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Author Topic: Twin Piston Brake Upgrade Using OEM parts For CB750F  (Read 38685 times)

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Offline RAF122S

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #100 on: February 23, 2017, 09:49:59 pm »
Geeto,  very nice cb750k (79-82)! Is it yours?
David
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Offline Geeto67

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #101 on: February 24, 2017, 04:33:49 am »
No it's just a pic I pulled of the internet. I did own a 79 cb750 anniversary edition once, it was a pretty good bike.
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Offline scottly

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #102 on: May 13, 2017, 07:44:00 pm »
I don't know of any fully "bolt on" ways to mount a wire wheel in mag wheel forks.

I know of one way, but you lose the dual disc. There is a model of 1979-1982 cb750K bike that uses a wire wheel compatible with the dual piston caliper:



the problem is that the backside of the wheel doesn't have a surface to mount a disc even if you drilled through the wheel:



So if you had a K bike with a single brake and you wanted to upgrade to a better single brake without losing a wire wheel you could use a 1977-78 F front end (Forks, trees, axle, etc), the left side 1981-82 dual piston caliper, and this 79-82 cb750K wire wheel and spacers and (might have to mix and match spacers with 77-78F setup) and end up with better braking. Is it as good as dual discs? no I don't think so, but it is better than a swing caliper single puck.


and just to give you an idea as to how rare this wheel is, these are the only models that used this front wheel that is compatible with the later dual piston caliper:

    1979 CB750K A - FRONT WHEEL
    1980 CB650 A - FRONT WHEEL
    1980 CB750K A - FRONT WHEEL
    1981 CB650 A - FRONT WHEEL
    1981 CB750K A - FRONT WHEEL
    1982 CB650 A - FRONT WHEEL
    1982 CB750K A - FRONT WHEEL
What is the diameter of the F disc? 550 discs are 275mm, and bolt right on to a 750K/early F spoke wheel.
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Offline Geeto67

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #103 on: May 15, 2017, 08:18:12 am »

What is the diameter of the F disc? 550 discs are 275mm, and bolt right on to a 750K/early F spoke wheel.

ok...but are they 5 lug or 6? If they bolt to an early K wheel they are 6 and not compatible with the 77-78 type of braking system we are talking about here. the 1980-82 SOHC 650 uses a lot of the same parts as the 1977-78 SOHC 750F bikes and the 1979-1980 DOHC bikes. There is no interchange with the earlier bikes without changing the forks and the wheel.
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Offline scottly

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #104 on: May 15, 2017, 07:40:07 pm »
I'm talking about the feasibility of using 275mm 6 bolt rotors with a 6 bolt 750K wheel (in my case a Morris wheel), with the F2/3 forks and the later twin piston calipers, instead of the Comstar or 5 bolt spoke wheel. Why wouldn't the combination be compatible? If the 550 rotors are too thick, they can be thinned. The K hub mounts the right side rotor inboard by about 3mm, which can be corrected with spacers. What is the outside measurement across the F2/3 rotors? 
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Offline seanbarney41

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #105 on: May 15, 2017, 07:48:23 pm »
the f2/3 rotor carriers are dished outward quite a bit(no, I don't have measurements)
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Offline scottly

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #106 on: May 16, 2017, 07:13:55 pm »
Sean, a quick check with a tape measure is close enough for now; if it's close to 5", the spoke wheel swap may work. TIA.
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Offline seanbarney41

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #107 on: May 16, 2017, 07:22:15 pm »
Sean, a quick check with a tape measure is close enough for now; if it's close to 5", the spoke wheel swap may work. TIA.
ok, I will try to grab a tape measure soon....however, I am of the opinion that, like a handycapped child, owners of comstars really just need to learn to love them.  They are special. lol
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Offline scottly

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #108 on: May 16, 2017, 07:32:01 pm »
I don't have comstars, I just want better brakes! ;D ;D
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Offline jaguar

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #109 on: May 17, 2017, 11:20:51 am »
IF anyone is looking for a "kit" to do this swap feel free to PM me.
Have some parts "in stock"

Thanks

Offline seanbarney41

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #110 on: May 17, 2017, 01:00:58 pm »
IF anyone is looking for a "kit" to do this swap feel free to PM me.
Have some parts "in stock"

Thanks

jag, that would be super convenient not to be searching eBay for bits...if you are not looking for top dollar.  I will pm later.
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Offline scottly

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #111 on: May 17, 2017, 07:50:16 pm »
Did you find your tape measure yet, Sean?
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Offline seanbarney41

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #112 on: May 17, 2017, 07:59:59 pm »
Did you find your tape measure yet, Sean?
lol, do got tape measure!  Now, I must find the key to the garage!
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Offline jaguar

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #113 on: May 18, 2017, 03:38:28 am »
I collect the arts from time to time.
Unsure if people would be interested in just the used parts, or would prefer them all freshly rebuilt and PC black.

