Author Topic: CB750 Dual Disc Conversion - Speedo Drive Mod and Bolts (Read 42539 times)

spiritof67 · « **on:** June 20, 2009, 04:57:46 PM »

Can anyone remind me what it was we have to do to the speedo drive on the front hub to allow use of dual discs? And what is a source (and the sizes) of the bolts used for twin discs? My setup was Checkered Flag Customs (mag caliper mounting and all)? Wait - one more: is there a source for new discs for a CB750 KO-K5 that don't cost $480 like the OEM replacements do?

Spirit

robe0531 · « **Reply #1 on:** June 20, 2009, 05:01:52 PM »

take a look at this link it may help has alot of info in it
http://www.salocal.com/sohc/tech/dual_disks/dual_disks.htm

bwaller · « **Reply #2 on:** June 20, 2009, 05:12:46 PM »

Checkered Flag Customs, were they not partnered in some way with Yoshimura when Pops started operations here?

You'll need to alter the drive plate to match the cut-outs in the front hub. For bolts I just used good longer non metric.

You can get used discs ground for short money and end up "like new"

Ignore that disc pic, just meant to show the drive plate ears aligning with the hub.

spiritof67 · « **Reply #3 on:** June 20, 2009, 06:51:44 PM »

re: CFC, if I recall the story (correction needed?) the guy who became CFC tried to take over Yoshimura but didn't.

Is it really true that a Cb550 speedo drive removes the need to reduce a CB750 one and can be used with no mods?

robe0531 · « **Reply #4 on:** June 20, 2009, 07:13:04 PM »

i really do not know i have yet to do the conversion

bwaller · « **Reply #5 on:** June 20, 2009, 08:24:07 PM »

Quote from: spiritof67 on June 20, 2009, 06:51:44 PM

re: CFC, if I recall the story (correction needed?) the guy who became CFC tried to take over Yoshimura but didn't.

Is it really true that a Cb550 speedo drive removes the need to reduce a CB750 one and can be used with no mods?

[/b]

Nope.

ev0lve · « **Reply #6 on:** June 20, 2009, 08:35:45 PM »

Quote from: spiritof67 on June 20, 2009, 06:51:44 PM

re: CFC, if I recall the story (correction needed?) the guy who became CFC tried to take over Yoshimura but didn't.

Is it really true that a Cb550 speedo drive removes the need to reduce a CB750 one and can be used with no mods?

The drive plate is the same for both models. Wish someone would correct that in the FAQ. As I understand it the K0 model is the one that can be used with no mods but that may be spurious as I don't have a K0 to look at

Should look like this installed

You can read my misadventures with the SaLocal FAQ here if it's helpful
http://forums.sohc4.net/index.php?topic=38242.msg493516#msg493516
http://forums.sohc4.net/index.php?topic=38242.msg514899#msg514899

SaLocal's list of parts required is right on minus the CB550 drive plate

1x caliper arm
1x caliper
1x disc
6x8mmx110mm bolt (for disc)
1xlower brake line (that makes two all up)
1x steel brake line to caliper (which again makes two all up)
1xdouble banjo fitting (for the two lower brake lines)
1x bigger master cylinder (some say GL goldwing mastercylinder are ok.. I used one off a modern dual disc bike)
1xcb500/550 speedo drive plate (no modification) NO NO NO NO NO
2x6mmx30mm bolts and washers
1x8mmx35mm bolt and washer

cben750f0 · « **Reply #7 on:** June 21, 2009, 04:56:32 AM »

thats funny i have managed to change that everywhere this write up has turned up, except here...

yeah it was a K0 drive plate i lucked out with when doin the write up, you need to mod a standard one to drive, though there are a couple of ppl on here who have modded there discs to suit.

hope that helps

peace

Steve F · « **Reply #8 on:** June 21, 2009, 07:01:13 PM »

Here's what I had to do to get mine to work. It involved milling pockets in the rotor to fit the drive ears on the speedo drive. The speedo drive was modified, ground down on the diameter to fit within the rotor bore. On the fork, one of the cast bosses for the spring was cast off center and the bolt's locking nut had to be fitted to the inboard side because the bolt was too short to reach through because of the off-center casting. The caliper mount for the right side had to be shimmed out about 2mm to get the caliper to center over the rotor, as shown in one of the pics. The longer bolts were special ordered long stainless bolts that had to be shortened a bit, and the heads turned slightly to clear the speedo drive by about 1mm

. Really close, but they clear.

