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Uneven Pad Wear or Brake Pull to One Side
If you have uneven pad wear side to side or a brake pull, hook up the pressure gauges to both front
calipers. Check the brake pressure at both gauges while an assistant depresses the brake pedal. If
the brake pressures are the same at both wheels, there may be a mechanical condition such causing
the problem.
Testing Rear Load Sensing Valves
The following generalized instructions will give you guidelines for the proper use of brake pressure
gauges for setting rear ride height proportioning valves.
A detailed shop manual must be obtained and the procedures followed to set the ride of height
proportioning valve for each specific vehicle. These generalized instruction do however give an
overview and basic insight into this necessary procedure.
Instructions basically consist of specifying that the vehicle is to be on a flat surface with a specific
load, and a driver in the vehicle.
Instructions then call for pressure gauges to be connected to Ac front and rear wheels.
Depending upon the specific design of the valve, whether it is a rear brake proportioning only or a
dual sensing or bypassing type of valve, perform various pressure checks according to OE
procedures.
Certain vehicles use rear brake pressure control valves. These include the Ford Motor Company's
Taurus and Sable sedans, Chrysler's mini-vans and imported sport utility and passenger vehicles
such as the Nissan Quest, Isuzu pick-up, Suzuki Sidekick, Toyota pick-up trucks and many others
OE repair manuals for these vehicles call for various specific and detailed procedures to be followed
for the adjustments of these valves when they are adjustable, and give the tests to determine
serviceability and operation of this valve when they are used but are not adjustable.
On the valves that are rear pressure sensing only, me rear brake pressure control depends upon the
vehicle height. On these vehicles, generally the instruction state to depress the brake pedal slowly
establish a certain front pressure and check the rear pressure. If you wish to determine if the
switching of the valve is correct or not, you could perform a simple check of the valve, and then raise
the rear of the vehicle and check pressure and then load the rear of the vehicle and check pressure.
The relationship of the rare brake pressure to the front pressure should be noticeably different under
the two different conditions.
On vehicles which use the dual sensing or bypassing rear brake proportioning valve, instructions
typically are as follows:
1. Apply force to the brake pedal in a slow and controlled manner until you have a front brake
pressure as stated in me vehicle's OE manual. This pressure will most likely be in the 780-1100
PSI range. At that pressure you should have a rear brake pressure which is approximately 55-75
of the front.
2. Premature or very rapid front disc brake pad wear can be a result of a maladjusted rear ride
height proportioning valve. High pedal effort problems, rear wheel lock-up under slippery road
driving or other weather conditions and aggressive side pull from rear brakes are all indications of
possible rear load sensing valve maladjustment or malfunctions. Without pressure gauges, such
as the ABS & Brake Pressure Test Kit, the cause of these conditions is virtually impossible to
identify from a hydraulic pressure standpoint.
3. Continue to increase pressure on the brake pedal in a slow controlled manner and watch for the
pressure on both the front and rear to rise. When the front hydraulic pressure reaches
approximately 1300-1700 psi, the rear brake pressure should have increased to approximately
80- 85 of the front. The pressures specified above are the result of a consolidation of information
presented in the OE manuals for several different vehicles, in all cases an OE or aftermarket
manual should be consulted to determine the specific pressures that should exist on the vehicle
being tested.
4. The ABS & Brake Pressure gauge set, used with me correct included adapters, will enable you to
determine the operation of the various rear brake pressure control valves. This can assist you in
diagnosing rapid front pad wear, rear wheel lock-up problems and other brake conditions that
would not be able to be determined without the use of effective pressure gauges.
BGS technic KG
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D-42929 Wermelskirchen
Tel.: 02196 720480
Fax.: 02196 7204820
mail@bgs-technic.de
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