Chevrolet T-Series Owner's Manual page 61

The exhaust brake button is located in the
instrument panel.
Push the bottom of the button to turn the exhaust
brake on. When you push the top of the switch,
the exhaust brake will turn off.
There is an indicator light on the instrument panel
similar to the symbol on the switch, that will
come on when the exhaust brake is active. See
Exhaust Brake Indicator Light on page 114
for more information.
When using the exhaust brake, the proper gear
range selection is important. The exhaust
brake will be most effective if the gear range
selected is the lowest possible range that does not
allow the engine rpm to exceed 2500 rpm.
If you have an automatic transmission and press
this button, the transmission will downshift to
a factory default setting of fourth gear. To change
the default setting, or for more information on
factory default settings, contact your dealer
for assistance.
The accelerator and clutch pedals, on a manual
transmission, must be released in order for
the exhaust brake to engage.
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