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Discussion Starter #1
Geeto, I know you're the 750SOHC guy, so I have a brake question for you:

I picked up a set of CB750F SS forks from Ebay (1978), and I was wondering just how different the brake calipers are between the various years - naturally none of the part numbers are the same - can later K/L model calipers fit? What about the discs?

Also, to anyone out there:

I'd like to upgrade my carbs from the CV Keihins to something a little newer - would any 32mm Mikuni work (properly jetted, of course)? I see some later-model (90's) sportbikes with Mikunis that have me thinking...

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1977-1978 F front brakes, forks, wheel, etc are the oddball of the cb750 clan (sharing only some parts with the SOHC cb750A). They are closer to the DOHC forks than any cb750 stuff previously. They will however slide into your trees, although the F trees were slightly different because of the F bikes having a slightly different rake.

The short answer is that the 69-76 brakes will not work on thos forks no way no how. Furthermore the earlier calipers will not work with the later disc because of spacing issues. If you are going to use the 78 F forks, you will need the calipers, rotors and wheels to go along with it. Furthermore you can't use the 78 rotors on an earlier wheel because even the bolt spacing is different.

There is one upside however, and that is that the DOHC 750Fs used almost the same setup in 79-80 and there is a way to adapt the 82 twin piston calipers (unarguibly the best cb750 caliper ever made) to the 78 front end and rotors. I think the DOHC cbf guys have even figured out how to use a cbr f2 wheel with those forks as well. I am not 100% sure if the cb1100F wheels will fit because the forks are thicker but they may since the cx500 turbo used the same wheel with (I think but can't remember) smaller forks.

as for carbs, the DOHCs used CV carbs and Kehin makes a CR replacement bank but it costs buckets of money. Sudco can also get you them for a SOHC for the same buckets of money. You can use individual VM mukuni carbs but you will need a 4 into 1 cable to acitvate them and a way of feeding each of them with fuel. You will also need to find a way for them to fit the stock carb rubbers. There used to be a way to modify GS750 and KZ900 carb banks to fit (shortening the bank tubes, etc).
 

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quote:
Also, what's this about an Ex500 caliper - I saw this in response to a question about a CB450, is this do-able for a 750?

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EX500 calipers are upgrades for 750 kawi h2s and 500 kawi h1s. The 88-91 ex500 caliper works with a 5 or 5.5mm rotor which is what the first year kz650s used and they bolt on to a kawi 500 h1 wheel. I had suggested them for a cb750 because it would not be hard to turn the cb750 disc down to 5.5mm to work with the ex caliper. I am not sure if the ex500 uses 35mm or 36mm forks since the kawis used both also and you can use the whole ex front end in a kawi triple tree.

so far I have not had a set of ex500 calipers to expirement with to see about adopting to the cb750 front, although I do have all the other parts to do the kawi conversion.
 

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Discussion Starter #5
well shit. That means, of course, that those forks I got for my CB450 aren't going to do shit for me, with the current spoked wheel that I have, and there's no way I'm buying comstars for my bike. crap, crap, crap. to think that everything else looked like such a good fit...

what a learning experience this is...well, I guess I can always send them back to EBay...

EDIT: I guess I should also be clear that this is for my CB450 - I was asking about the carbs because the Sudco kits I see out there for CB450s are 32mm, and I found other newer Mikuni carbs, also in 32mm, though they're not the standard roundslides.

EDIT #2: Fuck this, I am not letting this problem defeat me - I am going to find something that works using the stock CB450 rotors. I'll consider it my contribution to disgruntled CB450 owners everywhere.

What's critical for brake fit - the calipers just need to line up with the rotor, and the rotor has to fit the wheel, and inside the caliper, right?

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Edited by - borzwazie on Jul 11 2007 1:33:35 PM
 

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critical for brake fit:

- the rotor has to be within spec thickness for the calipers.
- the caliper has to be centered on the rotor
- The mount ont he fork leg as to be suffcient enough that the brake caliper does not add additional shearing loads to the mounting ears.
- the rotor has to be a similar diameter as the one the caliper was originally desinged to work for.

