Topic: cb400f dual disc conversion

[setdog]

Hi all, ive now got a 75 cb400f, its a total mess, all body parts missing so I plan a cafe restored mod. 

Naturally I want to do a dual disc front end conversion.  And while there is a lot of info avail its still
A bit confusing trying to piece it all together. 

The DCC guys say they used a combination of cb400f 450 750 and fzy(?) Parts, and I've
Tried to contact them for more details. 

If youre familiar and have some pointers, I'd appreciate your help. 
I'm not really equipped to do much machine work, so I'm looking for a suitable bolt on type
Of solution, if that's even possible.

[calj737]

It would appear from pics that the right fork has the same mounting bosses as the left. If so, the addition of another factory caliper, mounting arm, and disc is the bulk of needed parts.

You will end up needing to deal with the speedo gear(probably lose it) and you will need a new wheel spacer to adjust the gap remaining. Of course, longer rotor mounting bolts and a master cylinder to support the dual brakes/lines.

This approach is most commonly used with these bikes. Have the 2 rotors drilled to lighten the added weight.

[Matt Chapter]

Naturally I want to do a dual disc front end conversion. 

Have you ridden the bike?  It's always interesting to me that people would want to modify a 40 year old bike, throw parts, time, and money at something like this without an understanding of what the current performance is.

Sure, in its current state it probably doesn't stop well, but there's a litany of fixes you need first, before doing dual disc.  Think master cylinder rebuild, new lines, rebuild the caliper..  perhaps even refresh the rotor you have.  Remember this bike makes less than 40 hp stock.. Stopping it isn't that hard, and in fact with my stock front brakes, with original pads, (!!) I can get the rear wheel quite light.

That being said, if you do ditch the speedo gear, I'd be interested.

[Tim2005]

It would appear from pics that the right fork has the same mounting bosses as the left. If so, the addition of another factory caliper, mounting arm, and disc is the bulk of needed parts.

Alas, the stock 400f forks don't have those bosses on the right leg. There was a right leg with bosses available in the race kit/ RSC parts but it is very rare.


As per Matt's advice there's some doubt as to whether twin discs are really needed on a 400, especially with modern semi-sintered pads,  but if you do want to try it you can check out this thread http://forums.sohc4.net/index.php?topic=103463.0  and also this page https://web.archive.org/web/20091226042822/http://cafe400f.cloud.prohosting.com/html/CB400f_Dual_Disk_Project.htm    - actually now archived, this was written a few years back a by a guy called Jeff Chenevert and is a really good guide,  (though if you do try to follow it beware that you actually need to buy a new 40 hole 18" rim, you can't use the 400f's one on the 550 hub as it suggests)

[Powderman]

Having a second disc isn't really an improvement if everything else is vintage. I also wanted the second disc but also craved better handling and better tire capability. It was for these reasons that I went one step further and did a complete front end swap. I also wanted mag wheels and to delete the spoke wheels so I went with a full CBR600F1 front end and rear wheel. The rear needed a bunch of machine work to make it work, but the front was nothing more than an ALLBALLSRACING bearing swap kit. I shopped around and came up wit the full front end parts for around $300.

 

[calj737]

You asked for some pointers, but you didn't indicate whether a modern for swap was part of your goal. Powderman is right (he usually is from every time I've seen him respond) a dual disc where everything else is "stock" is probably not needed. If you want he modern front end with USD forks, then you have some machining to do, either on the front or the rear.

If, like Powderman you use modern forks and mags, a donor bike is cheapest route. BUT, the front is simple, the rear is a bear if you don't have much experience or access to machinist buddies.

If you want modern forks and dual discs, but stay with spoke, then custom front hub, caliper brackets, spacers for the front are required, and the rear can stay "stock" with drum unit. It's a coin flip (front end or rear end custom machining).

If you are chasing a "look" drill your rotor, do a complete brake system rebuild, SS lines and your safety is very comfortably in hand. Everything else becomes involved and expensive. It's all achievable, but make sure you weigh the costs against the goal.

Lots of people and proof examples to help you on the way, but nothing you are describing outside of my first recommendation is "bolt on".

[alacrity]

It's all about trade-offs imho.  Are you going to be riding in such a way that you will need to STOP RIGHT F'ing NOW FROM 100mph? Often? Then maybe... and only MAYBE...  a dual disk setup could be useful.

Here's why you don't want one:
DOUBLE the unsprung weight in the front will be seriously detrimental to handling.  These bikes have thin necks and trees and flexi frames.  Add all that heavy metal way down at the end of the 35mm fork tubes and youre gonna get crappy handling.  This is as much a safety issue as a performance issue.

You can VASTLY improve your braking by properly ebuilding or replacing the master cylinder and throwing away the spongey stock rubber brake lines. Replace em with new stainless steel lines. Of course you need to bleed the system meticulously.  I did this on my cb500, and because it was all fresh and/or completely renewed parts, I switched to Dot5 for heat control and "doesn't eat paint when you spill it" properties.  I have WAY more brakes than I need now with two fingers I can lock the front end -- and I have pretty good avon tires on it.

[setdog]

Guys, I DO greatly appreciate these notes.  This is my third bike in a year, and I
Still don't have much experience in terms of performance.  Well I really don't have any.

Its easy to get lost in other peoples builds, and some of the sexy looking
Mods out there. 

Sounds like the best course is to first rebuild the bike to stock specs before
Getting carried away.