CB400 - Twin discs? thoughts

[Integra99]

I wondered if anyone on here had knowledge if a twin disc set up is possible on the CB400f.

I guess its feasable to use another left leg of a cb400f and caliper on the right side? The disc would then be retained using the original bolts, potentially a spacer, I'm already removing the speedo cable as running a GPS speedo..  a brake pipe junction perhaps uprated MS.

Either way I wondered if it had been covered before..  this will be phase 2 of the project but thinking of collecting a few bits.

[K2-K6]

I was trying to think if I'd seen one but don't recall an example.

The fork legs are generally handed on the bigger bikes as far as I know. So if you took two left 400 legs and fitted them,  then the right hand caliper would have to be fitted backwards.

The twin conversions on bigger capacity have the fork legs cast as a mirror image of each other which facilitates their conversion.

Is it how it looks that you're after? Or just straight brake power?
If it's power of braking that's the reason, you can use a different bore mastercylinder to change the leverage. Smaller piston in there changes leverage over the caliper piston to raise the squeeze you can exert.
The disk size and caliper performance aren't as poor as some would indicate. Honda were very conservative with mastercylinder ratios at that time and most newer stuff uses very different spec to reduce the hand pressure required.

[PatM]

agree with this- if brake improvement is required and all other areas have been coved on the standard set-up, then a larger Master Cylinder bore is the preferred option.

I had a Triumph Daytona 995i that had sloppy brakes from new- Triumph even changed the disks! Eventually the bike was given to someone to use as a Track-day hack and the problem was realised by its new pilot!

He changed the master cylinder for a larger bore one and the problems was resolved!

For the sort of riding I do, i find the 400/4 adequate- its never going to lock up in the dry but I have lived with it as it is- Ive had a few 400/4s and one of them had its brake lines replaced for Goodrich hoses- TO BE HONEST- I noticed no difference at all except a hole in the bank account for the job.

i think the 400/4 brake performance, after all the mods are done with stock is a question of what are you comparing it with?

Ive seen 400/4s with twin disc setup from another bike- but i dont know what from? CX500?

It will look odd with the callipers on front/back of legs.

[Laverda Dave]

I've always found the performance of the single disc on the 400/4 adequate.  It was only when I rode a VFR400 with twin discs at a track day I understood how braking power has moved on! It's all relative though and for normal road riding with the performance available from a 400/4 I think a single disc is fine.  If you want real braking fun try riding my Triton with a twin leading shoe front brake, a real cure for constipation in heavy London traffic . I improved its braking performance by fitting of the anchor from HMS Belfast!
I would be careful about adding another 400/4 leg though to the other side, check the casting as the swing arm brake lever may not fit the other way round, there is a long adjuster bolt and spring, this may not be long enough if turned around and the countersink for the adjuster bolt will also be the wrong way round in the swing arm.

[K2-K6]

I can see why you went that way with the Triumph PatM,  my view is the Honda is the opposite and that your hand is at too much of a disadvantage. So I feel the master should be smaller bore.

https://www.apracing.com/product_details/motorcycle/master_cylinders/original_adjustable_ratio_master_cylinder/cp3125_family.aspx

You can get these to play with different leversge ratio,  not quite the same as changing bore size but do similar changes to effort versus travel.

[Tomb]

Its a leverage issue, if you have a large piston M/C travel will be less on the lever but effort required will be higher.
A smaller piston M/C will be easier to work, less effort, but have more movement on the lever, meaning you can exert more pressure at the pads for the same strength hand.

I have improved braking by doing this, and with good hoses and well bled brakes not much travel extra.

The Triumph may have had too much leverage hence needing a bigger M/C.




Tom

[ka-ja]

Honda 400/n or dream will go in the 400/4 yokes

[gtmdriver]

+1 for Tomb.

Pressure  = Force/Area so for a given force:-

Larger diameter master cylinder gives less lever movement but a lower fluid pressure.

Small diameter master cylinder gives more lever movement but a higher fluid pressure.

If you did manage to fit a second disc though you may well have to move to a bigger diameter master cylinder in order to supply fluid to two calipers.

When I decoupled the brakes on my Moto Guzzi I had to fit a 15mm master cylinder in place of the 13mm original.

[Integra99]

Thanks all, yes I agree the single disc does a good job..  and I should probably just leave it as is.. but I do a lot of track days and the 400/4 brakes are quite a shock to the system but its mostly about looks and the challenge being a custom bike.

The 400n Superdream looks a potential donor, I think even 31mm forks?

I need to investigate that option first I think.. it really will be a phase 2 part of the project though as said in the replies its plenty adequate for now but will be on wish list list.. as for the M/C very useful and it explains why my old M/S on my XS750 struggled with the 4 pot calipers I fitted originally, Now running an R6 front end.

[ka-ja]

Hi,
    CB400/4 forks tubes are 33mm dia. the same as the 400 superdream, as with  all old bits, getting stuff in good condition is a headache, and staying with spoked wheels instead of superdream comstars is expensive, but the braking is much improved, especially in the wet.

[Integra99]

Thank you.. Ka -Ja, yes I've looked online already but just very poor condition units.. it will be a phase 2 next step on the bike so will keep an eye out there!