Brakes - Pedal Pulsation, Roughness, or Vibration
BULLETIN NO.: 95-T-15ISSUE 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:
^ Excessive brake rotor thickness variation
^ 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.
^ 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.
^ 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.
^ 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.
^ 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.
BRAKE SYSTEM INSPECTION
FRONT AND REAR DISC
1. Remove the front and rear wheels.
2. Visually inspect the brake rotors for signs of corrosion or wear. If brake rotor surfaces are severely blistered, corroded, or flaking, the brake rotors must be replaced.
IMPORTANT:
Check brake fluid level in master cylinder reservoir and remove fluid if necessary to prevent overflow when retracting caliper piston(s).
3. Manually check caliper movement; make sure calipers are not restricted. Calipers should move freely on the caliper pins.
4. Remove caliper pins and then remove calipers. Do not allow caliper to hang by the brake hose; suspend caliper with a metal wire attached to the strut spring. Inspect calipers and caliper hardware for the following:
a. Lock pin and guide pin for damage or corrosion. Replace if damaged or corroded. DO NOT ATTEMPT TO REMOVE CORROSION OR STRAIGHTEN LOCK PIN OR GUIDE PIN.
b. Lock pin and guide pin boots for deterioration. Replace any damaged parts.
c. Piston boot for deterioration following the "Front Caliper" and "Rear Caliper" disassembly and assembly procedures in the appropriate year service manual, and overhaul caliper if piston boot is damaged or malformed.
5. Check brake pads for freedom of movement in caliper brackets; pads should move freely in the caliper brackets.
6. Remove the front and rear brake pads.
7. Inspect the brake pads for corrosion on the brake pad's steel edge. Replace brake pads if they are severely corroded.
IMPORTANT:
Excessive corrosion on the edge of the shoe may restrict shoe movement in the caliper bracket. Shoe corrosion coupled with excessive brake rotor lateral runout can cause brake pulsation. The brake pads must move smoothly and freely in the caliper brackets.
8. Remove the brake pad spring clips, discard if installing new brake pad&
9. Measure brake rotor runout and thickness variation following the "Inspecting and Refinishing Brake Rotors" procedures in the service manual. Make sure brake rotors meet the minimum thickness specification of 15.8 mm (0.625 in.) for front brake rotors or 9.0 mm (0.350 in.) for rear brake rotors.
10. If brake rotor replacement is necessary based on the inspection or refinishing is necessary, remove caliper support bracket(s) and brake rotor(s).
11. Refinish brake rotors if necessary using the procedures in this bulletin.
12. Using a wire brush, clean the caliper support brackets in the area where the pad spring clips make contact with the brackets. Also, clean the caliper support brackets and knuckles where they make contact.
13. Install new or refinished brake rotor(s) if removed.
14. Install caliper support bracket(s) if removed.
15. Install new brake pad spring clips to brackets.
IMPORTANT:
Do not apply lubricant in this area. The lubricant may cause an excess accumulation of dirt and dust, resulting in higher shoe sliding friction.
16. Install new disc brake pads if they are extensively worn or severely corroded.
17. Position caliper(s) to bracket(s) and install guide and lock pins.
18. Manually check caliper movement; make sure calipers are not restricted. Calipers should move freely on the caliper pins.
19. Install road wheels. Make sure to torque wheel nuts, in a crisscross tightening sequence, with a hand-held torque wrench
Torque: 140 Nm (103 ft.lbs.)
REAR BRAKE DRUM AND HUB
BRAKE DRUM AND HUB RADIAL RUNOUT CHECK - ON-CAR
1. Remove road wheel.
2. Remove brake drum and install on hub backward; secure brake drum with two wheel nuts also installed backwards (flat side toward brake drum).
3. Fasten a dial indicator to the knuckle or strut - to - knuckle fastener.
4. Position dial indicator tip against brake drum shoe surface.
5. Rotate the brake drum to the lowest reading.
6. Zero the dial indicator.
7. Rotate the brake drum one complete revolution and observe total indicated runout (TIR). Maximum TIR (combined brake drum and hub): 0.28 mm (0.011 in.)
a. If the combined brake drum and hub radial runout does not exceed 0.28 mm (0.011 in.), proceed to step 8.
b. If the combined drum and hub radial runout exceeds 0.28 mm (0.011 in.), proceed to step 14.
