T140 / TR7V Front Master Cylinder Overhaul
Servicing hydraulic brake systems can be rather daunting but the reality is
that they are pretty simple. It is important to ensure cleanliness when working
with all components and not to be heavy handed when loosening and
tightening bleed nipples which can easily snap off.
Prepare by wiping off all dirt
around the master cylinder and
hose joints. Take particular care
around the master cylinder cap
and caliper bleed nipple.
The patient!
Brake fluid is not kind to
paintwork and even with the
greatest care some might
splash. Cover over the fuel tank,
mudguard stays and all other
painted areas with plenty of cloth
or even better plastic sheeting.
Start at the brake caliper and remove the 2 small bolts
that hold the chrome cover on the caliper. If you have not
opened the bleed nipple for
some time then
it is wise to
ensure that it
will open
before
attaching a
hose. That way
you get
unfettered
access with the spanner and can
see clearly what is happening. Use
WD40 if it is tight. Have patience as
if the bleed nipple snaps off then
the caliper could be a total loss.
Set up for bleeding
TOMCC Peterborough
Fix a rubber pipe to the bleed
nipple, preferably clear so you can
see the movement of fluid and air.
The bleed nipple on my caliper is
quite wide so I had to use a short
piece of wider pipe as a bridge to
the special purpose one way brake
bleeding pipe. Open the bleed
nipple and gently pump the brake
lever to push the fluid out. Note that
you don’t need to remove the
master cylinder cap yet but if you
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T140 / TR7V Front Master Cylinder Overhaul
have then pump slowly as the movement of brake fluid in the reservoir can
result in splashes over the bike.
If fluid will not drain then try bleeding the fluid using the close nipple, pump
brake lever, open nipple, hold brake lever to
handlebar, close nipple method (see separate
Mechanics article “Bleeding Brakes”).
When no more fluid can be drained, carefully
remove the master cylinder cap. It should be
empty or thereabouts. Use suitable paper towel
or cloth (that won’t leave fluff behind) to mop out
any remaining
fluid.
Remove the single nut and bolt to remove the
brake lever and plunger. Thoroughly clean
the plunger and spring. Lightly grease to
protect from corrosion and put to one side.
Remove the 4 Philips screws at the rear of
control unit. These are thin and have a habit
of corroding into the housing so if they won’t
move then be patient and ensure that the
Little wonder that this screw
needed persuasion to come out!
screwdriver fits well so as
not to ruin the screw head.
An impact driver is ideal in
these situations and I had
to resort to mine, with
success. If all goes
horribly wrong then drill off
the head and remove the
remaining screw once the unit is apart. Take care when the unit is apart so as
not to put undue strain on the wiring and connections to the switch
mechanism. These will be old and can break easily.
TOMCC Peterborough
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T140 / TR7V Front Master Cylinder Overhaul
Now to take the master cylinder apart. To remove the master cylinder
reservoir, remove the nut and washer
inside the reservoir and lift off. There
will be a smear of brake fluid on both
the reservoir unit and hydraulic
mechanism, so clean this off. The O
ring underneath the reservoir will need
to be replaced. Note that if all inside
looks clean you could leave the
reservoir in situ but you won’t be able
to clean the unit quite as effectively,
and if the unit has not been apart for
dome time then you might as well
renew all seals at the same time.
Ensuring clocks and top of forks are protected; undo
the hose from the master cylinder. Mine was tight so
I ended up attaching the master cylinder back onto
the handlebar to hold it still (I’d hoped that I could
hold the unit away from the bile when I released it,
but best made plans and all that!)
To give parts a thorough clean you’ll
want to split the master cylinder
mechanism from the control unit. It is
important that the unit is reassembled
in the correct position so it is a good
idea to make a note of the number of
threads showing so you can
reassemble without worrying about the
protracted process prescribed by
Triumph which I found difficult to
achieve. If you want to see what I mean
then flip forward to the reassembly.
Remove the single screw that threads
through the rear of the control
unit and acts as a locating pin
for the master cylinder
mechanism. Now you are able
to unscrew the cylinder from
the switch unit. Mine was very
tight and needed heat and
careful force. Again, luck was
on my side and all came off
well.
