GMC 2003 C4C042, Owner'S Manual, Page: 111 / 386

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Overdrive Defeat (If Equipped)
If your vehicle has this feature, you can select not to
shift up to fifth gear. This is useful when towing or
under a heavy load.
The overdrive defeat switch
is located in the instrument
panel to the right of the
steering column.
Press the switch to limit the transmission to fourth gear.
This will allow for better fuel economy and fewer
downshifts while pulling a tractor or trailer or under a
heavy load. The indicator light in the switch will come
on whenever overdrive defeat is active.
Manual Transmission Operation
Using the Clutch
When you’re starting to move the vehicle, it’s important
to begin with the engine speed at idle. Then start to
engage the clutch and listen for an engine speed drop
of about 100 rpm. At this point, the clutch is engaging,
so you should increase the engine speed and fully
engage the clutch. It’s important not to increase the
engine speed sooner or before the clutch begins it’s
engagement. If you do, you can cause damage to
your vehicle.
Double-Clutching
You must use the double
-
clutching method when you
shift an unsynchronized gear set. Disengage the clutch,
shift to neutral and engage the clutch. When upshifting,
slow the engine until the engine rpm and road speed
match. When downshifting, accelerate the engine until
the engine rpm and road speed match. Then quickly
disengage the clutch and move the shift lever to the next
gear position and engage the clutch.