8. Move dial indicator neck to allow removal of the brake drum. It is not necessary to remove dial indicator from the knuckle or strut-to-knuckle fastener.
9. Remove brake drum from hub and turn 180 degrees and again, install on hub backward. Secure brake drum with two wheel nuts also installed backwards (flat side toward brake drum).
10. Position dial indicator tip against brake drum shoe surface.
11. Rotate the brake drum to the lowest reading.
12. Zero the dial indicator.
13. Rotate the brake drum one complete revolution and observe total indicated runout (TIR).
Maximum TIR (combined brake drum and hub): 0.28 mm (0.011 in.)
a. If the combined brake drum and hub radial runout does not exceed 0.28 mm (0.011 in.), brake drum and hub are within specification and no repair is required. Refer to brake pulsation diagnosis in the appropriate year service manual.
b. If the combined brake drum and hub radial runout exceeds 0.28 mm (0.011 in.), proceed to step 14.
14. Remove brake drum and install on a brake lathe.
15. Fasten a dial indicator to the lathe.
16. Position dial indicator tip against brake drum shoe surface.
17. Rotate brake drum to the lowest reading.
18. Zero the dial indicator.
19. Rotate the brake drum one complete revolution and observe total indicated runout.
Maximum TIR (brake drum): 0.15 mm (0.006 in.)
If the brake drum radial runout exceeds 0.15 mm (0.006 in.), refinish brake drum as long as refinishing does not exceed brake drum maximum diameter of 200.6 mm (7.90 in.) after turning. If the brake drum exceeds maximum diameter, replace the brake drum.
20. Subtract total indicated runout (TIR) measurement obtained in step 19 (brake drum runout) from TIR measurement obtained in step 7 (combined brake drum and hub runout). The difference between these two readings represents hub runout.
Combined Drum and Hub Runout - Drum Runout = Total Hub Runout
Maximum TIR (hub): 0.13 mm (0.005 in.)
If the hub runout exceeds 0.13 mm (0.005 in.), replace the hub and bearing assembly.
21. Install road wheels. Make sure to torque wheel nuts, in a crisscross tightening sequence, with a hand-held torque wrench.
Torque: 140 Nm (103 ft.lbs.)
RECOMMENDED PROCEDURE FOR MACHINING BRAKE ROTORS
A brake rotor is a precision machined part. It must be properly machined to provide proper service.
1. All rust and corrosion must be removed from the mounting surfaces of the brake rotor. Use a wire brush or a wire wheel and a drill to remove all corrosion and scale from the mounting surfaces of the brake rotor.
2. Make sure the correct "bell clamps" are used to mount the brake rotor on the brake lathe. Some bell clamps may appear to fit flush inside the brake rotor, but actually they may be too large, forcing the brake rotor to "wobble" when it turns on the lathe. (Bell clamp outside diameter ("D") must be less than 139 mm (5.47 in.). If a brake rotor does not turn on a plane that is parallel to the brake lathe's cutting tip, lateral runout will be machined into the brake rotor
3. Both surfaces of the inside bell clamp must be parallel or the brake rotor will not turn on a parallel plane with the cutting tip. If a bell clamp is dropped or damaged, contact the brake lathe's manufacturer to obtain a new bell clamp.
4. Use the largest possible "spacers" to hold the bell clamps on the lathe's spindle. This - will insure that the most weight possible is on the spindle, helping the brake rotor to turn on a plane parallel to the brake lathe's cutting tip.
5. Before machining, use a magnetic dial indicator to make sure that the brake rotor turns squarely on the brake lathe. Attach dial indicator on lathe and check brake rotor runout. Mark highest point of lateral runout on the brake rotor. Loosen attachment hardware and rotate brake rotor 180 degrees (1/2 turn) while holding the inside bell clamp in its original position. Tighten attachment hardware and recheck brake rotor runout. Any runout must follow the brake rotor. That is, the already marked high spot on the brake rotor must remain the high spot. If not, some problem exists in the attachment of the brake rotor on the lathe, such as bent bell clamps, incorrect bell clamps, or untrue mounting surfaces.
