RayTek Rayst25 Autopro User Manual page 14

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Brakes (Cont.)
To obtain an accurate temperature reading, test
drive vehicle in a low-traffic area, preferably on a
straight, level section of roadway. Operate
vehicle to 50 KM/H (30 MPH) and bring to a
complete stop 5 times. Stop vehicle, place in
Park (auto trans) or neutral (manual trans) and
set parking brake. Using the IR thermometer,
measure temperature of front and rear brakes.
See Figs. 2 & 3.
Fig. 2: Measuring Disc Brake Temperatures
If temperature differential between front and rear
brakes is greater than 30°C (50°F), rear brakes
may not be working effectively. Check the
following:
Front brake adjustment too tight (drum
brakes - front).
Rear brake adjustment too loose (drum
brakes - rear).
Emergency brake adjustment.
Combination valve malfunction.
Master cylinder malfunction (check for loss
of brake fluid without a visible fluid leak).
Leaking calipers or wheel cylinders.
Master cylinder overfilled.
Brake line or hose restriction.
If temperature differential is less than 30°C
(50°F), or rear brake temperature is hotter than
front brakes, front brakes may not be working
effectively. Check the following:
Front brake adjustment too loose (drum
brakes - front).
10
Rear brake adjustment too tight (drum
brakes - rear).
Emergency brake adjustment too tight.
Combination valve malfunction.
Master cylinder malfunction.
Leaking calipers or wheel cylinders.
Brake line or hose restriction.
Some vehicles also have a load-sensing valve
near the rear brakes. Check this valve for proper
operation where applicable.
Fig. 3: Measuring Drum Brake Temperatures
Diagonal Split Brake Systems
Diagonal split brake systems differ from front/rear
split systems in that each circuit of the master
cylinder operates one front brake and the
diagonally opposite rear brake. See Fig. 4.
As in front/rear split brake systems; diagonal split
brake systems front brakes will normally have
higher temperatures than rear brakes when
working properly. Normal temperature differential
between front and rear brakes is 30°C (50°F).
Diagonal split brake system symptoms are often
related with a brake pull. This is when the vehicle
pulls to left or right when the brakes are applied.
This procedure trouble shoots operation of the
diagonal split brake system and applies to
vehicles with disc/disc or disc/drum brake
configuration.
To obtain an accurate temperature reading, test
drive vehicle in a low-traffic area, preferably on a
straight, level section of roadway. Operate
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