Author Topic: Rear disc conversion  (Read 10089 times)

Offline allankelly1

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Rear disc conversion
« on: October 11, 2021, 01:45:35 PM »
Hi all

As some of you know my rear drum has developed a crack that renders it either scrap or look to a possible repair.




Bike was never going to be standard / original, so now looking to see what is involved in conversion to a rear disc and thought I would do a thread about how I did the conversion unlike when I converted the front end to dual disc




First thing I needed to do was suss out a way of fitting a “disc carrier” that fits the standard hub to see what design was needed.

Spent some time yesterday modelling up a simple dummy disc carrier unit in 3d so I could then overnight print  and then dummy up the build on the bike just to see how it all fitted together and from first dry fit it looks good.

This is the 3d printed disc carrier in ABS.




And this is how it all fits together on the wheel and bike.







The final carrier itself will be machined from a solid aluminium billet and will be designed to lock the carrier in the internal bore so that it is solidly held in place to prevent sideway movement and other features such a extra bosses to lock it in place using some of the internal hub features to prevent possible rotation under braking (and also a oil seal like the sprocket side to prevent water entry to now exposed wheel bearing as the end spacer / boss you see on the dummy disc carrier will be a separate part the final disc carrier will revolve round this spacer)

But for now I am happy with the overall shape and size / distance of the disc from the swing arm and there is plenty of space to add a caliper hanger etc

The next stage will be to source a caliper and then design a caliper mount to suit my chosen unit to mount the caliper on the disc and use the original torque arm mount with a new torque arm arrangement

Again this will be modelled and printed so I can first test fit my design

Then the final stage will be how to convert my rear sets to operate a remote master cylinder

Once these three parts of the design are finalised I can then commit to the final parts in aluminium and then fit

Will update as thing go

Catch up soon

Best wishes Al


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« Last Edit: October 20, 2021, 11:23:46 AM by SteveD CB500K0 »

Offline allankelly1

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Re: Rear drum conversion
« Reply #1 on: October 11, 2021, 04:10:44 PM »
Hi Oddjob

Thanks for the compliment it means a lot

Yes there is some better discs out there but wanted to at least keep the period look and avoid modern discs at the expense of a bit of extra stopping power

It’s a  summer bike anyway and there are better pad materials these days. And can always drill the period discs to improve things without making it look too modern

But I do have a spare twin piston rear  brembo caliper in a box




So may machine off the logo and paint it black to hide its a modern unit but will need to tweak the disc size diameter to suit as its for a smaller disc

It’s early days yet and plenty of time to play around with different ideas but at least  the disc idea looks possible

Catch up soon

Best wishes Al


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Offline allankelly1

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Rear drum conversion
« Reply #2 on: October 11, 2021, 04:45:58 PM »
Hi Oddjob

The cb400n super dream disc I am planning to use is a standard 5mm thick (the one in the pics is an original CB400F front disc that I just had in a box as awaiting the cb400n disc to arrive ), so suits the Brembo unit nicely and just need to reduce the disc diameter by 20mm so the Brembo pad with of 30mm uses the whole disc face as the original cb400n disc has a pad width of 40mm. So the Brembo pad would leave a 10mm unused section on the inner most section of the disc working face


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« Last Edit: October 11, 2021, 04:58:11 PM by allankelly1 »

Online K2-K6

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Re: Rear drum conversion
« Reply #3 on: October 11, 2021, 05:31:22 PM »
Nice work and interesting project, good to see work as it progresses.

A thought though as to design. Have you considered that the disc may need an outrigger bearing? The original brake shoes ordinarily sit equally over the existing wheel bearing (well technically the braking surface of the drum does) to distribute braking torque equally when applied.

The disc arrangement in mock up appears too far out to use that alignment and as I understand the description to centre the assembly into the existing hub which may not be "ahem" symmetric. In other words, as brake is applied it could try and "corkscrew" for want of a better word, the assembly out of the hub. Any failure there ultimately could lock the wheel. It's not a natural torque application line as I view it.

