Topic: CB400F Dual Front Disc with 2 piston floating Calipers

[blight]

Hello,

I'm the new guy here, and wanted to share an idea I had for my 1976 CB400F. As you know, the front single (10"?) single rotor disc is awful.

I bought a brand new CB400F in 1975, and it seemed OK back then, but then I was just comparing it to period drum brake bikes I had before it.

My current one is a 1976 CB400F, and I recently dragged it out of storage and started a thorough cleanup and refurbishment.

Amazing what time will do to what was a pretty nice bike, even when parked under a highly protective bed-sheet for 12 yrs!

Anyway, new caliper body, SS piston, new seal, rebuilt master cylinder, flushed line, new pads, de-glazed rotor.... sure it stops.... eventually, and it squeals like a stuck pig. Yep, it's a crappy disc brake design.

So... one of my other project bikes is a VT500 (Ascot) cafe bike that I retrofit with a VF500 Interceptor Fork (37mm) with dual 2-piston calipers. Yes, those fork sliders were Honda red in a previous life... I stripped and polished them.

The fork has the ATAC anti-dive as well, and seems to be a nicer fork than the CB400F in terms of damping and rigidity.

For the wheel, I used a CB400F hub, and mounted two 4-bolt CB400F rotors to it.

They are the correct diameter to match the VF500F rotor OD!

I laced up a new shouldered Akront 18" rim to the CB400F hub using SS spoke & nipple kit from Buchanan... they are ACE!

After mounting the new tire and balancing it, I put it on the bike and the stopping power is very nice!

Drilling the rotors could help too with disc and pad glazing and stop the squealing... by the way, I have zero squealing on the 2 piston caliper setup.

The VT500 makes ~10hp more than the CB400, so it's a good idea to be able to haul it down from 'high speed.'

My question is this... why wouldn't this setup work with a CB400F, if you swapped in the VF500 triple-trees and figured out a bar arrangement?

Pretty sure you could use the stock 18" CB400F wheel-hub assy.

Here's what it looks like on my VT500 Ascot cafe project:










Comments?

Cheers,
BLIGHT

[knowsnothing]

Welcome my friend  .  First off let me say that Ascot came out stunning, solid work.

I have a few cb350f/cb400s and have been looking for a easyish brake upgrade  because the ones they have are pretty rubbish.

I don't see why your idea would'nt work, but i have a few questions. 

1)Which triple are you using on the ascot?  Is it from the ascot or the vf500?

2) What did you use for wheel spacers?  Are they oem or custom.

The biggest issue i see is stock 400 forks are 33mm, so a different triple is required to fit the 37mm vf500 forks.  If you were to use whichever triple you used on the ascot, then the next questions becomes will the stem work (length/bearings) with the 400 frame or will you need change it for one that will.

Either way, i find this intriguing

[blight]

Welcome my friend  .  First off let me say that Ascot came out stunning, solid work.

I have a few cb350f/cb400s and have been looking for a easyish brake upgrade  because the ones they have are pretty rubbish.

I don't see why your idea would'nt work, but i have a few questions. 

1)Which triple are you using on the ascot?  Is it from the ascot or the vf500?

2) What did you use for wheel spacers?  Are they oem or custom.

The biggest issue I see is stock 400 forks are 33mm, so a different triple is required to fit the 37mm vf500 forks.  If you were to use whichever triple you used on the ascot, then the next questions becomes will the stem work (length/bearings) with the 400 frame or will you need change it for one that will.

Either way, i find this intriguing

Hello! Thanks, the VT is a fun little bike and it was a challenging project.

I used the 37mm VF500F Interceptor fork tubes and sliders, and VT500 stock 37mm Ascot upper and lower triple clamps.

They are a little wider apart than the CB400F (like 1/2") so IIRC used a the axle from the VT or VF500, which is longer and fit the wheel bearings on the CB400F hub. At least that's as much as I can remember. Maybe I needed different bearings? I don't think so.

Also, the VT500 upper and lower triples are ~9" apart vertically (longer steering stem) whereas the CB400F are ~7.5" apart vertically.

I'm thinking the 82' XL500 triple clamps would be about perfect, as they are 37mm tubes too, but are they the right stem length and spacings? Interestingly, it has a clamp securing the central steering tube, so it looks like it's removable like the fork tubes!