Steve F

cben750f0 · « **Reply #9 on:** June 21, 2009, 07:21:31 PM »

had to do the same thing steve, with the adjuster spring and screw.

great pics.

peace

SKTP · « **Reply #10 on:** June 21, 2009, 08:30:33 PM »

Excellent info guys...I did buy a 550 speedo but it looks like that will be going back on ebay...that milling method looks pretty slick. I do not have the equipment to do that...any guesses on what a fair price for a machine shop to do that would be?

mystic_1 · « **Reply #11 on:** June 21, 2009, 08:50:22 PM »

If your front hubs has the flats for the early speedo drive, you can modify the later drive plate to work.

http://forums.sohc4.net/index.php?topic=37258.msg387590#msg387590

mystic_1

MCRider · « **Reply #12 on:** June 21, 2009, 08:58:06 PM »

Quote from: mystic_1 on June 21, 2009, 08:50:22 PM

If your front hubs has the flats for the early speedo drive, you can modify the later drive plate to work.

http://forums.sohc4.net/index.php?topic=37258.msg387590#msg387590

mystic_1

I believe that picture is one of mine from some time back. The speedo drive can be altered on the cheap with a bench grinder and a pair of vice grips (the one on the right) It worked for over 15 years and 50000 miles.

The earlier picture is one of mine also, the drive has been radiused down on a mill and two tabs welded into place. The machinist charged me $35 i think. Looks nicer than my grounded down one.

I would think modifying the drive plate to be easier than modifying the disc, but I'm no machinist.

SKTP · « **Reply #13 on:** June 22, 2009, 09:57:30 PM »

I have almost assembled all of the parts in need to do the conversion. Before I proceed, I have a question to all you converts; Was it worth it?

I suspect the answer is yes, but if it isn't now (before I send my rotors out to be cross-drilled and order my master cylinder and Stainless brakelines) is as good a time as any...if I end up with 2 screeching brakes instead of the one I already have...I am going to be bummed...thanks for your input and all of these awesome reference photos and tutorials...

also, anymore info on what bolts you used would be awesome....thanks

ev0lve · « **Reply #14 on:** June 22, 2009, 10:09:28 PM »

Mine squeal. A lot. But I failed to put some brake grease on the pistons. Right now, when it rains, the squeal is gone. Dries up and it's back so I'm pretty convinced the grease will fix it.

There was some talk in some thread somewhere of a nylon spacer to dampen the vibration that causes the squeal as well. Anyone done that with success?

Overall, I'd do it again for sure. I'd just be smrtr about it

Here's the notes I made to myself concerning the adjusters if it's helpful

I used exactly the list in the FAQ otherwise.

Steve F · « **Reply #15 on:** June 23, 2009, 04:35:26 AM »

Once I started using the brake pads from Parts n more, the squealing stopped. I like having the duals and don't regret the conversion at all. Before you go out and buy your brake lines, I would suggest that you mock everything up on the bike to be sure you don't order brake lines that are too short (or too long for that matter). I had everything in place, the master cyl, and the calipers, and used some 12 ga. wire to simulate where I wanted to run the lines, then measured each wire to determine the lengths that I needed.

SKTP · « **Reply #16 on:** June 23, 2009, 05:35:54 PM »

Do you guys run a short length of "hardline" from the caliper to the brake line on the new/speedo side? If so, I'd love to see pictures...thanks

SKTP · « **Reply #17 on:** June 25, 2009, 01:32:53 PM »

Sorry, bumping this back from page 7...

