Author Topic: Twin disc caliper modification?  (Read 1003 times)

Offline SteveD CB500K0

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Re: Twin disc caliper modification?
« Reply #15 on: February 12, 2020, 12:27:49 PM »
I didn’t even know the cunifer was a thing.

Had to Google it


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Offline sprinta

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Re: Twin disc caliper modification?
« Reply #16 on: February 12, 2020, 02:37:09 PM »
The internal dimension of the brake line inlet on the Caliper is identical to bleed nipple inlet except the port to the piston chamber is approx 0.5 mm larger. As Bryan mentions it is not threaded all the way. The thread is 1.25mm pitch.

Photo of the olive below.



(Attachment Link)

Are you indicating that with the 'olive' removed both sides have the same seat face such that the nipple can be fitted to either side without any further modification?

Offline 71 V12

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Re: Twin disc caliper modification?
« Reply #17 on: February 12, 2020, 04:38:46 PM »
Hi Andy,

Visually the inlets look the same. The only difference that I can see is the hole at the bottom of the inlet on the brake pipe side is about 0.5mm bigger than the bleed inlet to allow for the olive insert.

Therefore to fit the olive in the bleed inlet that hole would need to careful enlarged. I guess you would want The olive to be a slight interference fit and perhaps a small tab of thread lock to seal it well.

Having said all of this, I really hope that the pipe will seal with right brake tube nut and OP1 flare.

Online Bryanj

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Re: Twin disc caliper modification?
« Reply #18 on: February 12, 2020, 05:45:41 PM »
Kunifer is way easier to bend, never rusts and seals better as it forms to the shapes better.
The only vehicle i would use original steel on would be a Citroen with hydromatic suspension as they have very odd ends with rubber seals

Offline sprinta

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Re: Twin disc caliper modification?
« Reply #19 on: February 26, 2020, 02:11:34 PM »
I am considering doing a twin disc conversion on my 73 CB750 K2 and currently looking at all the parts I would require to do the modification.

On looking at the caliper whilst it it is straightforward to fit to the RH side they are handed in the sense that the nipple will now be closer to the fork tube and the hydraulic pipe now furthest away as the seats for the nipple and hydraulic pipe are different with the nipple using an inverse cone shape and the pipe a raised cone seat.

On looking at the relevant parts book page, see attached, there is an unnumbered part that looks to be some sort of olive insert above the pipe connection position.

Can anybody advise if this a push in seat that can be removed or if there is a relatively simple process so the nipple and hydraulic can be fitted as a mirror image of the LH side with the hydraulic pipe close to the fork leg?

Removing the 'olive' is fairly straightforward.

The bore of the olive is around 3.2mm dia and as such will take an M4 tap.

After tapping a few threads into the olive it can simply be drawn out with an M4 screw, nut and washers, see attached.

With the olive removed both threaded holes and seats are the same, at least on my caliper. So all that is required is to press the olive into the original nipple bleed hole and the screw the bleed nipple into the original brake pipe position.

Offline 71 V12

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Re: Twin disc caliper modification?
« Reply #20 on: February 26, 2020, 08:40:57 PM »
Neat job Andy.

Any thoughts on how to insert the olive into its new location?

Cheers,

Kevin

Offline sprinta

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Re: Twin disc caliper modification?
« Reply #21 on: February 27, 2020, 01:32:41 PM »
Neat job Andy.

Any thoughts on how to insert the olive into its new location?

Cheers,

Kevin

Not 100% sure at the moment?

Need to put a couple or so more threads in the hole first to be sure the brake pipe flared end will clamp up and seal against the olive face once fitted.

Andy

Offline sprinta

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Re: Twin disc caliper modification?
« Reply #22 on: February 29, 2020, 11:31:13 AM »
Thread just needed cleaning up.

Using the M4 screw just tapped it in and then screwed in the flared brake pipe to fully seat it.

Offline 71 V12

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Re: Twin disc caliper modification?
« Reply #23 on: February 29, 2020, 06:48:31 PM »
Simples, well done👍👍👍👍

Offline sprinta

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Re: Twin disc caliper modification.
« Reply #24 on: April 19, 2020, 06:54:04 PM »
Part 1.

Have now sourced all the parts necessary and completed the twin disc setup.

