PTEN_0821 - 36

TOOL BRIEFING
circuit causes the pedal to sink is the
bad guy.
We had a Ford Escape in the shop with
a low brake pedal concern. The pedal
was up high and hard when blocking
off the ports on the master cylinder and
the HCU. We removed the HCU blockers
one at a time and discovered that the
pressure loss was in the circuit feeding
the left rear wheel. We then removed the
rubber brake line from the caliper and
blocked it. The pedal was still mushy.
We removed the steel line from the rubber
hose and blocked it. The pedal came
right up to solid. The causal part was the
rubber brake hose. Under close examination,
we found a soft spot in the hose
that was ballooning under the pressure of
brake activation. Maybe we should have
found this during the visual inspection,
but using the blockers took us straight to
the problem.
The outlet lines on a HCU are usually
very close together and hard to get
a wrench on. Consider using a flare nut
crowfoot set to remove the lines. A crowfoot
enables the removal of a single line
without having to remove others to gain
access. The Sunex 9710M is a nice affordable
3/8 drive crowfoot set. They're small
enough to fit between the lines, leaving
enough room to get a good turn on
the fitting.
USE A PRESSURE BLEEDER
AS A DIAGNOSTIC TOOL
A stuck open outlet valve isn't the only
way that a HCU can affect brake pedal
feel. A stuck closed inlet valve will produce
a brake pressure differential concern
causing a hard pedal and a possible
brake pull. The best piece of equipment
to diagnose a brake pressure differential
concern is a good brake pressure bleeder.
A brake pressure bleeder keeps consistent,
adjustable pressure on the brake
system. This enables you to check pressures
at the wheels, knowing that pressure
at the master cylinder is persistent.
A pressure bleeder allows you to open a
bleeder valve and just let it flow. This is
great when replacing brake lines. You can
push all the air out of a line with just one
turn of the bleeder valve.
There's no need to purchase an expensive
electric or pneumatic pressure bleeder.
I've been using the Mityvac MV6840
hand-pumped pressure bleeder. The unit
keeps a constant 30 psi on the system. It
comes with adapters for most master cylinders,
including a universal adapter that
easily attaches with a chain. Leaky adapters
can hinder your diagnosis and make a
mess on your shop floor. I haven't had any
issues with these adapters leaking.
You'll have no pressure at the wheel
most of the time when an inlet valve is
stuck in the closed position. I have seen
fluid sneak past a stuck valve. So reduced
pressure at the wheel could also be due
to a stuck closed inlet valve in the HCU.
USE THE RIGHT EQUIPMENT
TO BENCH BLEED A
MASTER CYLINDER
Since we're talking about bleeding brakes,
I'd like to emphasize the importance of
using the correct equipment to bench
bleed a master cylinder. One-way check
valves are the gadgets that separate a
good master cylinder bleeder kit from
a bad one. We all know the basic master
cylinder bench bleeding drill. Hoses are
attached to the outlet ports with a threaded
fitting, and the opposite ends of the
hoses are submerged in brake fluid. As
the piston is applied, fluid and air exit the
master cylinder, fluid is sucked back in
when the piston is slowly released. The
problem is that air is also pulled back
into the master cylinder bore during
the backstroke.
The one-way check valves are placed
in line between the threaded fittings
and the hoses. They allow fluid and air
to exit through the hoses while stopping
anything from returning. The
clear hoses allow you to see when the air
bubbles stop, and only fluid is leaving
the master cylinder. Thexton makes a
variety of good master cylinder bleeding
kits. The right kit for you depends on
which adapters you need for the models
you service. They all come with check
36 PTEN AUGUST 2021 www.VehicleServicePros.com
p Figure 2 - Image of blockers being used to
diagnose an HCU.
p Figure 3 - Bleeding a master cylinder using a
bleeding kit with one-way check valves.
valves and tough clear hoses. Be careful
that you don't run the reservoir dry when
using check valves. Keep in mind that no
fluid is getting pulled in to replace what
you pushed out.
BUY EQUIPMENT
YOU CAN TRUST
The steadfast rule in all automotive
diagnoses is if you can't trust the equipment,
you can't trust the results. Take
the extra time and spend the extra
money to get the tools you know you
can count on. You'll surely see a high
return on investment.
ROY RIPPLE is a Ford Senior
Master Technician and an ASE
Master Technician with over
30 years experience in the
automotive industry. He works
full-time as the shop foreman at a Ford
dealer in New Jersey.
ripkrypton@gmail.com
http://www.VehicleServicePros.com

PTEN_0821

Table of Contents for the Digital Edition of PTEN_0821

Editor's Note
New Products
Diagnostic Tech
2021 Innovation Awards
Tool Briefing
Tool Reviews
Category Spotlight
Big-Time Boxes
PTEN_0821 - 1
PTEN_0821 - 2
PTEN_0821 - 3
PTEN_0821 - 4
PTEN_0821 - 5
PTEN_0821 - 6
PTEN_0821 - 7
PTEN_0821 - Editor's Note
PTEN_0821 - 9
PTEN_0821 - New Products
PTEN_0821 - RSC1
PTEN_0821 - RSC2
PTEN_0821 - 11
PTEN_0821 - 12
PTEN_0821 - 13
PTEN_0821 - 14
PTEN_0821 - 15
PTEN_0821 - Diagnostic Tech
PTEN_0821 - 17
PTEN_0821 - 18
PTEN_0821 - 19
PTEN_0821 - 2021 Innovation Awards
PTEN_0821 - 21
PTEN_0821 - 22
PTEN_0821 - 23
PTEN_0821 - 24
PTEN_0821 - 25
PTEN_0821 - 26
PTEN_0821 - 27
PTEN_0821 - 28
PTEN_0821 - 29
PTEN_0821 - 30
PTEN_0821 - 31
PTEN_0821 - 32
PTEN_0821 - 33
PTEN_0821 - Tool Briefing
PTEN_0821 - 35
PTEN_0821 - 36
PTEN_0821 - 37
PTEN_0821 - 38
PTEN_0821 - 39
PTEN_0821 - 40
PTEN_0821 - 41
PTEN_0821 - 42
PTEN_0821 - 43
PTEN_0821 - 44
PTEN_0821 - 45
PTEN_0821 - 46
PTEN_0821 - 47
PTEN_0821 - Tool Reviews
PTEN_0821 - 49
PTEN_0821 - 50
PTEN_0821 - 51
PTEN_0821 - Category Spotlight
PTEN_0821 - 53
PTEN_0821 - 54
PTEN_0821 - 55
PTEN_0821 - 56
PTEN_0821 - 57
PTEN_0821 - Big-Time Boxes
PTEN_0821 - 59
PTEN_0821 - 60
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