PS Magazine - TB 43-PS-570
PS, The Preventative Maintenance Monthly
ISSUE 570
MAY 2000
Brakes . . .
Vent
hole on
back of
coupling
irt and moisture have a clear shot at your vehicle’s air line connectors and
receptacles if you don’t use dummy couplings. Grit can plug up a valve or
moisture can rust it shut, leaving you brakeless.
When you unhook air lines, put the dummy couplings on the truck’s half
couplings. Hook the trailer’s air lines to
the dummy connectors on the trailer
frame.
Make sure you use a vented dummy
coupling, NSN 2530-00-740-9445, on
the front service brake coupling of
vehicles with air-hydraulic brake
systems, such as M39-series and
M809-series 5-ton trucks.
Without a vent, back pressure
builds up in the air-hydraulic cylinder when you step on the brake pedal. The
cylinder can’t release air, so the brakes lock up.
If you have a vented coupling, but the brakes still lock up, make sure the vent
is open. Blow into it. You should feel air coming through. If not, take it off and
clean it in soapy water. Rinse and let it dry completely.
Blow into the vent again. If you still can’t feel air coming through it, tell your
mechanic. He’ll replace the bad coupling with a good one.
Use vented dummy coupling
PS 570
13
MAY 00
yikes!
i'm a
goner
!
heh,
heh!
i've
got a
clear
shot
!
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