Author Topic: Twin Disc Conversion - CB400F (Read 4837 times)

Senna27 · « **on:** January 12, 2010, 12:06:14 pm »

What is involved in doing a twin disc conversion on a '75 CB400F. I've searched for about half an hour but didn't find much info. If there's something already on the topic that applies to my bike, please post a link.

Thanks...

domer · « **Reply #1 on:** January 12, 2010, 12:17:22 pm »

shortly... dual disc lower forks (which i have if you need) another caliper and rotor. master cylinder and brake lines for dual disk. im not 100% on this but , you might be able to drill your current hub to accomadate the extra rotor... a lot of people seem to use harley hubs laced to the cb rim... oh and the speedo drive, not sure about that one... anyone else?

turboguzzi · « **Reply #2 on:** January 12, 2010, 12:18:31 pm »

check the faq, tons of posts on the subject

paulages · « **Reply #3 on:** January 12, 2010, 12:25:46 pm »

Unless I'm mistaken, you'll need 550 or 750 forks, as the 400 doesn't have brake mounts on the right leg.

Senna27 · « **Reply #4 on:** January 12, 2010, 01:32:56 pm »

Quote from: turboguzzi on January 12, 2010, 12:18:31 pm

check the faq, tons of posts on the subject

Really? I went through the FAQ and search but I didn't find anything specific to the CB400F. Lots on 550/750's. Am I missing something?

domer · « **Reply #5 on:** January 12, 2010, 02:34:30 pm »

i should have stated the fork lowers i have are from a 550.... 35mm..

turboguzzi · « **Reply #6 on:** January 12, 2010, 02:44:03 pm »

Quote from: Senna27 on January 12, 2010, 01:32:56 pm

Quote from: turboguzzi on January 12, 2010, 12:18:31 pm
check the faq, tons of posts on the subject
Really? I went through the FAQ and search but I didn't find anything specific to the CB400F. Lots on 550/750's. Am I missing something?

yes

Quote from: paulages on January 12, 2010, 12:25:46 pm

Unless I'm mistaken, you'll need 550 or 750 forks, as the 400 doesn't have brake mounts on the right leg.

TomC · « **Reply #7 on:** January 12, 2010, 04:33:37 pm »

Hi Senna27
Find a second left slider and put it on the right. Which would end up with one caliper to the back and one to the front. The usual speedometer drive problems. Classic Bike or maybe Real Classic had an article on Trident with dual disks with one caliper to the front and one caliper to the rear. Or weld mounts to the right slider.
Or fix some other fork. 550 forks with 450 twin cam triple trees or ?.
But why?
TomC in Ohio

Quote from: Senna27 on January 12, 2010, 12:06:14 pm

What is involved in doing a twin disc conversion on a '75 CB400F. I've searched for about half an hour but didn't find much info. If there's something already on the topic that applies to my bike, please post a link.

Thanks...

bryanj · « **Reply #8 on:** January 12, 2010, 08:06:38 pm »

The 400 is awkward due to a lot of things being different from all other fours

Fork tube diameter
Disc diameter and number of holding bolts
rim size
Etc, Etc

Only way using 400 parts is another LH slider fitted to RH side
Modify the mudguard mount to fit
another 400 caliper with mount so one is in front the other behind
Use a second 400 disc with longer bolts--modify speedo drive as per 500/750
GL1000 master cylinder

domer · « **Reply #9 on:** January 12, 2010, 09:05:36 pm »

ouch... i apologize, that poor 400 has 33mm forks. so ya, with out a front end swap... which might be a good idea anyway...especially if your pounding that sucker hard enough to need dual disk...cosmetically, the front to back seems to be the way to go...

