Chevrolet Cobalt Service & Repair Manual: General Service
| Two basic types of power assist
mechanisms are used: vacuum assist diaphragm assemblies, which use engine
vacuum or in some cases vacuum pressure developed by an external vacuum
pump. The second type is a hydraulic pressure assist mechanism, which use
pressure developed by an external pump (usually the power steering pump).
Both systems act to increase the force exerted on the master cylinder piston
by the operator. This in turn increases the hydraulic pressure delivered
to the wheel cylinders while decreasing driver effort required to obtain
acceptable stopping performance. |
| Vacuum assist units are similar
in operation and get their energy by opposing engine vacuum to atmospheric
pressure. A piston and cylinder, flexible diaphragm (bellows) utilize this
energy to provide brake assistance. The fundamental difference between these
types of vacuum assist systems lies simply in how the diaphragm within the
power unit is suspended when the brakes are not applied. |
| In order to properly diagnose
vacuum assist system faults it is important to know whether the diaphragm
within a power unit is air suspended or vacuum suspended. Air-suspended
units are under atmospheric pressure until the brakes are applied. Engine
vacuum is then admitted, causing the piston or diaphragm to move (or the
bellows to collapse). Vacuum-suspended types are balanced with engine vacuum
until the brake pedal is depressed, allowing atmospheric pressure to unbalance
the unit and apply force to the brake system. |
| Regardless of whether the brakes
are vacuum or hydraulically assisted, certain general service procedures
apply. Only specified, clean brake fluid should be used in brake systems.
On hydro-boost systems, use of the specified hydraulic fluid in the boost
circuit is essential to proper system operation. Care must be taken not
to mix the fluids of the two separate operating circuits. |
AC-Delco Tandem Diaphragm Type
This unit utilizes a vacuum power
chamber, consisting of a front and rear shell, housing divider, front and
rear diaphragm, plate assemblies, hydraulic p ...
1.
After disassembling power brake unit,
soak metal components in solvent.
2.
Use only alcohol on components containing
rubber. Aft ...
See also:
Chevrolet Cobalt Owners Manual. Passing
Passing another vehicle on a two-lane road can be
dangerous. To reduce the risk of danger while passing:
- Look down the road, to the sides, and to
crossroads for situations that might affect a
successful pass. If in doubt, wait.
- Watch for traffic signs, pavement markings, and
lines that cou ...
Description
Precautions