PS Magazine - TB 43-PS-569
PS, The Preventative Maintenance Monthly
ISSUE 569
APRIL 2000
PS 569
8
APR 00
Make sure hand brake holds
rivers,
what do master
cylinders, air tanks,
emergency brakes
and chock blocks
have in common?
If each is used
properly and taken
care of, they’ll stop
your trailer or
semitrailer.
..and
keep it stopped until
you’re ready to roll again.
Master Cylinders
Many small trailers have hydraulic
brakes. That means they’ve got a mas-
ter cylinder that needs regular service.
Some are easy to find, like the one
on M149A2 water trailers. It’s right
behind the lunette.
Others are not so easy. On other
1
1
/
2
-ton trailers, the cylinder is under
the chassis, next to the curbside wheel.
Your operator’s manual will pinpoint
the location. Then you need to make
sure there’s enough fluid in the master
cylinder to make the brakes work.
Trailers, Semitrailers . . .
While your trailer is still hooked up,
set the brake and try to pull the trailer
forward with the truck. If the brakes
are working, the tires won’t roll.
On the other hand, forget using trailer
emergency brakes during cold weather.
The cable and handle can freeze and
break when you try to use them. Then
you can’t release the brakes. During
cold weather, always use two chock
blocks instead of emergency brakes.
If your trailer’s not hooked to a truck,
and it’s on level ground, use chocks in
front of one wheel and behind the
wheel on the other side.
Put both chocks on the downhill
side when parked on a slope.
Before moving out, stow the
blocks in a safe place, like in
their brackets, in a tool box
or in some other handy place.
Before You Go
When you’re ready to go, a quick
check to make sure your brakes are
hooked up right is to roll and stop the
vehicle. If it stops, then rolls again once
the brakes are released, the brakes are
right.
If the trailer rolls, stops, and won’t
roll again when the brakes are released,
the brakes are locked up, which means
only one thing—the air lines are con-
nected backward. So, change ’em.
Emergency!
It does no good to set your emer-
gency brake if it doesn’t work, so be
sure it does.
Air Tanks
Other trailers, especially semitrail-
ers, use air brakes. That means there
are air tanks to be drained each day
after operation. Draining gets rid of
water that would freeze brake lines in
cold weather or corrode them in any
weather.
After you drain the air tanks, close
the drain cocks. Leaving them open
lets condensation back inside the tanks
when temperatures go from hot to cool.
An open drain cock also lets any-
thing small enough to crawl inside
(like bugs) or to blow inside (like dirt).
PS 569
9
APR 00
before
you get your
trailer rolling,
make sure you can
stop
and
stay
stopped
.
she's
chock
full
of
pm
.
yeah,
she's got all
the
braking
news
.
Enough fluid in master cylinder?
Open drains, then close ’em
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