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T140 / TR7V Front Master Cylinder Overhaul
To take the cylinder apart,
remove the rubber dust cover,
then using the plunger depress
the piston and remove the circlip.
Mine was utterly filthy and gunge
needed to be removed before
circlip could even be seen. The
piston came out with horrible
detritus on it – this overhaul was
well overdue! The piston should be
pushed out by the spring, but my
cylinder barrel had so much
corrosion that I needed to scrape
clean the inside walls before
plunger would come out.
Note how the rubber seal on the piston is fitted and
remove the old one. All rubber components, the
thin washer and the check valve (at the opposite
end of the spring to the piston will all be replaced
and should be in the repair kit.
Note to save money get a repair
kit for a Triumph 2000 clutch
master cylinder. Clean the
plunger and cylinder thoroughly
(I used my Ultrasonic cleaner).
The dirty components
TOMCC Peterborough
The contents of
the overhaul kit
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T140 / TR7V Front Master Cylinder Overhaul
Components after cleaning in the hydrostatic
cleaner. Note that the check valve and
washer were replaced with new items
When cleaning the cylinder
barrel take particular care to
ensure that the groove for the
circlip is clean and that
absolutely no residue is left
behind after cleaning.
As is often the case
assembly is the reverse of
disassembly. Lubricate the
rubber seal that sits on the
piston with clean brake fluid
and taking care to ensure
that it is the right way around
replace it. Fit the new check
valve onto the spring, and with the tiny plastic
spring retainer and primary seal (open end towards
the spring and lubricated with clean brake fluid) refit
the spring assembly into the cylinder. The thin
piston washer follows, inserted with the dished side
facing towards the primary seal. Now insert the
piston, taking care that the seal enters the cylinder
smoothly and again use the plunger to depress the
piston so that the circlip can be refitted. Fit the new
dust cover.
The cylinder can now be fitted to the switch
housing. Hopefully you counted the number of
threads and can set it back in the position it
was. There is a factory process to test the
function of the cylinder mechanism which is
detailed in the factory workshop manual and
is beyond the scope of these articles. Refit the
locating screw.
Attach the brake hose to the
cylinder. Then replace the
reservoir, ensuring that the new
seal is correctly seated on the
underside and that it is at the
correct angle (leaning towards the
brake hose) and tightening the nut
to a torque of 4 to 7lbs ft (6 to 7
Nm).
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T140 / TR7V Front Master Cylinder Overhaul
Finally, reattach to the handlebar and the
other half of the switch housing and if not
done so already (by following the factory
process) the plunger and lever.
Check everything over, and then refill with
the correct new brake fluid. Bleeding the
system will be necessary and is covered by
another article ‘Bleeding Brakes’. Be very
careful to not jerk the brake lever and force
the fluid to splash over any exposed
paintwork.
The new rubber diaphragm needs to be
flattened before replacement, and there
should be a paper washer inside the
reservoir cap.
Note the paper washer in the
reservoir lid, and how the
diaphragm is flattened before
fitment
Pay particular care to ensure that there are
no leaks at joins and ride gently the next
time out.
When I rebuilt my reservoir I found the
brake to be sticky. I hadn’t known the
significance of the setting of the master
cylinder mechanism into the control unit and simply fitted it in. The first time
out the brake was very sticky so I stripped and checked the unit and used
Triumph’s process to set the master cylinder mechanism into the control unit. I
was not convinced that I’d got it right, and sure enough it was still sticky, but
not as bad. I removed the four control unit screws and the locking screw,
rotated the control unit a turn out and all was good.
Now for the ‘Don’t sue me’ part.
Please be aware that this document and its content are provided for your use and
enjoyment. Whilst the author and other members of the TOMCC have created it to
be as accurate and helpful as possible it is no substitute for practical experience,
factory training and a quality workshop manual. Use of this document therefore
carries no warranty whatsoever. Shit happens to all of us when working on bikes so
if it goes wrong in any way then please don’t blame us.
Finally, do be aware of safe practices in the workshop. Don’t blame us if you get
hurt doing anything daft.
Sorry, but in this litigious age it has to be said.
Happy spannering!
TOMCC Peterborough
March 2014
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