Topic: CB400f Rear Disc

[Stevevo8]

Looking to convert my CB400 to rear disc.

Does anyone have any idea of which hub I can use?

[754]

Use Yamaha mags, your front disc will bolt on. actually on the front you will have choice of Yam Honda, Ducati disc, you will have to mod a lot to run bigger rotors. Yam mags are reasonable price, 400 Yam may be a good choice.

 Honda front hub off 750 or 500 or 450, with a spacer will work to build a disc wheel, and take Honda rotors, you may have to run solid sprocket..

[brandon]

OP, I have a 400f too and I've been obsessing on how to do this as well! Though, I don't have much to add in the form of any technical knowledge aside from the right wheel/hub/disc combo, do you have any thoughts on how you will mount the caliper and master cylinder?

Today I was looking at a modern street bike, and the bracket to hold the master cylinder was made into the right side rear set and was all one piece.

[fasturd]

Look at my build thread, my 400 has a Brembo/EPM rear disc kit on it.

Wouldnt be that hard to do after looking at how simple this kit is.

Hard part is finding a suitable wheel. You wont be able to use the stock 400 obviously. But there are many vintage mag kits out there. Hayashi, Lester, Morris, EPM and they all have different adapter set ups.

[Stevevo8]

Looking to run a spoke wheel in the rear. will Any year 750 any specific model work?

I already converted the front to a GSXR front end

[Industrial Cafe]

the cb750 F1 had a spoke wheel with a disc, and member fishhead makes a real good lookin rear disc setup.
http://www.fishheadbigbrakes.com/

[JZEROE]

I'm generally all for modding the piss out of your bike, but I have a 400F, and have never run into a problem with the rear drum. And I live and ride in San Francisco—the land that eats brakes. Actually, I find it almost too easy to lock the rear up as is. Why not take the money you were going to spend on a rear disc and buy a sweet-ass cafe seat. Or an overbore kit. Or a fork brace for the front. You know, something the bike actually needs to increase its levels of ass-kickery. Just an opinion.

[Industrial Cafe]

I lock mine up all the time too.
    but I think a 10-12 inch disc in the back is a much more efficient rear brake than a 7 inch drum. drums lock up too easy.
(and it looks bad ass)

[754]

 I sort of like the look of smaller modern style rear brakes, shows off the wheel better..

[Industrial Cafe]

yeah, that's true, but it's not as "ZOMG-race bike" as an enormous rotor in the back

[fishhead]

   I like mounting the caliper on the bottom of the disc as it shows off the wheel more. Most people are expecting to see a top mounted caliper on the older bikes and when its not there where they expect it to be, they tend to look harder.

 The same brake/bike as what IC posted, just finished. His pic of it was in the prototype stage.

[brandon]

This bottom mounted caliper seems more prone to being damaged. Also, aren't most all calipers on modern bikes positioned around 2-3 O'clock (looking from the right side) to generate downward forces to help keep the rear end from lifting, by using the spin weight/cintrifical force generated by the rear wheel?

[Industrial Cafe]

no.

[Industrial Cafe]

let me rephrase that.

Benefits include:
  (1) moving the weight down to lower the center of gravity(not super amazing, but every little bit helps)
  (2) It looks bad ass  (yes, that is important)
  (3) Less of a chance for rear wheel lockup (cause I said so, do not question my speculatory wisdom!!)
  (4) It looks bad ass (yes it does)



I don't know if the 2 'O'clock positioning of the caliper has much of an advantage over the underslung caliper.
   If it did, Brembo wouldn't make underslung caliper upgrade kits for most bikes.

[754]

Why stop there.. pun intende..

 ..if you really want bad ass points, run a Sproter on the left, and nothing on the right..

.. If you want to look bad ass X 3, run a 12 spoke American, or an ET spoked 15 with a Sproter..

[Industrial Cafe]

sprotors are expensive, but they sure are neat.

[754]

Ok then, run a disc inboard of sprocket, perimeter brake, or jackshaft with brake...

[fishhead]

The main purpose of the rear caliper is to stop the wheel from spinning, regardless of where the caliper is mounted. Mounting the caliper at the 2-3 O'clock position wont give it any anti-dive properties.