Offline allankelly1

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Re: Rear drum conversion
« Reply #4 on: October 11, 2021, 05:41:54 PM »
Hi K2-k6

Yes there is plenty of room to add a bearing to the disc carrier and good idea

I will at some point add a bearing location as part of the seal arrangement as there is plenty of space

Also I could use an angular contact bearing rather than a normal single race ball bearing so as well as supporting axially the disc carrier it is also held in place radially too for any type of loads / forces

Food for thought

Thanks  for your input and ideas

Best wishes Al


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Re: Rear drum conversion
« Reply #5 on: October 11, 2021, 06:38:38 PM »
Thinking with more clarity  ;D it's a necessary part of design to have a bearing in that location.

The drum brake plate is static and so pinches the main wheel bearings on their inner races when the axle is tightened,  but with the disc "plate" spinning with the wheel you have to go through it in it's entirety (bearing inner race, plus spacer if needed) to complete that clamping requirement while the plate revolves with the wheel.

Without it you couldn't tighten the wheel.

Offline allankelly1

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Rear drum conversion
« Reply #6 on: October 11, 2021, 06:44:29 PM »
Yes the bearing set up will need some thought but it’s simple to add two bearings in to the disc carrier to give the correct support

Next job though is to get the correct cb400n disc in place and design and print a caliper hanger that fits the Brembo unit

Once this is sorted in rough I can then review the final set up and add the finally touches to the final assembly such a extra bearings and spacers and then make the final unit in aluminium

And the great thing is that 3d models take out all the guess work like when I built up my one-off front end for my hybrid build






A lot of work but a nice special one off

Best wishes Al
« Last Edit: October 11, 2021, 08:46:10 PM by allankelly1 »

Offline allankelly1

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Rear drum conversion
« Reply #7 on: October 11, 2021, 07:52:52 PM »
Thinking with more clarity  ;D it's a necessary part of design to have a bearing in that location.

The drum brake plate is static and so pinches the main wheel bearings on their inner races when the axle is tightened,  but with the disc "plate" spinning with the wheel you have to go through it in it's entirety (bearing inner race, plus spacer if needed) to complete that clamping requirement while the plate revolves with the wheel.

Without it you couldn't tighten the wheel.
Hi K2-K6

Just been thinking and if I add two bearings like the wheel bearing set up with a spacer tube etc on the disc carrier that will solve the possible sideways movement as the unit would be clamped in place by the wheel spindle like the wheel itself And to stop any rotation movement just need a set of bosses on the end that snuggly fit between the Cush drive  bosses cast on the inside of the hub assembly

May also add a rubber some rubber dampers to stop any possible rattles due to slight movement of the disc carrier in the wheel hub  (like a cush drive) as I can print custom rubber inserts

Easy peasy and the design means I don’t need to do any mods to the original hub itself

Just waiting for that disc to arrive now so I can sort out that caliper mounting

Lastly just need to decide a price on my original complete kick starter that I no longer need due to the rearsets and thats the project financed




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Best wishes Al
« Last Edit: October 11, 2021, 08:03:22 PM by allankelly1 »

Offline Laverdaroo

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Re: Rear drum conversion
« Reply #8 on: October 11, 2021, 08:38:18 PM »
Well that's p@*sed on my chips for sure ;D ;D ;D


I'm in utter awe of what you can do and have achieved on the computer and printer, what a superb way to go at things, fantastic work. I was really chuffed 'fasion-ing' a bespoke reg plate holder n bracket  for the 400, I feel totally 'top trumped' LOL

So far that's a great start to a solution and fining the read really helpful as I wanted to do similar with the one I have ready to start in the shed, (currently parts collecting). Huge food for thought and a great topic. Keep us up to speed on how you're getting on.

Skills!!!

PS:- Im with Ken, dont 'diss' Brembos' ;D
Mornings are the invention of the devil!

