HOW To: twin disk conversion


Excess twin
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Manchester, UK
This is how I did my twin disk conversion on my xs400D.

I first did this on my mag wheels, but when i got the wires, transfered it over to the new wheels.

you will need;

early lower left fork leg with the caliper mounts

A left hand caliper mount from xs750. XS850 XS1100 SR500 it says "L" on it for left, with bolts.

A left hand caliper from the same bikes above (its important you get a left one so the bleed nipple is at the top of the caliper for brake bleeding

new braided hoses

here is the original lengths i used, they are slightly too long, so will be fine for the SE type of forks.


Dual pipe bano fitting for Master cylinder

A master cylinder capable of pushing 2 calipers use xs750, xs850 xs1100 or R1 R6 or what ever you can get cheap. I used the xs1100 as my bike was a restoration and original looks were inportant.

bolts for the disk with locking washers

another disk, either from the xs range. not RD(RZ) as the dishing is different

1) first take your wheel off and prize out the plastic cover. it has the same number of little plastic extrusions that fit into the screw threads, soitcan be a bit reluctant to move

2) check your new caliper and Master cyl for damage and renew seals if in any doubt

3) Mount the master cylinder on the bars

4) put the new disk on the wheel


5) mount the caliper mount using the bolts

6) caliper can then be put on the disk (with pads in of course)

At this stage a had very slight issues with fit. the caliper body was just touching the disk


so i needed to pull the caliper towards the fork leg. I had no issues with the mag wheel and Hornix never reported anything in his conversion so it may be just a one off.

Anyway i took a couple of mill off the caliper carrier using a hand file.


and a little inside the caliper, just to the steel brake pad slider


7) fit the brake lines, being carefull the route/protect them around the headlamp. The dual banjo bolt goes into the master cylinder where the two hoses start.

8) connect it all up

9) I had a lot of issues trying to bleed the brakes, in the end I tie wrapped the lever back and sucked the fluid through a clear pipe to start things off.

10) the conversion was a great success and can out brake the RD/RZ's in a duel i had at the cart track in the UK:thumbsup:
That's great Drewpy :thumbsup:
One question, why do you not take a single line down to the middle of the bottom yoke and use a splitter, that would mean less fluid to move ?
I think it wont't make a difference.
Let's assume that sqeezing the brake lever gives a fluid shift if 10cc. In drewpy's (and mine) setup every line gets 5cc. In your setup 10cc goes to the middle yoke, and then gets split up in 2x5cc. I don't think there's a difference :?

The two disk setup is great. looks great and brakes even better. This is my setup:
Yamaha R6 14mm master brake cylinder (have a matching clutch lever on the left side)
Steal braided lines, ment to be on a Yamaha R1
Left brake caliper of a XJ650.
Left disk is the rear disk of my parts-bike.
Disk mounted with new bolts using locktite instead of those blocking plates.
The disks were glasspearled and I repaint the center using Hammerite.
New brake pads (EBC) finished the job.
I can recommend it to anyone. It's a simple operation since Yamaha had the wisdom of using the same parts on many different models :)
I was looking from the point of view of the quantity of fluid held in the system. Assuming the central point of the pipe run is (say for arguments sake) around the bottom yoke. Your run has two pipes top and bottom, the alternative has one above and two below, that quantity sitting inside waiting to be pumped is 25% less.
I don't really look at modern bikes in showrooms, but I assume the manufacturers use a splitter and just have one pipe from the m/c ?

I'm not saying there's anything wrong with your set-up, (it clearly works fine :thumbsup:) I was just interested to know why do it that way.
there really wasn't room to mount a splitter TBH. I had the one off an XS750 and try as I might, couldn't get it to fit in.

I was restoring the bike as opposed to transforming it so wanted it to look as orignial as possible
all sohc hubs have the holes for another disk. yamaha used that one for the SR range and blanked the opposite side! as far as I know only the 77' and earlier disk brake models had the lower fork legs. Don't know if the SR has the same diameter stancions (33mm) as the xs.

if you have a dohc, the xj range will fit.
Little correction on that one: the SR500 has another rim size: 19 inch.
Before finding the "holy grail xs250 wire wheels" i tried to puzzle out wether a sr500 front hub would fit. Problems are the 17mm diameter of the shaft, XS400 has 15mm and also the hub's disk flanges are too far from eachother. So you have to make the calipers line out properly. Another option is a total fork swap. SR forks are 35mm (xs400: 33mm) and also 7cm (!!) longer. Not a nice view I think ;) So, for a 2 disc wire wheel conversion the only option is finding a set of xs250/360 wire wheels. If you like single disk (off topic) you can try a RD hub.
Hornix, never said the SR wheel fitted the XS, i was talking about the fork stancions but didn't know the size. 2mm isn't a lot so reaming out 1mm can't be hard or dangerous.

7cm longer? you could attach the drop handlebars there:wink2:
Sorry, my bad. Thought I wassa speaking the inglies velly well ;)
But if your yokes are reamed out, the forklegs will still be too close to put a SR hub in. Or am I wrong?
7cm is ehhhm a bit to long to put the forks trought the yokes. Think it is this long because of the off road genes of the SR frame: the XT500.
I lowered my SR 2cm's in the front and mounted 2cm longer rear shocks.
As you can see the jiffy has to grow an inch, I water it every day and a bit of furtilyzer will do the rest :p
awesome job! def a project ill be doing on my '81. sorry if you already asked this question...but what was the approximate cost of the whole project? US dollars if possible.
awesome job! def a project ill be doing on my '81. sorry if you already asked this question...but what was the approximate cost of the whole project? US dollars if possible.

you'll have to cost it yourself as the supply and demand rules apply here.

its finding the parts that's the hardest part.
ok...thanks for fast response...i guess i was just wondering how much it cost you so i could get an average estimate