Author Topic: 1978 cb750k dual DISK Convert Question (Read 2240 times)

Ericcb750 · « **on:** July 10, 2014, 09:52:34 AM »

Hey guys, I'm looking to do the dual disk conversion to my 78 750k. I just have one quick question as I'm going to have to pick up parts for the right side (caliper, arm, rotor, etc.) Is there an actual specific caliper/arm for the right side of the forks?? Or can you just turn it around to fit the right side rather than the left? I just wondering if I have to hunt down a Right side only Set of brake parts or if I can just get a normal left side caliper/arm, etc and turn it around? I've never done this before so i'm a rookie. Any help/advice on buying the parts would be great. Also I've read some threads about the conversion and Modifying the speedo drive? Can this be done to the stock 750 one or will the 550 work as it is? Or do both need modifying??

Thank you all for your help, I really appreciate it. Take it easy.

theslayedsaint · « **Reply #1 on:** July 10, 2014, 10:02:28 AM »

Hey i'm really new at this too! so take this with a grain of salt. But I was told at a very well known shop in town that the only thing you need is a new brake set up and master cylinder and no i don't believe they make different sides. Honda at the time made this bike capable of dual disk for racing. the part i was told would be hard to find was the bolts you need to attach the caliper on. I'm also looking to do this to my K4 so if i come across any more info i'll be sure to let you know. good luck!

flybox1 · « **Reply #2 on:** July 10, 2014, 10:06:45 AM »

for the caliper arm mount, yes, just flip it around for it to work.
you'll need a second rotor, 110 mm rotor bolts, with short heads to clear the (modified by you) speedo drive plate, and a bunch of fasterners....not to mention a new brake line and fittings at the calipers. A 14mm master cyl. is recommended.

see these...the first is from my build thread which discusses fitting issues and suggestions.
http://forums.sohc4.net/index.php?topic=105018.msg1341362#msg1341362

this one has part lists for all the bolts you'll need
http://forums.sohc4.net/index.php?topic=53532.0

750K · « **Reply #3 on:** July 10, 2014, 10:09:42 AM »

Someone that's actually done it will chime in I'm sure but as far as I've read the caliper arm just flips over, iirc the hard line in and the bleeder screw get reversed on the new caliper. You'll need longer bolts for the rotor and 750 speedo needs to be modified to fit. Some say upgrade the master cylinder others say stock is fine.

I've had this one on my to do list and have a parts bike with most of the items sitting in the garage, just need the time to tear it all apart and do it.

lucky · « **Reply #4 on:** July 10, 2014, 10:38:57 AM »

Quote from: theslayedsaint on July 10, 2014, 10:02:28 AM

Hey i'm really new at this too! so take this with a grain of salt. But I was told at a very well known shop in town that the only thing you need is a new brake set up and master cylinder and no i don't believe they make different sides. Honda at the time made this bike capable of dual disk for racing. the part i was told would be hard to find was the bolts you need to attach the caliper on. I'm also looking to do this to my K4 so if i come across any more info i'll be sure to let you know. good luck!

The 77-78 brakes are larger diameter.
Will not mix with the earlier parts.

Ericcb750 · « **Reply #5 on:** July 10, 2014, 11:42:45 AM »

HEy guys, thank you all for the help/tips. So if I get a cb 750 rotor and a regular caplier/arm I should be good... Sounds like a plan. I will look into getting a different Master cyl and hoses , stuff like that. I have the stock 77/78 brake setup on the left side.

Lucky, so if I get a brake setup say from a k6 (rotor and caliper) , Is it different size than the 77/78 ?? Like will it look weird? Anyone done this for a 77/78 before? Were you able to use another year's brake parts?

Wobbly · « **Reply #6 on:** July 10, 2014, 12:05:24 PM »

There are numerous threads here that already discuss, in great detail with lots of picture, how this set up was done on your specific model.

MiGhost · « **Reply #7 on:** July 10, 2014, 01:08:17 PM »

Quote from: lucky on July 10, 2014, 10:38:57 AM

The 77-78 brakes are larger diameter.
Will not mix with the earlier parts.

Maybe a recheck of the part # is in order.
45120-392-000 DISK, FR. BRAKE
Used on the following.
71-78 CB750K (K1-K8)
75-76 CB750F
76-77 CB750A

flybox1 · « **Reply #8 on:** July 10, 2014, 01:16:47 PM »

Quote from: MiGhost on July 10, 2014, 01:08:17 PM

Quote from: lucky on July 10, 2014, 10:38:57 AM

The 77-78 brakes are larger diameter.
Will not mix with the earlier parts.

Maybe a recheck of the part # is in order.
45120-392-000 DISK, FR. BRAKE
Used on the following.
71-78 CB750K (K1-K8)
75-76 CB750F
76-77 CB750A

exactly

the only real installation difference to be aware of is the difference betwee early and late calipers(piston side housing offset) and caliper arms (mount area width @ 2 bolts) cant mix-n-match parts here. the bleed hole/brake line hole locations differ between early and late, too.