Dunno, don't have one to play around with... maybe someone here has some basic dimensions: tube center/center, and upper to lower spacing? Maybe I can find one cheap on ebay as a starting point.

I have a CB750 SOHC in the garage and did a coupla quick measurements and it could work, but the steering stem looks to be probably too long.

I would need to get some pieces together and do a test fit on the CB400F.

It's surprising how much interchange of parts there can be between various models from the same maker.

I'm not gonna do this right away... still working on getting the CB400F cleaned up and rideable. Here's a pic, she's a good 10 footer:



The VF500 fork tubes are longer than the CB400 because the VF used clip-ons, so they stick up above the upper triple a couple of inches.

The Ascot is wearing no gaitors these days... just the sliding Ceriani-style dust boots.

Here's a list of other 37mm forked Hondas for reference:

CR-80R (96-98)
CR-80R (99-02)
CR-85R (03-04)
CR-125R “Elsinore” (79)
CR-125R “Elsinore” (79)
CR-125R “Elsinore” (80)
CR-125R “Elsinore” (80)
CR-250R “Elsinore” (78-80)
CR-250R “Elsinore” (78-80)
NX-250 (88-90)
XR-250R (81-82)
CMX-450C (86-87)
CX-500TC (82)
FT-500 “Ascot” (82-83)
VT-500 "Ascot" (83-84)
VF-500C “Magna” (84-85)
VT-500C “Shadow” (83-84)
VT-500C “Shadow” (85-86)
XL-500R (82)
CB-550SC (83)
CBR-600F “Hurricane” (87-90)
CB-650SC “Nighthawk 650” (82)
CX-650T “Turbo” (83)
VF-700C “Magna” (84)
VFR-700F “Interceptor” (86)
CB-750F (81-82)
VF-750C “V45 Magna” (82-83)
VF-750S “Sabre” (82-83)
VFR-750F “Interceptor 750” (86)
CB-900C “Custom” (80-82)
GL-1000/K “Goldwing” (75-79)
GL-1000/K “Goldwing” (75-79)

Cheers,
BLIGHT

[blight]

On second thought, I don't think this is the right choice for a brake and fork upgrade on the 1st gen CB400F.

The VF500 sliders are about 1.5" too long visually for me if you were to place them on the CB400F.

I could take the time to take a current photo of the VT500 and PhotoShop it onto the CB400F, but I think it's not gonna look right.

The fork dust-caps will just be too high above the fender in order to maintain the original styling of the classic CB400F.

It is what it is on the VT500 cafe project bike, and actually looks good, (even has 18" wheel like the CB400F)... but anything goes in that regard on the Ascot Cafe, as it's truly a 'one-off'.

And it's particularly far different than the 'chopper-esque' forks on the original VT500 Ascot (yes, that's the same bike before I attacked it in the rather fugly pic below):



I'll come up with a better looking dual-disc solution for the CB400F, now since I own TWO!

Just bought a verrrry nice yellow 1975 model today!! (Update... It's a 1976)

BLIGHT

 

[blight]

OK guys... glad the SOHC cam Forum is back up! It was down all day it seemed....like forever!

So... I did some measuring today and came up with a plan.

I did order and receive a red 37mm VF500F Interceptor fork with ATAC assy this week... looks nice!

Now... to figure out the brakes, rotors, hub, wheel, spacers, etc to make it work on a CB400F!

Ordered a set of brake calipers and a second rotor too, all courtesy of wonderful ebay.

I ordered an upper and lower triple clamp set for a 1981 CB750F, as it is also 37mm, and looked pretty similar to the CB400F in terms of attachments for gauges, etc.

Here's a pretty crappy PhotoShopped image with the dual-piston, dual rotor setup on the CB400F.

Not the look I really want, but I need real stopping power and a bit less fork flex!

There are a whole lotta imbecile deer and crappy drivers around here, so I need to stop when necessary.



Sorry, that image shows a GB500 seat floating over the CB400 seat... just playing around a bit.

I have a pristine GB500 seat over in my storage unit... gonna go visit there and pick some parts!!

It was cheap enough, and if it doesn't work, out I can always resell all this stuff on ebay if necessary.

