Topic: Need help from those who completed dual disc upgrade.

[hevykevy420]

I'm having some trouble with the dual disc upgrade on a k8.  I've modified the speedo plate by cutting the edges off and hammering flat.  I'm still having to squeeze the wheel inbetween the forks, and the axle is not screwing into the receiver piece as much as it looks like it should, and the wheel does not look centered between the forks.

I think some people have foregone the chrome trim ring over the speedo plate, but it seems this will cause a pinching effect, and the whole assembly will be screwed up.  What am  I doing wrong here?  I have all the write ups/FAQ's on the upgrade and I've searched the forums but I can't answer my own question here.

Also, do you guys use new brake pads for the 2nd "new" caliper?  the reason i ask it it looks like mine is angled where it contacts the rotor, (the pads are used, they came with the ebay caliper.)  I know you have to fit the caliper carrier properly by shimming/filling, but I don't want to file for an already angled and used brake pad if the 2nd caliper will not work with new brake pads when the time comes for a replacement.

[RSV12K]

I have a 77 and have taken a look at what it would take to set up dual disks. My test fit went smoothly--wheel centered, no squeezing etc.

I've always assumed the speedo plate was the same for the 77 and 78... The base of my plate flat and has "ears" on two sides. To make that plate fit flush requires milling the back of the rotor. Maybe that's what you need to do? Seems like your set up is too wide, and the only thing I can think of is that plate not fitting fully into the rotor.

If you have the other speedo plate (I assumed it's pre-77 but it would be easy to be wrong) and you cut those tabs off, how is it going to work with the speedo drive? There's nothing there to engage the inside of the speedo, I guess.

You have to jettison the chrome ring.

Carpenter at CB750cafe.com (not sure of the URL) had some instructions he set me, which involved milling the back. I couldn't fit them on his site and I can't find them on my PC either. You might want to check with him.

Sorry, not much info, but it does seem that the problem is with the plate, no matter which one you have.

If you need a picture of the set up I'll be using, send me an email mjalex007 at yahoo.com

[mcpuffett]

Hevykevy, here are some pictures of the modifications you have to do to the speedo drive & hub on the 750, also Ben Hiles did a very good piece on the dual disc set up have a look in the searches,

cheers mick.

[MRieck]

I did away with the straight through bolts by putting helicoils in the hub. I used metric flat head allen screws on the speedo side to eliminate clearance issues. That required making 42 degree cuts in the bolt holes. The right side uses bolts

[KB02]

And yet another question to throw into the fire:
My bike is a 76 750F. I have my 78K Parts/Project bike that I can take a disk off for my second disk. I have everything else I need for the conversion except a caliper. Will the disk from the K8 fit? They are both spoke rims.

[mcpuffett]

As far as i can remember yes they should fit, cheers mick.

[RSV12K]

I don't know about the F models, but the diameter of the disks on the  pre-77 CB750s are larger.  I tried to install a pair n my 77 othat I sourced from a pre-77 and they wouldn't fit with the 77-78 caliper bracket installed. the rotor hit the underside of the caliper--between the pads, in other words. My explanation is not that clear, I know. Suffice to say, compare the size of both rotors before you find out the hard way what works or doesn't work.