Rich361 · « **Reply #10 on:** January 13, 2010, 04:08:37 pm »

Hi, Have a look at this page... http://cafe400f.cloud.prohosting.com/html/CB400f_Dual_Disk_Project.htm

Senna27 · « **Reply #11 on:** January 15, 2010, 09:09:47 am »

Quote from: Rich361 on January 13, 2010, 04:08:37 pm

Hi, Have a look at this page... http://cafe400f.cloud.prohosting.com/html/CB400f_Dual_Disk_Project.htm

That's what I was looking for... Thank you!

fasturd · « **Reply #12 on:** March 12, 2010, 07:13:00 pm »

Yoshima just welded another mount to the 400 forks and used a second caliper set. Worked for him... Of course you need to weld rather than just bolt on...

jakec · « **Reply #13 on:** July 17, 2018, 12:45:15 pm »

Unfortunately the link above is no longer working.

In researching this topic I have found some 400's that have made the swap but I have not yet been able to find a definitive build thread with a 400 that swaps to dual discs on a 550 or 750 front end. DCC has their "the 400" build which in an article is purported to have a combination "400, 450, and 750 front end." My guess was that the forks and/or wheel were 550/750, with a 450 triple. I actually emailed DCC looking for more info on that build.

I had thought about getting a second right side fork lower and have the calipers reversed but I'm not sure how nice that would look. If any one has a photo of that set up please share. I like the idea as it would involve the least headache.

Until reading this thread I did not realize that the 550 fork tubes were a larger diameter than the 400. I seem to remember reading threads where people used 550 front ends and talked about dropping the forks about 3/4" in the tree. Would they have needed to swap the tree as well, as suggested in this thread? And why in this thread does someone suggest a 450 tree over a 550? If you swap the tree with anything other than a 550 super sport tree, would the 400 headlight/blinker array and dash still line up once mounted?

If you swap the forks and tree for a 550, i'm assuming you need the wheel and fender as well, at which point you're looking at a whole 550 front end.

There is a good discussion here, but no real conclusion:

http://forums.sohc4.net/index.php/topic,103463.25.html

Tim2005 · « **Reply #14 on:** July 17, 2018, 03:07:54 pm »

Hi Jake, luckily that article is archived here

https://web.archive.org/web/20091226042822/http://cafe400f.cloud.prohosting.com/html/CB400f_Dual_Disk_Project.htm

Also, there is another option, Honda RSC did make a right lower leg with the caliper mounting, however they are very rare and would be hard to find and expensive.

jakec · « **Reply #15 on:** July 17, 2018, 04:37:31 pm »

That was a good read, thank you. Unfortunately I looks like a lot of modification is required when you go with the 450 triple and the 550 front end. My goal would be to keep the bike as close to stock as possible, and that most likely means going with A. the inverted second caliper, B. Maybe finding an example of this rare right side fork lower, or C. keeping it as-is, since it's not totally necessary, more just for fun. I would be very interested to see an example of the 400f with the second caliper inverted!

scottly · « **Reply #16 on:** July 17, 2018, 10:07:07 pm »

Quote from: jakec on July 17, 2018, 04:37:31 pm

My goal would be to keep the bike as close to stock as possible

It may be possible to re-drill a larger 750 rotor carrier to the 400 4 bolt pattern. The 750 F0/F1 K7/K8 calipers are very similar in appearance to the 400/550 calipers, but are larger bore, and use the same mounts. The larger rotor with the larger caliper will improve the braking significantly, while appearing stock to the untrained eye.

RAF122S · « **Reply #17 on:** July 17, 2018, 11:17:30 pm »

Godfrey's thinned disc are removed from the carrier. Are the disc stainless steel portion ID and OD compatible in size and rivet locations? If so, easy solution if offsets are in range... Put 400 rotor center on 550 or 750 disc... The thinned discs are a good idea if going twin discs as it lowers the weight gain without compromising anything. It even makes fitting new pads easier...
David

jakec · « **Reply #18 on:** July 18, 2018, 09:50:07 am »

Quote from: scottly on July 17, 2018, 10:07:07 pm

Quote from: jakec on July 17, 2018, 04:37:31 pm
My goal would be to keep the bike as close to stock as possible
It may be possible to re-drill a larger 750 rotor carrier to the 400 4 bolt pattern. The 750 F0/F1 K7/K8 calipers are very similar in appearance to the 400/550 calipers, but are larger bore, and use the same mounts. The larger rotor with the larger caliper will improve the braking significantly, while appearing stock to the untrained eye.