I had picked up a NOS disc sometime ago and always wanted to do the twin disc setup, as much because I think it looks more balanced but also as I do use all my bikes the single disc quite frankly is very poor.

A number of the parts were used were from a GL1000, longer disc bolts, speedo drive and speedo drive chrome plate.  I decided on the GL1000 route because I thought it was a neater way to do it and it looked more original with the chrome speedo chrome plate. However, the GL1000 speedo drive does require some modification.

The caliper and mounting brks were also used parts which have been modified and refurbished with painting and plating as necessary.

The caliper fork mounting brk aligns correctly and does not require any removal of metal from either the fork or brk lugs. The bottom brk lug aligns but appropriate spacers need to be made for the top two lugs. I removed the lugs from the brk that were not required and the top rear lug has to be removed as it fouls directly against the wheel rim. 

Having reached the photo attachment limit I have continued in the next post.

« Last Edit: April 19, 2020, 07:47:46 PM by sprinta »

Offline sprinta

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Re: Twin disc caliper modification?
« Reply #25 on: April 19, 2020, 07:26:39 PM »
Part 2.

I used an original hose brk and removed the hose 'crook' and re-attached it by 180 deg's so that I could use the same brk on both sides for symmetry. I found the std brake hose a bit too short but had a Kawasaki Z900 A4 hose which has the same fittings but was a few mm's longer. (there would appear to be two lengths of the Z900 hose one is the same length as the CB750 and one is slightly longer)

A new solid brake pipe was formed and the ends flared.

Routing the hose requires a bit of faffing around as you have speedo cable, tach cable and the horn to miss when the forks compress in use. Being able to use the steering lock can also be compromised if you are not careful.

It has all installed without too much hassle but it will be necessary to have to remove the whole RH caliper and brk assy in order to remove the front wheel, which hopefully will only be when the tyre needs changing?

Have not had a chance to try it out due to the lockdown and now doubt I will have brake squeal in stereo but hopefully there will an improvement in the braking, if not it looks nice and to my eyes more balanced.

I am currently using the original master cylinder and will evaluate after some use as to if one with a larger piston is required. 
« Last Edit: April 24, 2020, 10:56:34 AM by sprinta »

Online Lobo

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Re: Twin disc caliper modification?
« Reply #26 on: April 19, 2020, 11:36:14 PM »
Nice looking job Sprinta.

... I’ll be interested to learn if the braking is 2x improved. My K2 stops like a pig (even with sintered pads) ... it takes a lot of effort at the lever. If the (original?) master cylinder pressure output is effectively halved as now supplying 2 brakes, are you actually better off? This is doing my head in!

Offline sprinta

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Re: Twin disc caliper modification?
« Reply #27 on: April 20, 2020, 09:59:22 AM »
Nice looking job Sprinta.

... I’ll be interested to learn if the braking is 2x improved. My K2 stops like a pig (even with sintered pads) ... it takes a lot of effort at the lever. If the (original?) master cylinder pressure output is effectively halved as now supplying 2 brakes, are you actually better off? This is doing my head in!

Thanks Lobo.

Hopefully it should improve the braking. I have a Suzuki GT750 and Kawasaki Z900 A4 with twin brakes which both have significantly better braking than the single disc of the CB750, though nothing compared to modern brakes.

I should have included that currently I have not change the original master cylinder.

As you have eluded to, it is not always necessary. Once I have had a chance to use and evaluate the new twin disc setup I will decide if the master cylinder needs replacing as well for one with a larger piston size?

Offline Arch stanton

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Re: Twin disc caliper modification?
« Reply #28 on: April 20, 2020, 01:56:11 PM »
Please excuse my jumping in.
Many years ago. I converted my F1 to double disc. But kept the original master cylinder. But the lever was nearly at the bar, way too soft. Without much feel to it.
So I changed it for a GL1000 item. Much better by far.
I am using that very same front end in my current K1.
It does the job.

Offline 71 V12

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Re: Twin disc caliper modification?
« Reply #29 on: April 20, 2020, 05:05:36 PM »
Well done Andy,

That looks very tidy, nice job👍👍 I agree with your comment about the symmetry, does look better.

Do you have the part number for the GL1000 disc bolts? I guess they are available from DS? Good tip on the flex hose as well.

Need to get back to mine when I complete the huge list of DIY projects currently taking priority.

Let us know how effective the conversion is.

Cheers,

Kevin

 

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