Eydugstr · « **Reply #9 on:** July 10, 2014, 01:29:37 PM »

Quote from: Ericcb750 on July 10, 2014, 11:42:45 AM

HEy guys, thank you all for the help/tips. So if I get a cb 750 rotor and a regular caplier/arm I should be good... Sounds like a plan. I will look into getting a different Master cyl and hoses , stuff like that. I have the stock 77/78 brake setup on the left side.

Lucky, so if I get a brake setup say from a k6 (rotor and caliper) , Is it different size than the 77/78 ?? Like will it look weird? Anyone done this for a 77/78 before? Were you able to use another year's brake parts?

Ericcb750 - Just got done adding a dual to a '77k front end. If I remember right the caliper on the '76's were the older style, which take different pads, different size piston and use a different arm (the earlier style arm curved upward, where the 77'-78K's had a straight arm and used the newer style caliper that allowed you to remove the bolts from the front, instead of using an allen socket from behind.)

The older style calipers will fit on the newer style arms but I'd recommend using the same calipers & corresponding arms on both sides.

On the 77-78's, you'll need to modify the speedo plate and the right side rotor. It's best if you can find someone to mill the backside of the right rotor so that the speedo drive plate fits inside. You can use a dremel tool but it looks like crud, and you'll go through a LOT of cutoff wheels. You'll also need some longer rotor bolts (I'd recommend finding some older Goldwing front rotor bolts, because the heads are thin enough to allow clearance for the speedo drive.)

Eydugstr · « **Reply #10 on:** July 10, 2014, 01:52:33 PM »

Here's a link that might help about the rotor/speedo drive modification - http://forums.sohc4.net/index.php?topic=121495.msg1377016#msg1377016

scottly · « **Reply #11 on:** July 10, 2014, 07:45:59 PM »

All of the K rotors are the same, but the K7/K8 calipers have 42.8mm pistons, while earlier K models have 38mm pistons. While you could mount an earlier caliper with it's matching swing arm on one side, it would certainly look odd.

exf5003 · « **Reply #12 on:** July 11, 2014, 06:26:33 AM »

Not trying to hijack your thread, but for those of you who have done dual are you experiencing twice the notorious break squeal now??

flybox1 · « **Reply #13 on:** July 11, 2014, 06:54:45 AM »

Quote from: exf5003 on July 11, 2014, 06:26:33 AM

Not trying to hijack your thread, but for those of you who have done dual are you experiencing twice the notorious break squeal now??

i'm not. good condition, properly configured parts have a lot to do with it.

Ericcb750 · « **Reply #14 on:** July 11, 2014, 11:06:21 AM »

Thank you all very much for all the information. What I will try to do is find parts from another 77/78 to make things the same on both sides. Just so I understand, the Rotors for all the 69-78 750's are the same size? I know some appear to have different "spoke pattern" between the actual disk and the bolts but I have seen a lot that look like the one on my bike now so matching shouldn't be an issue. Sorry for all the questions I just want to make sure that when I buy parts they are going to be correct.

Were any of you able to find the bolts you needed at like a hardware store or do you need the Goldwing bolts specifically ?? I really appreciate all the help guys. Thank you all very much.

flybox1 · « **Reply #15 on:** July 11, 2014, 11:29:55 AM »

my first response has a thread link there with my full parts needed list to order from bolt depot. part no., sizes and all. Those longer rotor bolts you can get anywhere, but, the heads are too tall to clear the speedo drive plate, so some source GL rotor bolts which already have the smaller head.
I just used a rotary tool flap wheel to take them down about 2mm, and then I lightly polished them.
I think they were 110mm. Check the parts list.....

Ericcb750 · « **Reply #16 on:** July 11, 2014, 11:40:51 AM »

Sweet, Thanks Flybox. I'll Check it out, I appreciate it.

Don R · « **Reply #17 on:** July 11, 2014, 08:34:46 PM »

I used 5/16 bolts on the two rotors, not positive on the length. The purists insist on metric but 5/16" are very close to the same size. Get good ones.

75/76 cb750F calipers are center fitting type, same as 77/78K.

Wobbly · « **Reply #18 on:** July 12, 2014, 01:37:13 AM »

Quote

I used 5/16 bolts on the two rotors, not positive on the length. The purists insist on metric but 5/16" are very close to the same size. Get good ones.

I did the conversion with all original Honda parts--which is also the easiest way regarding the speedometer drive, etc.. But since nobody likes to use the search function here, and--out of convenience-a new thread is started every time the same question pops up, such information is pushed aside. Again, the dual disc conversion for the 77/78k has been covered here before in great detail and with lots of pictures.

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Author Topic: 1978 cb750k dual DISK Convert Question (Read 2240 times)

Wobbly

Wobbly