Topic: Rear 750F disc brakes on a 750K frame?

[JBCB500]

Is this a straight fit or are modifications required?

I have a dual disk front end that I plan to fit on a comstar wheel and I would like to fit a disc to the rear as well.

If not, is it straightforward enough to put dual discs on a factory wire wheel?

[flybox1]

Front isnt too much work...
http://forums.sohc4.net/index.php?topic=53532.0

[JBCB500]

Thanks Flybox.  I assume my front will be even easier still as I have a dual disk setup straight from an F.  I assume it'll slide right in to the trees and I'll just need to use an F master cylinder and lines??

What I'm more curious about is whether the rear setup from an F will go straight onto a K?

[flybox1]

Thanks Flybox.  I assume my front will be even easier still as I have a dual disk setup straight from an F.  I assume it'll slide right in to the trees and I'll just need to use an F master cylinder and lines??

What I'm more curious about is whether the rear setup from an F will go straight onto a K?

I dont know for sure.  Someone will chime in soon...

[TheArchitect]

I picked up a 75' 750 in which the previous owner did this conversion. The front was straight forward as suggested. In the rear, the P/O  used the aluminum foot peg/rear master cylinder aluminum brackets that came on the 750F. This mounts the master cylinder and pegs, the reservoir to the master cylinder attached to  a tab to the frame above.

It required modifying the frame to get the aluminum supports to fit properly, there are some bits on the frame that protruded too far. The rear triangles were cut off as well, I think this might have been neede for clearance for the F brake arm that is on the swing arm. Maybe, not sure.

He also used the F swing arm.

If you were closer, at some point I was going to sell the modified frame with all the F stuff because I am making it back to stock.

I can send photos via email, photo bucket crashes my computer! 

[JBCB500]

thanks TheArchitect!  I've sent you a PM as I'd love to see those pics!

I also have a couple of F frames available but they'll be more difficult and costly to title.  I hope this isn't a back-asswards way of doing things!

If it looks like too much trouble I guess I can live with the factory setup for K brakes.

[JBCB500]

By the way I do have a complete F swing arm with comstar and disc brake.  It sounds like the setup you are describing is exactly what I'm looking to do. 

Anyone else got a how-to?

[754]

If the K frame is 76 or earlier your shocks will angle out.

[JBCB500]

If the K frame is 76 or earlier your shocks will angle out.

How do you mean?  Like they will angle outwards and down because the F arm is wider where they mount?

[754]

Yes , and the F arm is longer as is the frame, so your bike may lower slightly.
 It can all work, just know this ahead of time. The F had the aluminum peg mounts on the side, to use them you will need the longer swingarm pivot.

[CB_Jeff]

It has been done, check out Prokop's The Red build:
[url]http://forums.sohc4.net/index.php/topic,115305.0/url]

[JBCB500]

It has been done, check out Prokop's The Red build:
[url]http://forums.sohc4.net/index.php/topic,115305.0/url]

Thanks Jeff - that build looks a lot like the one I'm embarking on!

[Don R]

 It can be done but is not a bolt on deal. Fabrication required.

[Rookster]

It can also be done using the stock K swingarm and wheel.  The caliper is a Hurst Airheart.  The Master cylinder is made by MCP and uses the stock rear brake pivot with a custom rod to activate the pull master cylinder.  The swingarm is a Dresda replica but the width is the same as the stock K swingarm.  You can see the brake stay is the stock drum item.  The rear wheel has the drum setup from the K bike with a custom made disk carrier that bolts in place of the drum plate.  The disk is a cast iron AP Lockheed item that was used on some Triumphs, Nortons, and Ducatis.  There are many different options for a rear disk setup on the K bikes.



Scott

[JBCB500]

If the K frame is 76 or earlier your shocks will angle out.

I note that Prokop moved his shock mounts, so I'll ask him the same question.  I've attached a couple of pics of my F2 arm mocked up on a K6 frame, and I don't see where this clash will occur?

[CB_Jeff]

That does appear to line up well.  You will need to fab up a bracket for the rear MC to get the rear brake pedal to work.  I recall that being a tricky part of the Red's build.

[754]

You can see chain side shock angling out, you can run a spacer, inboard on the top mount.

[seanbarney41]

If you ride the bike with shocks that are not parallel, you will soon notice that the rear suspension jams, resulting in a hardtail Like ride and the shocks will start leaking soon thereafter