GMC 2003 C4C042 Owner's Manual page 236

Here are specific towing instructions:
Towing Your Vehicle From the Front
(Front Wheels Off the Ground)
Before Towing
Block the rear wheels of the disabled vehicle. On
vehicles with air brakes, release the emergency brake
system by compressing the brake chamber springs
as outlined in this section. (This is to prevent the
possibility of the emergency brake being applied
during towing.)
On vehicles with hydraulic brakes, release the parking
brake fully by moving the lever to the fully
position.
Disconnect the propshaft at the rear axle (forward axle
on tandem axle models). Secure the propshaft to the
frame or crossmember.
Towing the Vehicle with the Front Bumper Removed
1. Remove the front bumper.
2. Connect and lock the lift chains to the front axle,
outside of the spring anchor plates as shown.
-
released
A. Spring Anchor Plate
B. Lift Chain
C. Front Axle
3. Place a 6" x 6" x 5' hardwood beam underneath and
slightly behind the front spring shackle brackets.
4. Connect the lift chains to the tow bar and raise the
tow bar until lift chain slack has been taken up and
the hardwood beam is fully seated against the spring
shackle brackets as shown.
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