Topic: Rear disc conversion...what is there to know

[babyfood1217]

howdy all, as I sit here trying to find the best way to cover my seat and figure out a way to mount it to the bike, I'm been turning my thoughts to other project ideas.  The first is converting to a dual disc-setup up front, but so far I haven't been able to find all the parts necessary to do so, so that can wait.  Next is converting to a disc setup for the rear wheel.  I'm running a 1976 cb750k, so right now it has a drum brake, and I guess I am wondering what would be the easiest way to go about getting a rear disc?  Should I...

-Swap out rear swingarm and wheel entirely? (I want to retain spokes and wheel size)

     or

-Is it possible to retrofit a caliper to swingarms like mine (non-disc setup arms that is), ie: is there simply a bolt on method?  Then I guess I would need a new wheel regardless

I guess I'm not sure which bikes would be the easiest to do the swap with, so if anyone knows, please share the wealth.

Thanks-  Chris Gerber

[jotor]

howdy all, as I sit here trying to find the best way to cover my seat and figure out a way to mount it to the bike,

Put on a pair of pants, throw one leg over the bike and set down.

He, he, he.

[Egil]

Back in the 1976 the  CB750F1 super Sport  had spoked wheels whit singel disc at rear end 

Hope it`s help on the way!

Egil

[Geeto67]

I am wondering what would be the easiest way to go about getting a rear disc?

The easiest way would be to get a 1975/76 cb750F swingarm and rear wheel. Then all you would need to do is weld on the mounts for the mastercylinder and use a cb750f rear brake pedal. Keep in mind these are 70's brakes which means they are only marginally lighter and have marginally better stopping power. Everything is a bolt on except the master cylinder mount and works with the bike from the start so at least you can trust everything to fit.

Really is there anything wrong with the drum that you want to get rid of it? The drum on my 75 is by far one of the best drum brakes I have ever used and outstops many disc brake setups of the same or slightly newer vintage. As long as you maintain it it will serve you well.

If you really don't mind spending buckets of cash, the easiest way to get a modern bike rear disc on the back of the bike is to find a wheel similar in dimension to your stock cb750 wheel (like a sportster rear wheel or a fzr400 rear wheel) and have jmc make a swingarm for it (www.swingarm.com). R6 and triumph t595 rearsets have the mastercylinder mounts attached and only require to bolts per rearset to mount so you could probably adapt them to work on your frame (weld to lugs and bolt that sucker on).

Since cb750 front brakes suck it might do you some good to just upgrade the calipers or find a different front end. If you are trying to do the disc conversion spelled out on this site you will have a hard time finding the speedo drive ring you need and will probably overpay for it if you find it at all. A better way to go would be just to adapt a 75-77 goldwing front end (which is a bolt on conversion). A lot of kawasaki triple guys have had success with mounting ex500 and zx6 calipers to their preexisting setups using an adapter plate that bolts to the fork. Most have found this caliper to be so effective that you only need one to outbrake the 70's dual brake setup. I think this caliper may work on a cb750 disc brake rotor also so you may want to investigate that option.

[SkullCrusher]

Glad I saw this. Was going to do the dual disc conversion but may be easier to find the gold wing front end.

[Killer Canary]

How did the underseat exhaust turn out, Gerber?

[750K]

CycleX makes a bolt on rear disc set up, it's not cheap but it looks like it'll do the trick and keep the rear spoked wheel.

[Don R]

 I have a 76 super sport with dual stock front discs and a stock rear disc. I'm betting it stops as good as any sohc 750 around. You can modify your speedo drive. I did mine with a few hand tools and files.
 Custom swing arm sounds expensive, find an F model,  the 75 and 76 have spoked wheels and rear discs. I have a wrecked one in the shop waiting for a project that needs it.

 I do practice stopping, as it can save your life and totally support any effort to improve braking. I can make the tires beg for mercy while stopping, not sure how it would stop quicker. Better tires maybe?

[scottly]

Zombie thread??!!

[Don R]

The dual front brake add is relatively easy, it uses stock parts, just flipped over. I've been lucky enough to have a parts bike or two. Maybe that makes it seem easier.

[flybox1]

The dual front brake add is relatively easy, it uses stock parts, just flipped over. I've been lucky enough to have a parts bike or two. Maybe that makes it seem easier.

+1
once the parts are on hand, a dual front disc conversion can be done in a day.

[Geeto67]

The dual front brake add is relatively easy, it uses stock parts, just flipped over. I've been lucky enough to have a parts bike or two. Maybe that makes it seem easier.

Stock parts flipped over, one lug trimmed and a spacer made. It isn't just flip it over and bolt it on, otherwise the swing bracket is going to be cockeyed. Still you are right it can be done in a day. easily.

the advantage of the GL1000 front end isn't just the dual discs and being a pure bolt on, it is also 37mm forks and a slightly wider fork spacing. 35mm forks really aren't all that great for a 500 lb motorcycle.