I may just swipe the polished forks from my VT500 Ascot project and fit them up to the CB400F with the 1981 CB750F 37mm triples.... just a better fit for gauge mounts, etc.

The reason I'm not using the VF500F triple clamps is due to the fact they have no 7/8" handlebar mounts.

Cheers,

BLIGHT

[scottly]

Hi Blight. There may be an easier, bolt-on solution to improve the 400 front brake. The 550 has a shorter steering stem than the 750. I have not measured, but it may be the same as the 400. If it fits, you could slide 750 F2-F3 35mm fork tubes into the 550 trees, and use the twin piston FT/VT500 style calipers. The front Ascot calipers were 30mm, but there was a larger 32mm version. I have upgraded my FT500 to a 32mm caliper, and am running a single 32mm caliper with a 320mm Ducati rotor on the front of my 750, using the F2/F3 38mm forks.

[blight]

Hi Blight. There may be an easier, bolt-on solution to improve the 400 front brake. The 550 has a shorter steering stem than the 750. I have not measured, but it may be the same as the 400. If it fits, you could slide 750 F2-F3 35mm fork tubes into the 550 trees, and use the twin piston FT/VT500 style calipers. The front Ascot calipers were 30mm, but there was a larger 32mm version. I have upgraded my FT500 to a 32mm caliper, and am running a single 32mm caliper with a 320mm Ducati rotor on the front of my 750, using the F2/F3 38mm forks.

Hello, that's a good idea! I was trying to upsize the fork tubes too, because 35mm is pretty flexy.

I got some triple-tree parts already, but they are not working out yet for various reasons.

I'm now going to drill a used 400F rotor I got on ebay with one of the patterns I saw here in this forum, or draw up one of my own to scale using AutoCAD.

If that stops the glazing and squealing I'll be 'OK' with that for now, even with the single-piston caliper.

LAst night, I did test-fit one of the twin-piston VF500 calipers I got on ebay (non TRAC side) on the rear of the left CB400F fork leg, and it seems to clear the spokes (important!) and could be mounted with a custom bracket possibly, utilizing the mounts on the left leg.

These calipers 'float' on two greased pins, and as the pads wear, both static and piston sides move closer together.

I'll have to look at it again to see if it's feasible and a safe way to proceed.

Can't be any worse than it is right now... with all new parts it squeals horribly (at least not sticking!) and I could stop better if I dragged my feet.

More later...
Cheers
BLIGHT 

[knowsnothing]

Hey Blight some more food for thought, I started going another direction (sorry for the #$%*ty pictures, basement is dark)

Turns out early (87-88 i think) Kawasaki ninja ex500 front end is a pretty good fit in a 350f frame.  Only thing required was purchasing the correct bearings.  Matching rear wheel is a drum, which is nice, and the wheel fits in the swing arm fine. 

Potential downsides are its only a single caliper (but much better twin piston), the wheel size is weird (16inch and thiccc), the rear wheel and/or brake plate will need a little shaving to  center the wheel and line up with engine/front sprocket.  Custom spacers will also need to be make for the rear as well, but I think it is all doable. 

The swap seems to make the bike feel a little squattier , but I think it looks interesting and fun.  This will be my next project once i finish my current cb750k build. 

[blight]

Hey Blight some more food for thought, I started going another direction (sorry for the #$%*ty pictures, basement is dark)

Turns out early (87-88 i think) Kawasaki ninja ex500 front end is a pretty good fit in a 350f frame.  Only thing required was purchasing the correct bearings.  Matching rear wheel is a drum, which is nice, and the wheel fits in the swing arm fine....

Hey, thanks for the pics...for me, just I prefer 'old-school' wire spokes and chrome rims on my CB400F and other SOHC 4's, but hopefully you end up with something you like!

A couple of days ago, I took a pic of the VF500 2-piston caliper just positioned in the same location as the single-puck caliper. It fits the space and clears the spokes on the inside.



However, fabricating a bracket to mount it properly on a CB400F is pretty dodgy, so I think I'm back to a fork swap like I did on the VT500 (black bike) and using a double 400F disc on the stock wheel and hub, with dual twin piston calipers.