The cheater way that chopper guys used to do it was to use one of the wheel spacers and to weld a triangular caliper mount to that, or make one that replaces the spacer and rides on the axle, with a support brace attaching it to the fork legs. Go look at any harley springer font end with a disc brake and you will see what I am talking about. the mount has to be thick since it is a brake mount.

it must be a good way of doing things since modern sport bike radial mount calipers work almost the same way. Doing it this way solves a lot of your problems because the caliper and rotor are now located radially on the same axle. Harleys still use this system so maybe there will be a caliper/bracket you can adapt to your needs.

or you could just put a drum on there and it solves a lot of these other problems.



Edited by - geeto67 on Jul 11 2007 2:16:23 PM
 

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bingo

somewhere in my parts stash I have a magnesium one for a cb750 with the caliper. I'll see if I can snap a pic so you can see.

Edited by - geeto67 on Jul 11 2007 2:29:30 PM
 

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Discussion Starter #10
I wonder where I'd get rotors that would fit my CB450 hub...that looks almost too cool not to try. You wouldn't even need to weld anything, just cut up a bit of sheetmetal...

EDIT: DOH! The whole point of this is that I don't need custom rotors...stupid!

I am going to check this out tonight.


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Edited by - borzwazie on Jul 11 2007 3:37:23 PM
 

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I had a thought about this last night....

what about a 75-76 cb750F suspersport rear brake caliper as a front brake? It already has the axle mount and the discs for the cb750 are pretty close front and rear as are the calpers. Heck you could even shorten the factory strut bar to work with your forks.

wadda think?
 

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Discussion Starter #12
I'd probably need a different wheel hub, wouldn't I? The CB450 hub/rotor probably wouldn't match up there (although I'm pretty sure the spoke pattern would match on 750/450 wheels)...

Would that caliper have enough cojones for a front brake? (not like it probably takes much to out-do the stock CB450 caliper...)

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quote:
I'd probably need a different wheel hub, wouldn't I? The CB450 hub/rotor probably wouldn't match up there (although I'm pretty sure the spoke pattern would match on 750/450 wheels)...

Would that caliper have enough cojones for a front brake? (not like it probably takes much to out-do the stock CB450 caliper...)

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unlike modern bikes where the rear brake is a tiny rotor and small caliper the cb750F uses the same rotor front and rear. I am positive they are the same thickness and diameter (and I am pretty sure they share a part number too). The front caliper and rear caliper are pretty close in size and I am willing to bet it will work as a front (as good as honda front brake works anyway which is not all that great).

here is my stupid question of the day - what wrong with your 450 brakes that you feel the need to upgrade to slightly less inferior parts? I mean, why not just go the full sportbike front end, wheel, and forks and save yourself the hassle? A 750 front caliper is pretty similar to the 450 caliper (same piston) so cb750 parts are not that much of an upgrade. Personally I would try to find cx500 turbo stuff (cb1100F export also) to get those cool gold tri star rims and rock that instead of a comstar. Even the cb1100F rim or the cbr600 f2 rims are cool looking also.
 

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Discussion Starter #15
I don't actually feel any overpowering need to switch calipers - I have a CB450 hub, a nice Akront aluminum rim, and good spokes, and I want to keep those, but I didn't know if just any caliper could be adapted via your excellent example, since I now have different forks that I'm using. I was just scouting stuff out. If the 450 caliper works ok like this (and honestly, I was going to try it first, because, hey, I have one) then there's no need. If it doesn't, then the sportster caliper in my second example can be found really cheap on ebay.

This all started because I'm impatient and something about rust and pitting on the original forks just irked me. Sure, I could just paint them, but it would bother me like an itch I can't scratch. New tubes for the 450 are really expensive, and decent ones on ebay go really fast for more money than I'd like to spend.

Also, I'm sucking your brain dry of information!

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fair enough, try it with the 450 brake setup you have and see how it works. I just suggested the cbF rear caliper because it is already one piece with that axle mount so it would have made your life a little easier.

and my brain could always use the room so suck away.
 
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