6. After turning the brake rotor, visually check the machined brake rotor's surface finish. Any deterioration in the machined surface finish quality of the brake rotor usually indicates worn cutting tips. Always use the cutting tips recommended by the brake lathe's manufacturer.
7. A secondary finishing operation improves brake rotor surface finish. Saturn recommends using silicon carbide 150 grit emery paper mounted on a sanding block. Using moderate pressure, hold the paper against the brake rotor for 90 seconds per side as it turns in the lathe.
8. Thoroughly clean machined brake rotors with a spray solvent such as Saturn Choke Cleaner (P/N 21007127) or Saturn Brake and Choke Cleaner (P/N 21007432) or equivalent.
INFORMATION ON PERFORMING BRAKE SERVICE
Several important factors are frequently overlooked when performing brake service. The following list must be considered and followed when appropriate:
1. Proper machining of brake rotors is not a simple operation. Make sure the brake lathe is well maintained. Keep it clean at all times. Handle attachment hardware with care. Damaged hardware will not machine brake drums or brake rotors accurately. Inspect the surface finish of machined brake rotors and brake drums to make sure the cutting tips are in good condition. Make sure the cutting tips remain in good condition. Use a dial indicator to make sure brake rotors turn squarely on the brake lathe. (Refer to step 5 under the "Recommended Procedure for Machining Brake Rotors" in this bulletin.)
2. Keep all installed brake parts as clean as possible. Make sure to clean machined brake rotors and brake drums with a spray solvent (Saturn Choke Cleaner P/N 21007127 or Saturn Brake and Choke Cleaner PIN 21007432 or equivalent). Always wipe off machined brake rotor surfaces with a lint free shop towel after cleaning.
3. Thickness variation of brake rotors due to wear is a major cause of brake pulsation. Using a micrometer, check for excessive thickness variation whenever a customer comments on brake pulsation.
4. Lateral brake rotor runout and restricted pads together are the leading cause of uneven brake rotor wear. Therefore, this combination leads directly to brake pulsation.
IMPORTANT:
Make sure calipers slide freely on their pins; make sure brake pads move freely in their brackets.
5. Uniform wheel nut torque is very important. Uneven torque can distort brake rotors, causing excessive lateral brake rotor runout. A hand-held torque wrench must be used to secure wheel nuts using a crisscross tightening pattern, even when a torque stick and an air-powered impact gun are used.
Torque: 140 Nm (103 ft.lbs.)
6. After brake rotors/brake drums and brake pads/shoes have been replaced, proper break-in promotes longer life and quieter, smoother brake operation. To obtain proper break-in, follow this procedure:
a. From 48-64 km/h (30-40 mph), apply brakes gently until vehicle slows nearly to a stop. Accelerate vehicle back to 48-64 km/h (30-40 mph) and drive long enough for brakes to cool (30-40 seconds). Repeat this procedure five times, each time allowing sufficient time between stops for brakes to cool.
b. Complete the break-in procedure by accelerating the vehicle to 88 km/h (55 mph), then gently slowing the vehicle from 88-32 km/h (55-20 mph) four times. Allow 30-40 seconds between intervals for brakes to cool. This break-in procedure will reduce brake noise and increase brake life and performance.
PARTS REQUIREMENTS:
21011105 Rotor-Frt Disc Brk
21012526 Pad Kit-Frt Disc Brake
21010591 Spring Kit-Frt Disc Pad Rtn
21011106 Rotor-RR Disc Brk
21010593 Pad Kit-RR Disc Brk
21010562 Spring Kit-RR Disc Pad Rtn
21010543 Boot Kit-Frt/RR Caliper Mtg Pin
21010545 Pin Kit-Frt/RR Caliper Mtg
21011906 Drum-Brk
CLAIM INFORMATION:
To receive credit for this repair during the warranty coverage period, submit a claim through the Saturn Dealer System using the appropriate electronic Saturn Labor Time Guide for the correct Labor Operation Code and Time.