Beretta V6-173 2.8L (1989)
Brake Rotor/Disc: All Technical Service Bulletins
Brakes - Change In Brake Feel After Rotor Refinishing
Number: 91-133-5
5
Section: 5
Date: December 1990
Corporate Bulletin No.: 075003R
Subject:
CHANGE IN BRAKE EFFECTIVENESS AFTER DISC BRAKE ROTOR REFINISHING/PAD REPLACEMENT
Model and Year:
ALL PASSENGER CARS ALL LIGHT DUTY TRUCKS
TO: ALL CHEVROLET DEALERS
THIS BULLETIN CANCELS AND SUPERSEDES DEALER SERVICE BULLETIN NO. 90-316-5, DATED AUGUST 1990. INFORMATION HAS
BEEN ADDED REGARDING HUB AND ROTOR CLEANING, PROPER TORQUING TECHNIQUE, REVISED MACHINING TABLE, CHANGE
SPECIFICATION FOR MAXIMUM SCORINGING DEPTH. THE 1991 MODEL YEAR WAS ALSO ADDED. ALL COPIES OF 90-316-5 SHOULD
BE DISCARDED.
Some comments have been received about a change in preceived braking effectiveness which occurs after rotors have been refinished and/or disc brake
pads have been replaced. New lining materials have been formulated for increased lining life and to reduce brake squeal. Also, Federal regulations
currently prohibit the use of asbestos in Original Equipment Manufactured (O.E.M.) front disc brake linings, and will totally ban asbestos from all
O.E.M. brake linings in the near future. Due to these changes, initial rotor surface finish is more critical than in the past, and is required for good brake
performance.
Following are some recommended actions/procedures to assure proper performance of the brake systems on all vehicles after rotor and/or pad service
has been performed:
1
. When performing routine brake maintenance such as replacing worn disc brake pads or shoes, DO NOT refinish disc brake rotors or drums
unless:
A.
There is a brake pulsation condition present, and this pulsation is found to be caused by the brake rotors or drums, or
B.
The rotors and/or drums are excessively scored. Surface scoring that does not exceed 1.2 MM (0.050 in.) on rotors or drums should not
affect brake operation.
Before removing rotors from the hub assembly, mark the rotor and on wheel stud so that the rotor may be re-installed in the same position.
If rotors are removed, it is very important that rust and scale be removed from the rotor and hub mating surfaces. Failure to do so may introduce
excessive lateral runout when the rotor is mounted on the brake lathe, or when the rotor is re-installed to the hub.
2.
When refinishing disc brake rotors, it is important that the brake lathe be in good operating condition and that all tools or bits are sharp.
Recommended vibration dampeners and/or adaptors should be used and should be clean and free of nicks (remember, 1988-91 W models
require the use of an adaptor, J37160, because of the two-piece design). The following table shows the recommended procedure for rotor
machining:
ROUGH CUT
FINISH CUT
Spindle Speed
150 RPM
150 RPM
Depth of Cut (per side)
0.127 mm (0.005")
0.051 mm (0.002")
Tool Cross Feed per Rev
0.152 mm - 0.254 mm
0.051 mm (0.002")Max
(0.006" - 0.010")
Vibration Damper
Yes
Yes
Sand Rotors-Final Finish
No
Yes
It is important that a rough and a finish cut be made. All brake lathes use a single-point cutting tool which is not capable of giving the necessary
surface finish. A SECONDARY FINISHING OPERATION MUST BE PERFORMED TO OBTAIN THE NECESSARY SURFACE FINISH.
