Topic: 1975 CB750F - rear brake disc

[macvit7906]

Working on a custom project and I need a rear brake disc that has a smaller diameter than the stock 1975 CB750F rear brake disc. Stock diameter is 296mm, i need something around 260mm.

Does anybody have a source that makes custom brake discs?

Or does anybody know of any other model motorcycles/years that have smaller brake rotors but will fit the bolt pattern of a 75 CB750F rear hub?

[Tugboat]

Dunno if the bolt patterns are the same, but I'm pretty sure CB550/500 has a slightly smaller disc.

[slikwilli420]

Tug is on to something. A 276mm 550 front could be bolted to an F rear carrier IF the bolt pattern is the same. Doesn't get you all the way there but close.

[scottly]

It looks like the rotor carrier is different on the F rotor. However, the rivet pattern might possibly be the same?? If so, you could drill out the rivets and mount the 550 rotor on the F carrier.

[bryanj]

This might be a daft question but as you want a smaller one why not get it turned down

[Bankerdanny]

Tug is on to something. A 276mm 550 front could be bolted to an F rear carrier IF the bolt pattern is the same. Doesn't get you all the way there but close.

I'm not near my bike right now, but I am 99% sure that the bolt spread on the rear rotor is much larger than on the front.

[macvit7906]

Thanks all

1. did some research and unfortunately the bolt patter on the CB750F rear hub is larger and wont fit with a CB550 front disc.

2. If i just have the stock brake disc turned down then the pad track width on the actual rotor becomes too small for the caliper to safely clamp


Anyone ever have a custom brake disc fabricated?

[754]

 Sounds like you need a carrier made to fit an existing disc.
 I have made them but not equipped to do so at present.

 For light use , like lower hp, you can adapt a front wheel with ribbed hub, your disc will bolt on. Then you have to mount a sprocket and spacers easy if you can live without a cush drive. .
 The first F disc hubs are way over built for bike use, everything is smaller , lighter now.

[bryanj]

If you fit a smaller disc the pads wont fit either, the caliper doesnt miraculously move because you fit a different disc, i sortof assumed you already sorted caliper

[macvit7906]

If you fit a smaller disc the pads wont fit either, the caliper doesnt miraculously move because you fit a different disc, i sortof assumed you already sorted caliper

Sorry -  I should have noted I'll be running an aftermarket rear caliper and custom machined caliper bracket that I'll have machined.

Because of the rear tire size im using, the stock caliper (with the caliper bracket arm attached at the front of the swing arm) no longer fits.

[Bankerdanny]

Wouldn't it be much easier to fabricate a new caliper locating arm?

[macvit7906]

Wouldn't it be much easier to fabricate a new caliper locating arm?

Very true - that's the back up plan.

I have a very nice ISR 2 piston rear caliper I would like to try to make work (purely for aesthetics) first

[scottly]

I don't understand, you want a smaller diameter rotor, but a smaller diameter rotor won't work with the caliper you want to use?? What is an ISR two piston caliper? Got pics?

[macvit7906]

I don't understand, you want a smaller diameter rotor, but a smaller diameter rotor won't work with the caliper you want to use?? What is an ISR two piston caliper? Got pics?

Sorry' I'm being confusing. The ISR caliper I want to use will not work with a brake disc diameter larger than 280mm, therefore I cannot use the stock disc.

Because of the rear tire size I'm using I can't use the stock caliper because the bracket linkage wont fit. I could fab up a new linkage but I'd like to see if I can get the ISR caliper to work - it's so much better looking.

Now if I want to make the rotor smaller and change the height of the caliper, I'll need to machine a bracket. I'd like to challenge myself to get it all to work.  Here is a pic off of a dealer's website that sells them from the UK if anyone is interested

[scottly]

Well, like I mentioned before, you *might* be able to drill out the rivets and mount a 276mm 550 rotor on your F rear carrier, or hub. The pattern for the 550 rivet holes is the same as your front F rotor, so you can use that to compare to your rear.

[754]

The F  disc  for wire wheel bus an outdated big hole rotor and ultra heavy hub, anything is a far  better choice. .
 I think ISR makes the Sprotor setups..

[scottly]

The center hole of the rear aluminum carrier looks to be much larger, but the ID of the stainless rotor may be the same?

[Rookster]

        Sorry' I'm being confusing. The ISR caliper I want to use will not work with a brake disc diameter larger than 280mm, therefore I cannot use the stock disc.       

The caliper doesn't care what diameter the disk is.  Just because ISR says you can't exceed 280mm doesn't make it fail if the disk is 296mm.  The only thing that matters is that the pad surface contacts the disk surface without running off the edge or hitting the carrier bolts or rivets.

Scott

[bryanj]

With all you have written easiest answer is turning the disc you have down if it fits in the lathe it can be turned

[low-side]

I agree with Bryanj.  It sounds like the best solution is to get your rotor turned down and fab a bracket that clears everything.  Modifying your existing rotor will take a lot less time and cost a fraction of what a custom one would (assuming you can find someone who would make it).  Sounds like a fun project, good luck with it.

[BenelliSEI]

EBC makes a floating disc, for the rear. Also, can anyone confirm it’s the same as the rear disc on a ‘75/76 GL1000? Looks identical.......

[Bankerdanny]

EBC makes a floating disc, for the rear. Also, can anyone confirm it’s the same as the rear disc on a ‘75/76 GL1000? Looks identical.......

The whole rear disk assembly (including the master) from the 75-77 Goldwing is the same as the 750F. The 75-76 F uses a different caliper setup, but the 77-78 F moved to the floating caliper setup that the GL used and I can tell you from personal experience that the F2/3 caliper and bracket work just fine on the F0/F1.

[754]

 Here is a rotor I cut down  a while ago and madevtte brake hanger for.
 Did it for a buddy at his shop.
 Cut down disc and notched it.

[macvit7906]

Here is a rotor I cut down  a while ago and madevtte brake hanger for.
 Did it for a buddy at his shop.
 Cut down disc and notched it.

Nice work. That's exactly the type of hanger I'll need to make

[754]

Scott. Aka Scottly on here, might be able to help..
 Volunteering for other people, is what I do sometimes..lol..