Rear disc conversion

[Spitfire]

Amazing work, how it works is all black magic to me but it is certainly the way to go to make bespoke parts.

Cheers

Denis

[Laverdaroo]

Next time you get the lathe out can you make a short video for us non-engineer types?


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I'd love to but I'm not an engineer, I'm an aquatic consultant but just an addicted shed twiddler. I' make some inroads to havin a go once we move.

[allankelly1]

Yep, that looks much better, great work, nice to see someone thinking outside of the box.

Hi Oddjob

Thanks for the

On a mk3 version at the mo as added an extra lug so the torque arm fitting is just outside the disc outer diameter after looking at some other sets up on the internet and it keeps the torque arm to caliper mounting point as a nice 90degree “elbow”

Also got a couple of rose joints on order so I can make up a nice custom length torque arm from two rose joints, a length of studding and a alloy tube machine to the correct length that slips over the studding so it looks pleasing to the eyes

All is now slowly coming together

Best wishes Al


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[K2-K6]

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Looks particularly neat in this view and almost a standard build.

When modifying in this way it often has impact in that you have to do a double take and ask yourself if that's original or not  very elegant conversion.

[allankelly1]

Hi all

Quick update

Now as I have the final design for the disc carrier have bit the bullet and now made my first aluminium part for this disc conversion project



Also as you can see for the disc carrier assembly I have added a smaller lip seal seal housing that mounts on the main carrier which both housed a shaft lip seal to prevent the ingress of dirt. And due the inner bore of the seal housing being less than the outrigger bearing OD, this seal housing also locks the outrigger bearing in its location bore to remove and possible side float




For the inner side of the disc carrier to increase radial location further, the rear of the disc carrier has a bore that locates on the original machined  OD on the hub boss that carries one of the wheel bearings,

And as you can see below there is also the required inner bearing spacer so that you can tighten up the wheel spindle correctly without placing any side loading on any of the three ball bearing inner race assemblies





Lastly disc bolts on and a spacer fits in the lip seal to keep any dirt out





Then fitted on the bike with an extra dummy 17mm spacer (to represent the caliper hanger thickness) and all looks good. And with wheel spindle tight the wheel and disk revolve as planned



Lastly finally after a few design changes got the caliper hanger right, that now has the required torque arm fitting, and now ordered two rose joints so I can make up the torque arm to length using the rose joints, a length of m8 studding and a nice alloy tube cut to the correct length to cover up the studding






I still have the disc to wheel hub locking part to finish and this is going to be a one piece part rather than four separate posts for strength but the project is making good progress and really happy so far

Next big job is to design and print the disc to hub locker and once this is done and both the disc locker and the hanger are in aluminium that’s pretty well the back wheel assembly complete

Think that’s all for now

Catch up soon

Best wishes Al


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[Laverdaroo]

Simply stunning mate, looks absolutely brilliant and like you said, looks pretty much OE

[allankelly1]

Got torque arm sorted today



And now fitted on

Must admit pretty proud of what has been achieved so far and will leave it to you to decide, but looks factory fresh / OM








Still got to fit the disc carrier locker unit which is now designed in my head and the final design of caliper hanger has now being subbed out to a mate. So going to start work out how to modify the rearsets to take a master cylinder as that is really the next thing to be solved

Catch up soon

Best wishes Al


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[McCabe-Thiele (Ted)]

How do you determine the rear brake pressure on the disk to prevent rear wheel locking up in the dry?

[allankelly1]

Hi Ted

Just need to source the correct Master cylinder bore and any brake system can be made to lock if required

Really it’s just simple hydraulics theory where a for a fixed size caliper piston,  a smaller MC  bore will give more “feel” with more pedal movement to fully apply the brake and a bigger MC bore will give less pedal movement and  “feel” etc due to the different size MC bore and swept volumes

On my Rd like lots of others that have a twin disc 350 we have changed  from a standard 5/8 to a 1/2 bore for the front brake MC cylinder and the change is like night and day even with slightly more lever movement due to the reduction in bore size

Interesting for my twin disc  front conversion I used the original single M/C  from D/S with no problems even though in theory the volume of fluid needed is twice the volume due to the master cylinder now operating two pistons of roughly the same diameter as the original single piston unit

And currently as the Brembo unit is from a cagiva Mito that has the same size disc as currently now fitted to the Honda (226mm) for a starting point have for the time being got the same M/C as fitted to the Mito

Lastly it will also depend on “lever length” for my rearsets conversion to get the correct feel and braking


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[Tomb]

Love this work.

And agree with Allan Kelly, reducing MC piston dia' on some of my old bikes has made a huge difference to braking ability, or the other way round I have put bigger (more pistons) calipers on and reach the same effect. Yes as Allan says, more lever travel, but when doing the mod I upgrade to braided steel hoses and service the brake so no real difference is noticed.

[Bryanj]

Just recently done the rear brakes on a triked GL 1500 which has a "linked" rear brake, front left caliper+rear and with one extra caliper(est 50% extra area) the rear pedal gets a lot more travel and feels spongey but isnt, cant upgrade the master as the consensus is the production line starts with therear master hanging on a piece of string and the bike is built round it!

[K2-K6]

Very good work alankelly1 and seeing it as a whole with the others mods of rims, twins on front, seat etc, it fits in so well on your bike.

Comments on balance of systems, as already noted it's shifting the hydraulic reduction ratio that trims it. Competition car balance adjustment pedal arrangements use a mastercylinder for each the front and rear systems descreet from one another and balanced initially by bore size. Then by moving the fulcrum between the two it can give bias to front or rear depending on driver choice.

For a combined system on the bike, you could use a front mastercylinder (cable operated from pedal and hidden) but with a pass through line from front system that goes in a bespoke cap to reservoir.  This pushes the rear caliper along with the front brakes, but if you use the rear to operate the remote mc it seals the line from the front and just actuates the rear independently.  This is the arrangement used in rally cars for years as hydraulic handbrake setup.

[allankelly1]

Hi K2-K6

Yes know the bias system well as had the same set up when I build my Dax Rush many years ago that has a twin master cylinders for front / rear brakes so you could balance the brake bias front to rear




For the bike just going for a independent rear brake system with a separate master cylinder for just the rear wheel

Much easier to set up and plumb

Catch up again soon and thank you for all the positive comments

Best wishes Al


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[Spitfire]

Glad to hearv that you are balancing the braking, the rear disc on my 750F1 is definately too fierce, it's a better brake than the front one.

Cheers

Dennis

[McCabe-Thiele (Ted)]

I upgraded the rear brakes on my Cooper S back in the 1970,s no dual brake circuits on them at the time - the rear drums would lock up really easily after my rear wheel cylinder upgrade - ended up fitting an adjustable brake balancer to replace the existing fixed one mounted on the rear subframe. Worked a treat.