1977 CB550F (current money pit!!)
2002 VFR800 VTEC (The Beloved)
1977 CB400F (the last money pit!)
1998 Ducati 748\853 conversion(sold :()
1980 ish CB750KZ in a billion bits (need to get rid, anybody want one?))

Offline allankelly1

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Rear drum conversion
« Reply #9 on: October 11, 2021, 08:55:16 PM »
Hi

Thanks for the compliments and point taken  on the wanton vandalism of the Brembo caliper

I think when it’s all done, as I will have the models of all the required parts, I am happy to share any engineering drawings etc as I guess other would like to maybe do this change but would need to farm out the machining side of it as I have plenty of other projects on the go as I print lots of other NLA parts for the RD guys as a “hobby”




On the other hand if I win the lottery I will have my own machine shop with a CNC mill lathe etc and I will do your conversion for free


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« Last Edit: October 11, 2021, 09:18:36 PM by allankelly1 »

Offline Laverdaroo

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Re: Rear drum conversion
« Reply #10 on: October 11, 2021, 09:54:14 PM »
Love it :o

I saw your RD horn bracket on your 400, I think it was you wasn't it? Looked brilliant and I clocked that you'd said you printed it. I was in the LC club for a while, had a belter of an LC but sold it to pay the rent one month :-[ :-[ :'(    as you do!

If only we'd had these printers back then i could have printed some gold to buy more pistons for it, it was ace ;D
Mornings are the invention of the devil!

1977 CB550F (current money pit!!)
2002 VFR800 VTEC (The Beloved)
1977 CB400F (the last money pit!)
1998 Ducati 748\853 conversion(sold :()
1980 ish CB750KZ in a billion bits (need to get rid, anybody want one?))

Offline allankelly1

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Rear drum conversion
« Reply #11 on: October 11, 2021, 10:02:19 PM »
Yes that was me




Always loved the that part of the 350lc


 
It was a classic bit of style

And just had to have it on my CB400F

Just had to print a bespoke horn cover to suit like you do

Best wishes Al


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« Last Edit: October 11, 2021, 10:04:05 PM by allankelly1 »

Offline Laverdaroo

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Re: Rear drum conversion
« Reply #12 on: October 11, 2021, 10:28:27 PM »
 :o "Stone him!"

Don't listen to the nasty man ;D
Mornings are the invention of the devil!

1977 CB550F (current money pit!!)
2002 VFR800 VTEC (The Beloved)
1977 CB400F (the last money pit!)
1998 Ducati 748\853 conversion(sold :()
1980 ish CB750KZ in a billion bits (need to get rid, anybody want one?))

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Re: Rear drum conversion
« Reply #13 on: October 11, 2021, 10:29:59 PM »
"Hi K2-K6

Just been thinking and if I add two bearings like the wheel bearing set up with a spacer tube etc on the disc carrier that will solve the possible sideways movement as the unit would be clamped in place by the wheel spindle like the wheel itself And to stop any rotation movement just need a set of bosses on the end that snuggly fit between the Cush drive  bosses cast on the inside of the hub assembly

May also add a rubber some rubber dampers to stop any possible rattles due to slight movement of the disc carrier in the wheel hub  (like a cush drive) as I can print custom rubber inserts"

Yes that's how I see it as the disc plate virtually running autonomously on it's own bearing set around the axle and taking drive as you say from the wheel to transmit torque from one to the other. A little less demanding than sprocket as it's only got to resist torque one way, as opposed to drive chain with both power and engine braking effects, but would make civilised  :) job of it with some rubber for just a small amount of compliance to remove any clatter.

Are you intending to put the caliper hanger on the spindle to, in place of the outermost spacer? An under slung one could just link straight to the torque arm then.

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Re: Rear drum conversion
« Reply #14 on: October 11, 2021, 10:34:00 PM »
To add, there's some interesting double row wheel bearings used in front wheel drive car rear wheel stub axle location that may be of interest as a single ready made easily available unit that seem to have the right potential dimensions.

 

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