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Idiomas disponibles
Idiomas disponibles
Testing Anti-Lock Brake Systems
Anti-lock Brake Systems (ABS) are divided into two categories: integral systems and non-integral
systems. An integral ABS system is a self-contained unit that houses the needed electrical and
mechanical components that provide the control and power assist to the brakes. An integral system
does not use the conventional master cylinder and vacuum booster, but replaces it with a unified
hydraulic unit. Before doing any testing or servicing on an integral ABS system, the unit must be
depressurized for safety as me unit is a high pressure system.
Conversely, a non-integral ABS system is a low-pressure system that utilizes the existing master
cylinder and vacuum booster. It uses additional specific electronic devices that are built into the
existing conventional brake system to perform the anti-lock functions.
Testing Integral ABS Systems
Pressure checking integral ABS master cylinders is done to determine pump and accumulator
pressure. On all ABS integral master cylinders the "boost" for the power assist is obtained from the
pump and the accumulator. Specific OE instructions are given in the ABS and OE manuals for these
pressure checks.
Master cylinder outlet port pressure and the amount of pedal effort required to obtain the pressure will
vary greatly if the accumulator and pump are not in proper working order. Also, on some integral ABS
systems the rear brake pressure cannot be checked except at the wheel because the rear brake
pressure is supplied only from the pressure stored in the accumulator. For these reasons, integral
ABS master cylinders should only be tested according to OE procedures. These procedures do not
cover checking outlet pressure from the ports of me master cylinder. Checking outlet port pressure
without following the prescribed OE diagnostic procedures could easily lead you to an incorrect
diagnosis of a problem. Also, because of the high pressure of the fluid stored in the accumulator,
safety is a concern. If you want to know the outlet pressure of the master cylinder, check it at the
wheels after following the OE procedure for verifying correct accumulator and pump pressure.
Service Safety Warning: Before performing any pressure checks at the master cylinder the
accumulator must be discharged. To discharge the accumulator, turn the ignition key to the off
position. Next pump me brake pedal 25-35 times until it becomes rock hard, then pump the pedal an
additional 5 times. Only after the accumulator is discharged can the adapter and the pressure gauge
be safely installed or removed.
DELCO III System Integral ABS master cylinder pressure checks
The following checks will determine if the accumulator has lost its nitrogen charge on me top side of
the bladder, determine total system pressure, give an indication of pump capacity and establish the
operation of me high and low pressure switches on DELCO HI systems.
(Applications: various Buick Regal, Oldsmobile Cutiess Supreme, Jeep Cherokee & Pontiac Grand
Prix, 1989-1997)
Procedure (1-3/7)
1. Check the bottom screw thread area of the accumulator to be sure that the sealing 0-ring did not
stick to the master cylinder. Also check the O-ring for nicks, cuts, or tears. If the 0-ring is not
perfect it must be replaced.
2. Loosen the accumulator from the integral master cylinder. Alien head or torx sockets are used
with a 3/8" rachet to loosen the accumulator. The socket is placed into the torx or alien hex hole
on the top of the accumulator.
3. Depressurize the accumulator. With me key off, pump the brake pedal 20-30 times until it
becomes rock hard. Pump the pedal an additional 5 times.
BGS technic KG
Bandwirkerstr. 3
D-42929 Wermelskirchen
Tel.: 02196 720480
Fax.: 02196 7204820
www.bgstechnic.com
© BGS technic KG, Copying and further use not allowed
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