Twindisk front end with 18" wheel?

So..... Am really liking the idea of upgrading the front end of my cb360 to twin disks.

I want period 1970's disks not modern stuff or usd forks etc.

Im thinking of using a '74 cb450 lower triple as i believe this has the same stem length as the 360? ( probably a billet upper and taper bearings)

Then it's a pair of cb550 35mm forks with disk mounts on both, cb550 hub and disks.
(I believe 750 forks would also do but are longer?)

My question is : can i retain the cb360 rim, lacing it to the 550 hub or do i have to go for the full 550 front end with 19" wheel?

Thanks for helpful advice from those who've done this before as i havent!

Steve

I do not have specific parts advice - sorry - but do advise against adding the extra disc for looks only. The single OEM disc on your 360 may not be the most killer brake around, but should be plenty powerful unless you have some difficulty with strength in your right hand. The extra disc and caliper add very considerable extra weight and will be an over all performance downgrade - trading handling and suspension performance for increased braking power. If you don't NEED more brakes, it isn't a good trade.

If the rim and hub have the same amount of holes there's no reason you can't buy the proper length spokes to accommodate the swap. try Buchannons for spokes.

So.... I bought a cheap set of cb550 forks on ebay, tatty but solid.

The cb360 wheel is 36 spoke and the 550 is 40 spoke, so im now thinking of using the whole 360 wheel.

Ive mocked up the cb360 wheel in the 550 forks, and swapped the disk over to check it will line up.

All looks good, calipers line up ok, will need a couple of spacers to accomodate the wider fork gap.

The cb360 speedo drive is too thick with a second disk in place.

I think i read that a cb550 speedo drive is thinner, and fixes this issue but cant find that thread now.

Does anyone know the thickness of a cb550 speedo drive, or could measure one for me ?
Otherwise ill buy one to try.....

Thanks !

360 wheel will fit fine with 550 forks, just use 550 axle and get some new spacers made to center wheel in forks.
You also need longer bolts to fit dual disc. The rotors are smaller diameter on 360/400f (et.al.) so you'll need to either modify pivot arms or fit larger diameter rotors, maybe with adapters? (take a look at Neevo's CB400f with 18" wheel, CBR600 rotors, GSXR forks)
I wouldn't worry about 'too much brake' that isn't possible you just have to learn to use front brake properly. You will need different master cylinder. You need CB500 drive unit or modify CB360 one. You need a 'flat' drive piece where it fits onto hub. There are pictures of it and modified stock ones on SOHC4.net as dual disc is very common conversion for CB550/750 (principle is exactly the same even if dimensions are not)

Thanks for the input crazypj

Im working this through in the garage at the moment.

Presently it looks like i can (just about!) squeeze the standard 360 speedo drive in.

Ive made custom spacers, cut down from originals, and it all seems to just fit.

Awaiting longer bolts for a trial build.

Then i plan to modify the caliper arms to drop the calipers onto the 360 disks, only seem to need to drop them 3-5mm.

Im on a 14mm master cylinder at the moment, non original.
With one caliper there is very little lever travel, so im thinking it will probably still be ok with 2 calipers.

Once its mocked up and given a little test i'll strip it all off and paint.

Must post photos!

Steve

You can't fit the chrome hub cover and drive with dual disc, I don't know how to describe it easily. If I can find the pieces I have I'll get some pictures. I know there was someone on SOHC4.net making a new piece to fit with dual disc but don't remember if it was only for the 500/550750 (which have 6 bolt rotors)

Progress!

The bike is built back up with Renthal flat bars and the cb550 front end with twin disks and the cb360 18" front wheel.

All is good!

The 18" wheel works ok, i made custom spacers to centre it and the speedo drive just fits.
I modified the calliper swing arms to lower the callipers onto the 360 disks.
Shimming the calliper arms so the calliper is parallel with the disk is critical, both vertically and horizontally, otherwide the brakes jam when bolted up.

The Renthal flat bars are lovely, look good and so much more comfortable that the clipons. I liked the look of the clipons but couldnt live with the discomfort.

Ive added a micron fork brace too.

Only a short test ride but the bike feels more stable than before, particularly in sweeping turns.

Brakes are significantly improved and still to bed in.

Overall im very pleased with the look and performance of the conversion.

Both the Renthal flat bars and the brakes/suspension have worked out well.

Close up!

You're missing the screw and spring that centers the caliper(s). I'm not sure I see how they'd work correctly without it....it seems the piston would just push the caliper off the disc.

scott s said:

You're missing the screw and spring that centers the caliper(s). I'm not sure I see how they'd work correctly without it....it seems the piston would just push the caliper off the disc.

Click to expand...

It'll work, but the fixed caliper will drag. The spring pulls it off the disc, while the other caliper retracts.

All that really happens is caliper rattles.
The main reason for keeping it in place is to prevent brake backing off too far which could be fatal on the street
The spring causes some rubbing when the pads wear unless you adjust every 500 miles or so

I do plan to make some 'bent' caliper adjusting bolts

the holes do not line up due to having to modify the swing arms to lower the callipers onto the 360 disks.

Brakes are working well, i have ebc semi sintered pads in and am pleased with them.

Handling is good, very stable in turns but maybe a tiny bit twitchy at walking pace?

Steve

If it's deep enough, you could just bolt a bracket onto stock location and use stock screw.
It doesn't need top supply a ton of torque, just enough so caliper can't back off if it gets bumped or something. Even then, as long as your not waiting until last second, you can 'pump' the brakes a couple of times to get back where you were