By the way, I just picked up another '76 CB400F yesterday (parakeet yellow), and it's NICE. Took it for a ride, and the front brake is way better than my other bike that I've been whining about. I think I could actually stop if a car pulls out in front of me! Well, I like to think so anyway.

Still, I think the VF500F fork swap will be a big upgrade and will look pretty factory, I hope! It will also have TRAC anti-dive, 37mm tubes, and less flexy.

I wish there was a way to get floating rotors on this setup 

BLIGHT

[rupaulpierce]

Front brake isn’t bad with stainless lines, slightly larger MC, and drilled rotor!


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[scottly]

No, if you keep the stock front brake, but want increased performance you need a SMALLER MC. The stock MC is 14mm, same as the 550 and 750K, which is too large for a 38mm caliper. A 12mm MC should give better braking.

[rupaulpierce]

No, if you keep the stock front brake, but want increased performance you need a SMALLER MC. The stock MC is 14mm, same as the 550 and 750K, which is too large for a 38mm caliper. A 12mm MC should give better braking.

You’re absolutely right. I went with a 1/2in, which is 12.7mm... slightly smaller!


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[blight]

No, if you keep the stock front brake, but want increased performance you need a SMALLER MC. The stock MC is 14mm, same as the 550 and 750K, which is too large for a 38mm caliper. A 12mm MC should give better braking.

You’re absolutely right. I went with a 1/2in, which is 12.7mm... slightly smaller!
Sent from my iPhone using Tapatalk

Good info guys... thanks! I'll look into that option, and the drilling too... it can't help but to keep the pads from glazing over, which they do. I think the open areas will act to scrape the pads just so slightly, and keep them somewhat more grippy-erish.

Oh... and Venhill black braided line to the front caliper(s).

BLIGHT

[blight]

Hello folks!

I have been sorta... well, really kind of busy trying to sort out this CB400F weak front brake!

I have some great results finally! At least for this 1st attempt.

I arduously searched the internet for a 33mm Honda front fork with a proper back-side caliper mount (not like the pivoting, front mount) and found the 33mm CM400 fork would work, with minimal mods.

Well, minimal mods in my opinion anyway!

I installed the CM400 front fork and then modified the CM400 axle to work with the CB400 hub.

It's a really LONG story, but the CM400 has a a single piston like the CB400F (same piston diameter) but has rectangular friction pads for more surface area.

The CM400 is also a floating-caliper design, so the caliper body is rigidly mounted to the dual fork lugs on the fork lowers and internals float left and right with pad wear.

The CM400 fork tubes are about 2" longer than the CB400F forks, so to keep the ride height, they need to be raised about 1.5" in the triple clamps. I found that after installation, the bike's weight brings it closer to 1.5" difference.

It looks perfect to me after installation, and in fact if you are a cafe dude, it allows a placement to mount 33mm clip-ons!

I'm keeping the amazing CB400F low tubular bars... the best ever stock bars from Honda!

I started with a drilled and surface-ground OEM CB400F rotor, machined by TrueDisk LLC

tokarz48117@hotmail.com

This guy is fantastic, and has been used by many others here on this forum.

Soon, I realized the OEM 400F rotor did not work with my new forks and caliper position, due to pad and rotor contact diameters.

So, I transferred the newly drilled and surfaced rotor to my 2nd CB400F (yellow) with the stock front front-mounted circular-pad caliper...perfect!

It works SO MUCH better than the old, warped, glazed stock rotor.

Anyway, I ended up using the CM400 forks and a fixed caliper with a floating center section, rectangular pads and a Chinese CM400 rotor I got on AliExpress.

The CM400 rotor is thinner than the CB400F rotor, so it works as intended with the CM400 caliper.

I had to make an aluminum adapter plate on my lathe that had a centering relief for the center hole, and an offset outward that would place the flatter CM400 rotor in the center of the pad grip section.

I did that on my trusty Harbor Freight mini lathe, and it worked out well.

I drilled the 4 holes for the CB400F hub, and drilled the 6-hole rotor for the other two holes.

Not as squeaky-clean as it sounds, as I had to oblong two of the CM400 rotor holes (larger BC)

It all worked out just fine, and it works just great!

I replaced my drippy OEM circular-lid master cylinder (kept blowing DOT 3 onto my fuel-tank paint!)

