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There are a number of ways to improve the disc brake on a Commando.
1) Fit a 1/2" mastercylinder from another brand of bike.
2) Buy an aftermarket Lockheed or similar calliper and/or disc.
3) Sleeve your mastercylinder to 1/2".
4) Get a 11mm conversion from the US or a 1/2" sleeve job from
the UK (See the bottom of the page)
I would recommend Vintage Brake
in the US for interesting info, on drum brakes as well.
An approach to 3) follows.....
I need to make a point regarding liability. I am not an engineer.
I have no qualifications or experience of engineering. If you are interested
in following this modification you must get it checked by a qualified
engineer who can certify that it is safe. Do not do it otherwise.
A number of people have been been in touch with me over the last couple
of years in regard to the master cylinder brake modification sleeving
it to 1/2 inch as detailed in Classic Motorcycle Mechanics.
Here follows the simple version...
The original Lockheed master cylinder as fitted to Norton Commandos
from 1972 (and to some Ducatis) was given a 5/8 bore for reasons which
only promote cynicism and do not bear repeating here. The end result
was the brake did not work very well. The lever felt very wooden, and
it was hard to get enough braking from it.
I decided to try and improve the hydraulic advantage by sleeving the
master cylinder down. I had experienced good results with a 1/2 inch
Grimeca cylinder on a Norton so took that size as a reasonable objective.
Having heard of seals from a 1980s Kawasaki GPZ 500 (EZ500 in some
countries) being used for the this purpose I took that as a starting
point. I obtained a M/C from one and drew up a piston which had the
shape and width of the Kawasaki piston but otherwise the length of the
Norton.
Click for larger image
My master cylinder was sleeved in stainless steel. If using SS,
and I would recommend it, the piston should be made from something
hard but not SS. I recommend Aluminium Bronze 3. (As a friend said,
AB3 will still be there when the Vogons invade Earth) Do not use soft
alloys. While they may stand up to the wear inside the cylinder they
will pickup and smear at the contact point with the lever. There is
no reason why the cylinder could not be sleeved in aluminium just as
original, and the piston made in steel. But if you think about it those
materials were chosen for poor reasons and we can do better. Why put
steel in a rust prone environment?
Click for larger printable image of piston design
The piston is a fairly straightforward turning job. The Kawasaki seal
kit number is 43020-1098. This may be an Australian part
number, it's from a GPZ 500 from early eighties, single disc type. In
the US this bike was called an EZ 500.
In the kit you get a piston, seals and spring. Biff the piston and use
the seals and spring. If you need a new boot and spring clip they are
available from the usual sources of Norton parts.
The original cylinder had a trap valve in the same end of the bore to
slow the fluid in the downward direction (ask yourself, why would anyone
make the brake slow to act? No, don't. ) Leave this out. It wouldn't
fit the smaller bore anyway. With this exception, assembling the
brake is exactly as for the standard setup. If anything about your setup
is not standard, for example the calliper, or the lever (any change
to the lever is significant, mail me if you need to know why),
deep thought may be needed.
While I have not struck problems in those I have assembled personally
or heard of any problems with the many assembled to these instructions
elsewhere there is need to be cautious . There are variations to dimensions
in the original casting, for example I am told there is up to 160 thou
difference possible in length of the internal bore. When you assemble
your brake, before you fill and bleed it, make sure the lever can travel
right to the bar.
Mine has now done in excess of 20,000 miles, most in tough city traffic.
It gets a lot of hard use. I dissassembled it recently because the boot
had ripped (it was not renewed when I did the sleeve job) and I could
find no evidence of wear anywhere.
The all up price in Australia is about A$90 for sleeving, $45 piston,
$49 seal kit, a total of less than A$200. About $100US. Cheap
for a good brake. If you are having problems getting your cylinder sleeved
a number of people from around the world have sent their's to the person
who did mine in Sydney. One bloke in the UK got his back in 18 days.The
outfit which does the sleeving does many brake cylinders every day.
Partmasters
attention Terry Milligan
18 Harp St,
Belmore
NSW 2192
Australia,
ph 02 9787 3111
He takes the usual credit cards. I don't mind calling him for you to
let him know you want to send one.
Pistons can be made by...
Alan Graham,
Po Box 92,
Douglas Park
NSW 2569
Australia
(Ph 0246 32 7202)
I don't know whether Alan would want to do business worldwide. I have
no financial interest in these businesses.
Installation instructions
While soaking the seals in brake fluid inspect the piston to see there
are no sharp corners that will cut the seals. Put the seals on carefully,
the main trap is letting the rear one fall into the groove for the boot.
It is hard to get out. I nurse the seals on with a tiny screwdriver
without sharp edges.
Put the boot on the piston in the same way it goes on the original.
Lubricate the cylinder with fluid and carefully insert the piston, careful
with the seals. Before pushing against the spring arrange the boot and
its spring clip in the right place, then push the piston down with your
thumb and prod the boot and spring clip down into place with a screwdriver.
It pays to start the clip by pushing one side down first so it does
not get caught in the slots for the screws that hold the M/C to the
switchgear.
Holding the piston down in place (don't let it pop out, the less you
have to put the seals in and out of the entrance to the cylinder, the
better), put the lever in and let it take the place of your thumb, and
then holding the lever against the pressure of the spring, slip the
bolt into the pivot. Pop a tiny amount of grease on the end of the piston
and you are done...
The modification was printed in Classic Bike Mechanics Oct 1998. The
article included an interesting (and compelling) before and after
comparison test as follows...
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