Offline Geeto67

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #114 on: May 19, 2017, 08:40:44 am »
I'm talking about the feasibility of using 275mm 6 bolt rotors with a 6 bolt 750K wheel (in my case a Morris wheel), with the F2/3 forks and the later twin piston calipers, instead of the Comstar or 5 bolt spoke wheel. Why wouldn't the combination be compatible? If the 550 rotors are too thick, they can be thinned. The K hub mounts the right side rotor inboard by about 3mm, which can be corrected with spacers. What is the outside measurement across the F2/3 rotors? 

The 6 bolt rotors are stainless steel, it's quite a bit of work to "thin" them, but you are right it's possible. However, thickness isn't really a problem unless there is dragging at rest (which I don't think there is). It does cut down on the braking feel range because the piston has to travel less to fully lock the wheel, but not something drastic.

If you have a morris 6 bolt wheel, why not try and find a 5 bolt wheel instead? They made them and they are out there.

For the amount of work you are doing to keep a spoked wheel, can I make a different suggestion? What about changing the front end entirely? GL1000 swap is popular and common.

you could get an early kz550 spoke wheel front end and do an ex500/ zx6 caliper conversion. Still a spoke wheel, 5.5mm discs, 36mm forks instead of 35mm, as much aftermarket support.

If you have single disc right now, you could just do the single disc DOHC spoke wheel upgrade. It's one of the dual piston calipers and rotors on a spoke wheel - will still look close to stock and be better than the single puck brake, it just won't be as good as dual discs.
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Offline Geeto67

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #115 on: May 19, 2017, 11:46:27 am »
I just had a thought....but you might not like it.

 EBC makes new brake rotors for the CB750 in both 6 lug and 5 lug bolt pattern (under the Pro-Lite brand). You could have them make you a 77-78 CBF rotor drilled for the 6 bolt pattern to bolt to your K7 wheel.

Why you won't like it? off the shelf rotors are about $200 per rotor and custom work would probably be more expensive. So that's $400-500 in rotors to make your swap a bolt on, not counting what you pay for forks and calipers.

maybe you can get an undrilled blank and do it yourself, but I don't know if that will bring the price down.
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Offline jaguar

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #116 on: May 19, 2017, 11:49:45 am »
Those rotors always look so nice though.
Wonder how they perform.


BTW
I have two sets of cores for a caliper swap if anyone is interested.

Offline scottly

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #117 on: May 19, 2017, 11:55:46 am »
The Morris wheel is a direct replacement for the 750 wire spoke wheel, so if this works with the Morris, it will work with the Honda wheel. A fork swap opens up a whole can of worms; at one time I had a complete Kawi 550 front end on the bike, including the Morris clone wheel, but the lack of off-set in the triples meant I had to severely limit the turning radius to keep the fork tubes from bashing into the Seeley tank. It would be much easier to slip F2-3 fork tubes into the K7 triples. There are several places that can thin the rotors. If someone could please measure the width across the F2-3 rotors, I can tell if it will work or not. ;) 
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Offline scottly

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #118 on: May 21, 2017, 09:38:07 pm »
A K7 wire spoke wheel with two rotors is just under 5". If the F2/3 is similar, the spoke wheel should work. As far as the thickness of the early rotors, the twin piston bracket has an 8mm "slot" where it fits over the rotor; since the early rotors are 7mm, the bracket would need to be exactly centered over the rotor to give a .5mm (.020") clearance on both sides. Godferry's Garage (Jeff) will sell a drilled and thinned rotor for $88 with a core, or $124 outright.
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Offline Geeto67

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #119 on: May 23, 2017, 10:57:00 am »
just to be clear, you need the measurement from the outer face of the F2/F3 right disc to the outer face of the Left disc?

I just got my 1978 F moved to my place on sunday, I'll try to grab a measurement.
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Offline scottly

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #120 on: May 23, 2017, 05:52:34 pm »
Yes, that is the measurement I need. Thanks!
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Offline seanbarney41

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #121 on: May 25, 2017, 10:46:39 pm »
still not seeing how this can work, here is pics and measurement anyway...outside to outside woodworker style
KIMG0146 by Sean Barney, on Flickr
note how offset these discs are compared to non 77/78f sohc discs...this is why I don't see how it can work practically
KIMG0147 by Sean Barney, on Flickr
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Offline scottly

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #122 on: May 25, 2017, 11:19:33 pm »
Yup, the spoke wheel should work. ;D What is the actual measurement; it's hard to tell in the pics? 5 3/16? Thanks!!
« Last Edit: May 25, 2017, 11:22:43 pm by scottly »
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Offline seanbarney41

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #123 on: May 25, 2017, 11:22:01 pm »
5 1/4" outside to outside
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Offline seanbarney41

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Re: Twin Piston Brake Upgrade Using OEM parts For CB750F
« Reply #124 on: May 25, 2017, 11:23:31 pm »
measurements taken from completely bone stock cb750f3 frontend
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