and put the calipers to the back. "

Like this:

[bollingball]

"you can also swap the forks around and put the calipers to the back. "

Like this:

MC Is that a stock headlight? For some reason it looks larger and not as deep maybe just tha camera angle.
Ken

[MCRider]

Ken: the beam unit (which is a Cibie) came from my original K2, a direct 7" replacement. The shell/ring combo came from CycleRecycle Part II, though I'm sure many others have it. It is marketed as a CB750 replacement item. But in fact i think it is a Kawasaki OEM/look alike unit. The Honda OEM, besides not being chrome, is more fully rounded. The Kawasaki is radially concave, as this one is. I was afraid it wouldn't hold the ratsnest of wire, but it does easily along with a HondaMans dual relay setup.

I think the Headlight ears push it slightly forward, making it look different.

[Elan]

another option is the speedhut gps speedometer. its still got a needle  and looks fitting on our bikes. And someone on here fitted it right into the stock speedo housing with no modifying.

You can even customise the gauge on their site- logos fonts etc.

http://www.speedhut.com/gauge/GR338-GPS-01/1/GPS-Speedometer-Gauge-120mph

I cant remember if its the 3 3/8 or 4" one that fits though.

[MCRider]

Cool! But it tops at 120?   

[Elan]

Cool! But it tops at 120?   

they have a 200 one

They also have one with a built in tach too, drool.

[MCRider]

Cool! But it tops at 120?   

they have a 200 one

They also have one with a built in tach too, drool.

Yeah, 200, that's more like it.   

[hatchb4ck]

Wow, thanks for all the great responses and pictures.  I do apologize for the redundant question.  I finally got the search results to show me those images.  I really like the idea of the machined slots in the back of the rotor.  Sometimes I wish I had a hobby size mill for small things like this.  I can think of hundreds more projects that I could come up with if I could do my own machining.

Once I get my CB 350 engine build completed, I've got an 74 xr 75 that needs to have a seal replaced and the forks rebuilt, then it's on to the two CB750 projects laid out in the basement.  One is a 75 Super Sport (unfortunately the PO cut off the left side passenger peg mounts already or I'd leave it stock) that I plan on making into a half faired cafe racer (dual disks on this one) and a 76 K series that will be a bobber.

I plan on getting the Hondaman book between now and when I start on these.  I look forward to sharing the projects with the forums for input and knowledge sharing.

Thanks again for the great information.

Joe