I got a CM400 (rectangular lid) master cylinder and installed a new custom Venhill single-line brake line direct to the caliper.

I wired the original brake light sensor wires directly to the new master cylinder switch.

Here are a few photos that show the progress:

Here's one with the CB400 drilled rotor and the CM400 forks and rear caliper:



Here's another one with the CM400 drilled rotor and my adapter plate:



And some more:







The braking power is immensely better on both of the bikes... due to drilled rotors I suspect

BLIGHT

 

[blight]

Hey guys,

Doesn't seem to be much interest here in this brake upgrade.. seems odd because the CB400F brake is so rotten!

I'm still posting on the project progress in case there is someone else that wants to try it someday.

Anyway, with the 33mm CM400 forks installed, it offers some more options for back-mount calipers with 65mm hole centers on the mounting bracket.

I've been riding around for a few hundred miles on the CM400 single-piston rear-mount floating caliper, and it's a lot better than the stock setup.

The single piston & seal is even the same size as the CB400F pivoting caliper. The main difference is the rectangular pads on the CM vs. round pads on the CB, and floating vs. pivoting.

So, looking thru my parts bins, I pulled out a twin-piston caliper used on several different Honda street bikes... both CB's and VF's (an '81 CB900F in this case from ebay)

This caliper style has 'banana-shaped' curved pads and twin (smaller) pistons.

The caliper floats in and out with pad wear, and there are now 2 pistons contacting the pads... it bolts right up to the CM400 slider mounts, with a washer on each bolt to adjust for caliper/disc clearance. Looks pretty stock if you didn't know better. Even has 'HONDA' cast into the caliper.



WOW... what a difference! Now it's down to a single-finger pull to stop in most situations. I only put a couple of miles on the new EBC sintered pads, but they were way better right out of the box.

I also have a new left-side Brembo 4-piston caliper that I still want to try, and I think it has a similar 65mm mounting... we'll see if it will clear the spokes on the inside! It's pretty long, so may foul the lower fender brace. The brace clearance with this twin-piston is about a business-card width!

Also have a new 260mm floating universal rotor on order from China (Ali-Express) and it should be here in a few days to play around with. It's flat (no offset) with 5 holes, so will need to machine a thicker spacer/hub adapter.

Signing off for now... I'll just keep riding and see if it improves with the new pads bedding-in.

I put ~60 lovely miles on it today... about 72 deg F here on Nov. 9th.... beautiful sunny weather!

BLIGHT

[scrambler]

Hey there, that Ascot looks awesome! It must be really fun to ride. I had a VT500E a few years ago, I loved it. How did you couple the rear hub with the shaft drive?

[Don R]

 I put 1985 V65 32mm twin piston brakes on my 78 gl1000 on 1985 1100 twin Sabre brackets. (they have 30mm calipers)  I made small drop brackets for the lower fender brace to clear the caliper bottoms. Some guys just bend the brace but I prefer to leave it bolt on and return to stock capable. These also interfere with spoke wheels, work fine on comstars. 
 There are lots of swapping possibilities with the Honda brakes. Many brackets have the same centers and offsets.

[blight]

Hey there, that Ascot looks awesome! It must be really fun to ride. I had a VT500E a few years ago, I loved it. How did you couple the rear hub with the shaft drive?

Thanks, the Ascot had ugly cast wheels, so....it was a lot of work, but here's how I did it:

Bought a used Comstar shaft-drive rear wheel from a UK ebay seller. (I think it was from a euro CX500)

Stripped off all the Comstar bolt-on & riveted stuff, including the alloy rim, leaving the bare hub and drum brake cavity.

Machined up two flat 'spoke-flanges' (look closely at the pics) from 6061-T6 plate, and drilled for spokes, counter-sinking for the shanks.

Bolted completed spoke flanges to the Comstar hub, grade 8 fasteners.

Ordered custom HD S.S. spokes and nipples from Buchanan's

Ordered new flanged alloy 18" rear rim, Akront-style

Laced up spokes to new rim to new drilled hub, trued radially and axially,  and balanced it.

Mounted up new 18" Bridgestone Battlax tire and tube, rebalanced assy.

Mounted up the the rear hub with stock rear axle and brake drum to the bike.

Easy, right?

No... I just make it look that way!

BLIGHT