MCRider · « **Reply #18 on:** June 25, 2009, 01:40:07 PM »

Quote from: SKTP on June 25, 2009, 01:32:53 PM

Sorry, bumping this back from page 7...

Doubt that many do this. Mostly, run the SS braid straight into the caliper with appropriate fitting.

Steve F · « **Reply #19 on:** June 27, 2009, 07:03:09 PM »

Quote from: MCRider on June 25, 2009, 01:40:07 PM

Quote from: SKTP on June 25, 2009, 01:32:53 PM
Sorry, bumping this back from page 7...
Doubt that many do this. Mostly, run the SS braid straight into the caliper with appropriate fitting.

I agree.

SKTP · « **Reply #20 on:** July 19, 2009, 03:57:27 PM »

Yep...dragging this one up again. I will be modifying my speedo-drive-plate this week

Question; Should the modified drive plate be exactly flush with the outer surface of the disk?

I believe so...want to double check before I tear in...thanks

ALso I am running lester mags and they do nto seem to have the catch notches on the hub...I'm thinking this idea...From this thread might be the best way to go? http://forums.sohc4.net/index.php?topic=49178.0 (see below)

MCRider · « **Reply #21 on:** July 19, 2009, 04:46:02 PM »

Your pictures throw me off a little, but if memory serves, the speedo drive plate (modified) must lay flat against the hub, with its two little turned down tabs engaging the flats of the hub.

My experience is with a CB750K2.

Where it ends up relative to the disc is not material, but I think it will be lower than flush. The gearbox will fit down in the disc a ways.

But I've been wrong before.

Don R · « **Reply #22 on:** July 19, 2009, 05:07:15 PM »

I might be the lucky one here. Mine is a K0 with lesters and there are already washers stacked between the speedo drive and the hub. I am hoping to remove the washers and insert a rotor where they are. I have to assume something is turning the speedo drive now.

Edit, it's 11 years later I never double disc'ed this bike. Still have it and it was bike of the month once. I did rework the speedo drive and pinned it to the hub. I since doubled a 76F and loved it with the stock M/C.

bikebitzofvt · « **Reply #23 on:** July 19, 2009, 05:23:04 PM »

I really like the idea of milling the back side of the rotor boss to accept the drive. That area is plenty thick enough! Now if I could find a milling machine...

fishhead · « **Reply #24 on:** July 20, 2009, 05:26:05 AM »

What you could do to get around not having the "flats" in your hub is to modify the stock single disc speedo drive is to make it drive like the GL 1000 does (tabs driven by the disc bolts).

The pic shows
Left to right
1) stock single disc speedo drive. The 2 chrome covers have the "bump outs" for engaging the speedo drive, the top chrome cover is cut down for clearance for the speedo on a dual disc set up.
2) Sandcast speedo drives and chrome covers. No bump outs on the chrome covers for the drive tabs. This style is typically used on the Dual disc conversions.
3) 75-77 GL 1000 speedo drives (too wide to fit on the CB series). The speedo drive has "tangs" instead of the bent down corners of the Sandcast drive. The chrome cover has "bump outs" for the speedo drive tangs. The GL 1000 speedo drive wont work on the CB (too wide).
4) Modified stock speedo drives for dual discs (bent down edges for the flats in the hub)

If you take the stock single disc drive, cut it down and then bend "tangs" out to drive like the GL 1000 does, it would work fine on the uncut hub. The chrome cover off a GL 1000 would fit (or a cut down chrome cover for a single disc) would cover up the "handy work" but it is not really needed as it would be driven by the heads of the bolts(bolts go in from the speedo side for speedo clearance).

I have machined out the whole inner diameter of the brake disc carrier to allow the stock uncut CB speedo drive to be used on a dual disc(the uncut speedo drive is mounted on the hub and the disc fits over it). It would be easier to file grooves in the disc carrier and modify the speedo drive as shown above though.

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Author Topic: CB750 Dual Disc Conversion - Speedo Drive Mod and Bolts (Read 42539 times)