Are you saying mount up a (single) 750 rotor and caliper to the 400 fork lower? That would be cool! Not a bad idea.

Unfortunately I really did like th eidea of a 550 front end swap for the increased rigidity in the forks. However I'm not willing to compromise the look of the bike. At the end of the day I'm doing "spirited" riding at best.

scottly · « **Reply #19 on:** July 18, 2018, 07:22:07 pm »

I took some quick measurements, and it's not feasible to swap a 750 brake onto a 400.

David, the ID/OD of the steel rotor parts, and the rivet location and number are different...

Bodi · « **Reply #20 on:** July 19, 2018, 12:51:10 am »

About the only way that works and looks good is to use the 450 triples and legs that fit it with dual disks... but it's a big job. The larger diameter tubes should improve handling.
I don't think the 450 legs have disk mounts on both sides, but as I understand it they are better forks than most - the damper is different?
I think the key is that this preserves the steering geometry, other triples have different offsets.
I've seen a 400 with the reverse brake on one side, it looks pretty odd - sorry no picture. I have a set of forks and could try that but I didn't like the appearance. Welding the mounts on... risky for strength (do not want the caliper coming free in a panic stop!) and for distortion of the tube as the damper fit is pretty tight.
And of course the speedo drive becomes a PITA to mount with any dual disk setup.

jakec · « **Reply #21 on:** July 20, 2018, 11:42:29 am »

If you can't find a photo of the dual disc set up, make your own... right?

754 · « **Reply #22 on:** July 20, 2018, 12:27:27 pm »

Not sure if EBC makes anything, that might help.
I THINK removing stock disc and riveting on cast iron rotor could help.
Switching to 35 mm trees opens many possibilities, like running F model discs, much lighter.

I bet TTR 400 has some good ideas re, improving 400 4 brakes.

jakec · « **Reply #23 on:** October 09, 2018, 01:10:40 pm »

I found someone who is willing to sell me the complete brake setup including the fork lower. Another question that has popped into my head is the axle. Does anyone know off the top of their head if the two ends (intregral end and end with nut) are the same diameter? From eyeing it I would say yes. But I don't know. If they are not the same then I would not be able to use two of the same fork lowers.

Bodi · « **Reply #24 on:** October 09, 2018, 08:00:08 pm »

The caps that clamp the axle are interchangeable so the nut and extended axle head are the same size, if that's what you're asking.

jakec · « **Reply #25 on:** October 10, 2018, 09:07:07 am »

That is what I was wondering, thank you. I looked at the fender last night and it seemed like it was slightly offcenter. Obviously the mounts are a little different but I'm wondering if the fender is really supposed to be offcenter when the wheel is centered? Maybe the one I was looking at was just slightly bent.

Don R · « **Reply #26 on:** October 10, 2018, 06:35:39 pm »

I'm too anal for one in front one in back. There were a couple pics in the small block thread. cb360 forks are the same as cb400F too. Still only left side brake.

jakec · « **Reply #27 on:** October 15, 2018, 09:34:55 am »

Quote from: Don R on October 10, 2018, 06:35:39 pm

I'm too anal for one in front one in back. There were a couple pics in the small block thread. cb360 forks are the same as cb400F too. Still only left side brake.

In the little F'ers thread? I just skimmed it but the only one I saw was Kevin's and it has the aftermarket lowers that put the calipers both in the front.

Don R · « **Reply #28 on:** October 15, 2018, 10:59:35 am »

Maybe that's the one I remember. Sorry. I dug out my 400 stuff, I have a pair of standard forks but with air caps on them.

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Author Topic: Twin Disc Conversion - CB400F (Read 4837 times)