 Mounting the caliper at 2-3 O'clock may keep it from getting damaged in a fall. With my caliper mounted low, I would need to grind away most of my muffler and some of my axle before it would hit in a fall over.
  The lower mounted caliper lowers the center of gravity on the un-sprung weight of the rear wheel and improves handling.

 To complete the bad ass look, put 330mm discs and 6 piston calipers on the front.

[brandon]

Hmm. Interesting. So basically there are no other beneficial physical properties to having the rear caliper at 2-3 o' clock? I'm curious as to why just about every motorcycle racing team hasn't moved the placement of the rear caliper to 6 o' clock position if it lowers the center of gravity enough to even give it mention?

Observation tells me that they wouldn't because the caliper is more prone to damage from road debri and water damage, ease of maintanence and I'm going to go out on a limb here again, to say that the unsprung weight of the rear wheel helps to 'push' down on the caliper and control arm to help keep as much rubber in contact with the pavent as possible, since hard braking causes a shift in mass forcing the rear to unload and the front to preload.

I wish I could find data on this and I'm looking , but for now I simply don't buy the 'low center of gravity' statements as being that critical.

[754]

You can.. inspect/change pads/ bleed... quicker on top, that may be it...

[Industrial Cafe]

Hmm. Interesting. So basically there are no other beneficial physical properties to having the rear caliper at 2-3 o' clock? I'm curious as to why just about every motorcycle racing team hasn't moved the placement of the rear caliper to 6 o' clock position if it lowers the center of gravity enough to even give it mention?

Observation tells me that they wouldn't because the caliper is more prone to damage from road debri and water damage, ease of maintanence and I'm going to go out on a limb here again, to say that the unsprung weight of the rear wheel helps to 'push' down on the caliper and control arm to help keep as much rubber in contact with the pavent as possible, since hard braking causes a shift in mass forcing the rear to unload and the front to preload.

I wish I could find data on this and I'm looking , but for now I simply don't buy the 'low center of gravity' statements as being that critical.

don't try to over analyze it man, it just looks cool.
  I didn't extend my swing arm for any functional reason, I just thought it looked cool.

[fasturd]

I have a set of those 6 pot Tokikos just waiting for the right project...

I agree with two of the above posts. First of all the stock rear brake if functioning normal is just fine on a 400.

Second, I totally agree discs look super cool. Which is why I had to have one on my latest project.

Third. Its all good!!!!

[srook]

Triumph used an underslung rear caliper on the 1976 Bonneville.  They changed the position to 11 o'clock 4 years later on the 1980 models.  The reason was the caliper was prone to collecting water and debris if used in the wet.  On the Triumph the rear caliper had to actually be moved to bleed it because of its positionioning the bleeder was not at the high point.  Also they had a run on warranty claims for rear calipers during those years.
Scott

[Joel]

Where is the frame mount for the caliper locating rod usually placed?

[fasturd]

On my EPM/Brembo kit it uses the original barake arm.

[brandon]

Hey Industrial, I'm not here to step on toes. I'm only curious and learn through asking. I think the 6 o' clock caliper looks good too, but my needs are different than yours and that's part of what our bikes different from one-another. If I came across as being pesky, I'll tell you those were not my intentions

Now back to converting to rear disc!

[Industrial Cafe]

you're not stepping on any toes, I'm just messing with you.
I always forget that text doesn't transfer sarcasm.


EDIT: I should put this in when I do that-

[Industrial Cafe]

I just read a few articles on the braking setup of F1 cars vs passenger cars.

the reason they put the calipers on the bottom of F1 cars is heat dissipation (heat goes up) and the center of gravity, because everything on those cars has to have the lowest possible COG.

[Stevevo8]

I found a rear hub from a CB750f, could this possibly work?

[Industrial Cafe]

try it and let us know.

I think the axle is a different size, so you'll either have to swap swing arms or change the bearings

[Stevevo8]

Im looking at it from teh width stand point. Changing bearings might be the easiest part of the whole deal.

[Industrial Cafe]

if it's too wide, cut some off. there's always a good amount of spacers in there anyways.

[Stevevo8]

Im on it, its gonna be cheaper finding out this way than buying a talon hub.