SW L4-1.9L DOHC VIN 7 (1993)
Brake Drum: All Technical Service Bulletins
Brakes - Pedal Pulsation, Roughness, or Vibration
BULLETIN NO.: 95-T-15
ISSUE DATE: March, 1995
GROUP/SEQ. NO.: Chassis-04
CORPORATION NO.: 585003
SUBJECT:
Brake Pedal Pulsation and/or Vehicle Vibration During Brake Apply (Diagnosis/Service Procedures)
MODELS AFFECTED:
1991 - 1995 Saturns
CONDITION:
Some customers may comment on brake pedal pulsation, roughness, and/or vehicle vibration during brake pedal apply.
CAUSES:
The most common causes for the above conditions are as follows:
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Excessive brake rotor thickness variation
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Excessive brake drum radial runout or ovality
IMPORTANT:
For 1993 vehicles, this information will be in the second edition, "1995 Brakes Service Manual."
There are two primary causes for excessive brake rotor thickness variation. The first is corrosion of the brake rotor or lining friction surfaces. Corrosion
build-up causes high spots on the brake rotor surface which can lead directly to brake pulsation.
The second cause is a combination of two conditions: excessive brake rotor lateral runout and a restricted brake pad or caliper. Both conditions
(excessive brake rotor lateral runout and restricted brake pad or caliper) must occur for thickness variation and pulsation to result. One or the other by
itself will not cause brake pulsation.
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Excessive brake rotor lateral runout can result from several conditions. The most common cause is incorrect or uneven wheel nut torque. (Refer the
Technical Information Bulletin 94-T-40 for important information concerning wheel nut torque procedures and tools.) Excessive brake rotor lateral
runout may also be caused by any of the following: poor brake rotor refinishing equipment and/or procedure, excessive hub and bearing assembly
lateral runout, or wheel, brake rotor or surfaces that are corroded, damaged or dirty.
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The most common cause for a restricted brake pad is excessive corrosion of the brake pad shoe, spring clip and/or support bracket at the
pad-clip-bracket interface. An incorrect, damaged, poorly positioned, or missing brake pad spring clip may also cause restricted brake pad
movement.
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The most common cause for restricted brake caliper are conditions related to the slide pins (lock and guide pins) and corresponding support bracket
bore. Some of the slide pin conditions which can cause restricted caliper movement are: bent or damaged slide pins, corroded slide pins or slide pin
bores, or incorrect or insufficient lubricant at caliper slide pins or slide pin bores. Generally, corrosion of the caliper slide pins or slide pin bores is a
result of damaged or mis-positioned slide pin boots.
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Another potential cause for restricted brake pad/caliper movement or brake drag is an incorrectly adjusted stop lamp switch. Refer to Technical
Information Bulletin 93-T-13 for important information concerning slight brake drag.
Excessive brake drum radial runout or ovality may be caused by poor brake drum refinishing equipment and/or procedure, or excessive hub and bearing
assembly radial runout.
CORRECTION
Perform a brake system inspection according to the procedure in this bulletin on any vehicle exhibiting brake pulsation, brake vibration, or brake
roughness. Corrections should be made according to the procedures in this bulletin.
PROCEDURES
IMPORTANT:
Refer to "1991-1994 Brakes Service Manual" or first or second edition "1995 Brakes Service Manual" for further service procedures and
specifications as required.
