GMC 2007 Envoy - Manual (Page 369)

If you will be pulling a trailer that, when loaded,
will weigh more than 5,000 lbs (2 270 kg) be sure
to use a properly mounted weight-distributing
hitch and sway control of the proper size.
This equipment is very important for proper vehicle
loading and good handling when driving. Always
use a sway control if the trailer will weigh
more than these limits. You can ask a hitch dealer
about sway controls.
Safety Chains
You should always attach chains between your
vehicle and your trailer. Cross the safety
chains under the tongue of the trailer to help
prevent the tongue from contacting the road if it
becomes separated from the hitch.
Instructions about safety chains may be provided
by the hitch manufacturer or by the trailer
manufacturer. Follow the manufacturer’s
recommendation for attaching safety chains and
do not attach them to the bumper. Always leave
just enough slack so you can turn with your rig.
Never allow safety chains to drag on the ground.
Trailer Brakes
If your trailer weighs more than 1,500 lbs. (680 kg)
loaded, then it needs its own brakes — and
they must be adequate. Be sure to read and follow
the instructions for the trailer brakes so you’ll be
able to install, adjust and maintain them properly.
Your trailer’s brake system can tap into the
vehicle’s hydraulic brake system only if:
• The trailer parts can withstand 3,000 psi
(20 650 kPa) of pressure.
• The trailer’s brake system will use less than
0.02 cubic inch (0.3 cc) of fluid from your
vehicle’s master cylinder. Otherwise,
both braking systems won’t work well.
You could even lose your brakes.
If everything checks out this far, then make the
brake fluid tap at the port on the master cylinder
that sends fluid to the rear brakes. But don’t
use copper tubing for this. If you do, it will bend
and finally break off. Use steel brake tubing.
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