Topic: Completed dual disk upgrade 1978 CB750K

[Dolomite]

After a few weeks of acquiring parts and trial and error I completed my dual disks for my 78 750k. I was lucky enough to snag a full brake setup with mount off internet bidding for ~$60. I shaved maybe 1/16" off the bottom bolt mount for the caliper and a set of standard washers up top and it was nice and parallel. This may have just been a stroke of luck on my part. I removed the fender from the front brace and reused the brace. Also instead of doing custom lines which was going to be quite pricey I opted for a premade route. I used 12" 45* m10 banjo lines with an3 females for the calipers going to a an3 tee mounted to the brace, then a 24" 45* m10 banjo with an3 female from the MC to the tee.

[beemerbum]

Nice work!

[Don R]

 I did one with the same brakes. It was awesome. I had so much fun practicing panic stops I scalloped the tire.

[ladyrocket]

I just got my dual disc setup done about a week ago.  76F bike w/ a spare K8 caliper, arm, and disc.  I kept my fender on.  I didn't shave any off the right fork leg, so I had 0 washers on the bottom bolt, and 2 washers + 1 locking washer on the top bolts (the lock washer pressed into the fender hole w/ the rubber grommet removed - thanks Godffery!).

Don't have the bike running yet so I can't do any riding tests, but it seems fine just rolling and braking so far.  I've got braided lines and a 5/8" master from a sport bike.  Even with all of that the braking feel isn't as firm as I'd hoped.  My rear caliper braking feels rock solid after a bleed, but on the front I can tell it's grabbing hard midway, but I can just keep pulling the lever to the bar with more strength.  I've also noticed my caliper arms flex somewhat when the brakes are fully applied.  Is flexing of the arms normal?

[Dolomite]

I believe the mounts are supposed to flex (side to side) some along the pivotas they grab the disk, making it a semi fixed caliper setup? If someone can chime in and shed some more light on that.

I have a drum rear and with the 836cc kit and cx1 cam any increase in braking is a plus for me 

[Rookster]

Something has to float for a disk brake system to work.  Either both pads can float or if one of the pads is stationary then the caliper has to float.  Honda went the cheap route and used a single piston caliper which required a floating caliper.  This is achieved by the pivoting caliper arm.  Calipers moving is a good sign that the pivots aren't seized.

Scott

[Dolomite]

Is it considered a true floating caliper in it's design though or is it more of a hybrid? I thought true floating calipers, like the DOHC bikes, moved while the bracket was stationary.

[Don R]

 Rubber bands on the brake lever overnight can work wonders. "experts" say it won't help but I saw a photo of the Yoshimura shop and they were doing it, good enough for me. It compresses the air making it lose it's grip on the inside of the lines, the air floats to the top and the next time you cycle the lever it burps out.

[Dolomite]

I just used a set of speed bleeders when I rebuilt them so I don't have to grow a 3rd arm 

[Don R]

 I did those also. nice.

[754]

The pivot allows the caliper to swing in an arc for centering.
 The pads also have either a spherical  bump , or a spherical slug in the end of the piston, this allows the pads to always be parallel to rotor surface. Even if the swing bracket us at an angle to the rotor.  So remember there should be a bit of clearance between pad and where it sits in the caliper.

[70CB750]

Looking good.

[Erny]

This is on my todo list for the next winter break

[scottly]

I've also noticed my caliper arms flex somewhat when the brakes are fully applied.  Is flexing of the arms normal?

If the arms are actually flexing, vs swinging from side to side a tiny amount, you may have a caliper alignment problem. Try loosening the mounting bolts on the fork legs a far amount, then apply brake pressure; the caliper will try to align itself, +/- the range provided by the bump Frank mentioned.

[ladyrocket]

After a few weeks of acquiring parts and trial and error I completed my dual disks for my 78 750k. I was lucky enough to snag a full brake setup with mount off internet bidding for ~$60. I shaved maybe 1/16" off the bottom bolt mount for the caliper and a set of standard washers up top and it was nice and parallel. This may have just been a stroke of luck on my part. I removed the fender from the front brace and reused the brace. Also instead of doing custom lines which was going to be quite pricey I opted for a premade route. I used 12" 45* m10 banjo lines with an3 females for the calipers going to a an3 tee mounted to the brace, then a 24" 45* m10 banjo with an3 female from the MC to the tee.

Hey Dolomite, do you mind taking a look at your caliper shimming setup for me? Can you tell me exactly what you have bolted on from fork inward on each side and at each bolt? Ie the right side upper bolts: fork-brace-bolt and left side fork-brace-washer-washer-bolt. I want to double check my setup. I’ve been riding my bike and it hasn’t seized up on me, braking feels great while riding but when I lift my front end and spin the wheel it doesn’t really freewheel at all. Maybe spins 3/4 a turn before brake pad drag stops it.

[maxheadflow]

Does anyone reverse the forks and run the calipers behind the forks? Used to do that back in the olden days..