Twin Disks

[Darkness]

A few questions about going for double disk brakes on the front wheel:

1.  Does an early Goldwing speedo drive just bolt to the hub when the second disk is in place?

2.  Do you know of anyone who can drill holes in disks?

3.  Can you use the same m/c or does the lever travel get huge?

4.  Where do you get longer sholdered bolts to hold both disks to the hub?

Oh, and is it worth the time, cost and effort?

[K2-K6]

My experience was with a 750 K2 so you'll have to judge for yourself the relevance.

With a twin setup using standard parts to match original they were quite potent and would easily howl the front tyre so definitely much more effective than a single, also very good with a passenger/extra kilos.

Mine used the standard master and rubber hoses and had no problems with travel. It makes for a fairly light lever load (for the time) but is much more in keeping with what we are used to now with modern brakes so the ratios seem to stack up ok and I would guess they'd be considered normal if designed right now.

The discs are not too hard to machine if you have the right kit, but the holes are really neat if something like spark erosion is used and look much more like original factory spec.

[Bryanj]

(1) NO

(2) Sorry No

(3) Yes but an early goldwing one is better

(4) Any decent bolt supplier Just make sure they are HT

(5)Depends on how fast you need to stop!

[SteveD CB500K0]

Take a look at Ben's article on twin disc conversion here

[Darkness]

Thanks for the answers Guys:  looks like a little project coming on.......

The link is particularly clear about what is entailed.

I used to think the Honda hydraulic disk was OK provided it wasn't too cold and wet, but I've kind of got used to twin Brembo Goldlines these days!

[Bryanj]

That link is good EXCEPT for the fact it says a standard 500 speedo drive will work NO IT WON'T.

You need a very early, and obsoleted, 750 drive plate or you need to modify the one you have, I have pictures somewhere of the differences but basically you need to remove the outer rim and original drive tangs and then bend the flat plate down over the two flats machined on the hub, sometimes it is necessary to easy the inner hole of the disc carrier so that you end up with a rectangular slot and not a segment of a circle.

[matthewmosse]

I found it was a quite simple job to modify things to get drive to front speedo. It would have been using parts from late 500 and 550k3 parts

[z1100r]

Bigger master cylinder is IMO essential.  The small bored original is not powerful enough.

Didn't have any probs with speedo drive..

Aligning the swinging bracket with the disk is essential. On mine it just meant the mudguard went between the bracket and forkleg. A little odd because on the other side the mudguard is factory bent to fit on the outside of the bracket, but this way meant no filing, perfect alignment, and no flaking of the chrome trying to bend the mudguard. No one has ever noticed.

All done early eighties, using the original MC and bending the front mudguard and filing the brackets.


Restored this year but swinging bracket fitted outside mudguard as i said..... alot easier and swinging arm is better inline with disc preventing squeal. Master cylinder reservoir is bit tall though

[K2-K6]

Just to add a bit of clarity about the master cylinder.

The bore size in combination with the lever geometry will alter the travel and power your hand has when using the brake, the reservoir capacity is a seperate issue and just has to have enough capacity to maintain a supply of fluid to the system as the pads wear and so stop any air entering the system from the top.

If you check the level regularly then you can really use whatever size you feel happy with (look at the tiny pots used on some current bikes with huge calipers).

The bore/piston size of the master-cylinder is a valid way of tailoring the system to your own requirements. Smaller= longer lever travel and reduced hand effort, bigger= shorter travel, more immediate initial bite, but you'll have to put more effort into it to raise the braking level.

The wire guide is a good idea for the speedo cable, but if you get a modern internal wall tie from a builders they are now made of stainless-steel and quite a good guage so even look good when finished.

[Darkness]

Thanks for the further comments Guys.

Brick ties are indeed a good source of stainless wire and pierced flat.

As you point out, lever pressure and lever travel are functions of the ratio of the master cylinder and caliper piston bores, plus the geometry of the lever and its pivot.

That's why I was interested to hear from those who've already done the conversion: no point in re-inventing the wheel [Nor the disks bolted to it!], especially as it's easier to use existing parts rather than designing something from scratch.

 

[Bryanj]

The first twin disc 500 i did hac one caliper in front and one behind as the 550 had not yet come out and i found that with the standard master it worked but had a long travel and just did not inspire my confidence, at the time i worked in a bike shop and bought an early GL 1000 master packaged as a Girling unit (suspect it was a Japanese cosmetic "Second") and it improved markedly