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.


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

[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.

 The best part of that brake swap is that it looks right, could be stock original.

[scottly]

I figured this thread should be saved here, after separating the wheat from the chaff.
BTW, there is no spoke interference problem with the two piston calipers.