POWER STEERING GEAR HISS (REPL. POWER STG. ASSY.)

REVISION 01/20/94

THIS BULLETIN IS BEING REVISED TO ADD INFORMATION ON PITMAN SHAFT OVER-CENTER PRELOAD ADJUSTMENT. PREVIOUS DIVISIONAL PUBLICATION NUMBER WAS: CHEVROLET - 93-128-3B, DATED MARCH 1993. ---------------------------------------------------------------------- SUBJECT: POWER STEERING GEAR HISS (REPLACE POWER STEERING VALVE ASSEMBLY)

MODELS: 1985-93 CHEVROLET AND GMC M-VANS 1990-93 CHEVROLET AND GMC L-VANS

CONDITION:

SOME OWNERS MAY COMMENT THAT A HISSING NOISE CAN BE HEARD EMANATING FROM THE POWER STEERING GEAR DURING PARKING LOT TYPE MANEUVERS.

CAUSE:

THE HISS CONDITION IS CAUSED BY THE CAVITATION (HIGH PRESSURE/VELOCITY) OF THE POWER STEERING FLUID AS IT PASSES THROUGH THE CLOSING EDGES OF THE SPOOL VALVE CONTAINED WITHIN THE POWER STEERING GEAR. THIS CONDITION IS INHERENT TO THE GEAR DESIGN AND POSES NO THREAT TO STEERING SYSTEM INTEGRITY, PERFORMANCE OR DURABILITY.

CORRECTION:

TO MINIMIZE THIS CONDITION, A NEWLY DESIGNED SPOOL VALVE (PART NUMBER 26036745) HAS BEEN RELEASED FOR SERVICE ONLY. THE NEW SPOOL VALVE WILL REDUCE THE AMOUNT OF CAVITATION (HISS) OF THE FLUID.

SERVICE PROCEDURE:

REMOVE:

1. POWER STEERING GEAR FROM THE VEHICLE (FIGURE 1).

- REFER TO SECTION 3B1 OF THE APPROPRIATE M/L VAN SERVICE MANUAL FOR COMPLETE REMOVAL INSTRUCTIONS OF THE POWER STEERING GEAR FROM THE VEHICLE.

2. ADJUSTER PLUG LOCKNUT (245) FROM THE STEERING GEAR (FIGURE 2).

NOTE: CARE SHOULD BE TAKEN NOT TO RAISE A BURR ON THE BACK OF THE LOCK NUT (245) DURING REMOVAL. A BURR MAY CAUSE A PROBLEM WITH PERCEIVED VALVE EFFORT AFTER REASSEMBLY, IF IT IS SEVERE ENOUGH TO COCK THE VALVE IN THE BORE.

3. ADJUSTER PLUG VALVE ASSEMBLY (240) USING J7624 (FIGURE 3).

4. REMOVE THE STEERING VALVE (250) AND STUB SHAFT ASSEMBLY FROM THE POWER STEERING GEAR HOUSING (FIGURE 1).

IMPORTANT

REMOVAL OF THE STEERING VALVE (FIGURE 4, ITEM 250) AND STUB SHAFT SHOULD BE DONE BY PULLING STRAIGHT OUT FROM THE POWER STEERING GEAR HOUSING BORE. DO NOT REMOVE THE WORM SHAFT (248) AND THRUST GEARING ASSEMBLY (246, 247) WHEN REMOVING THE STEERING VALVE ASSEMBLY. REMOVING THE WORM SHAFT WILL RESULT IN ONE OR MORE BALLS DROPPING OUT OF THE STEERING WORM CIRCUIT. LOSS OF ANY BALLS IN THE CIRCUIT WILL REQUIRE A COMPLETE REBUILDING OF THE STEERING RACK AND WORM ASSEMBLY.

INSTALL:

IMPORTANT:

THE VALVE BODY ASSEMBLY, RINGS AND ALL SEALS SHOULD BE LUBRICATED WITH POWER STEERING FLUID BEFORE ASSEMBLY.

1. INSTALL NEW STEERING VALVE ASSEMBLY P/N 26036745 (250) (FIGURE 1).

NOTE: PIN (A) ON THE WORM GEAR (248) LINES UP WITH SLOT (B) IN THE STEERING VALVE ASSEMBLY (250) (FIGURE 4). WHEN INSTALLING ADJUSTER PLUG (240), CARE SHOULD BE TAKEN NOT TO CUT THE SEALS.

2. ADJUSTER PLUG ASSEMBLY (240) USING J7624 (FIGURE 3).

ADJUST (FIGURE 5, STEPS A THROUGH E)

. BEARING PRELOAD

A. BEFORE ADJUSTING BEARING PRELOAD, ROTATE THE STUB SHAFT BACK AND FORTH TO DRAIN ALL OIL FROM THE GEAR (FIGURE 5, A).

B. USE TOOL J7624. TURN THE ADJUSTER PLUG (240) TO THE LEFT UNTIL THE PLUG ASSEMBLY IS FIRMLY BOTTOMED TO 30 N.M (22 LBS. FT.) (FIGURE 5, B).

C. MARK THE HOUSING IN LINE WITH ONE OF THE HOLES IN THE ADJUSTER PLUG (FIGURE 5, C).

D. MEASURE BACK (TO THE LEFT) 13 MM (1/2 INCH) AND REMARK THE HOUSING (FIGURE 5, C).

E. ROTATE THE ADJUSTER TO THE LEFT UNTIL THE HOLE IN THE ADJUSTER IS IN LINE WITH THE SECOND MARK (FIGURE 5, D).

F. INSTALL ADJUSTER PLUG LOCKNUT (245) AND TIGHTEN SECURELY BY LIGHTLY TAPPING A BRASS PUNCH INTO ONE OF THE NOTCHES IN THE ADJUSTER NUT WITH A HAMMER (FIGURE 5, E).

G. HOLD THE ADJUSTER PLUG TO MAINTAIN ALIGNMENT OF THE HOLE WITH THE MARK.

PITMAN SHAFT OVER-CENTER PRELOAD ADJUSTMENT (FIGURES 6 THROUGH 8)

A. USING A 12 POINT SOCKET AND WRENCH, ROTATE THE STUB SHAFT FROM STOP TO STOP AND COUNT THE NUMBER OF TURNS. B. STARTING AT EITHER STOP, TURN THE STUB SHAFT BACK 1/2 THE TOTAL NUMBER OF TURNS. THIS IS THE "CENTER" OF THE GEAR. - WHEN THE GEAR IS CENTERED, THE FLAT ON THE STUB SHAFT (FIGURE 7, ITEM 40) SHOULD FACE UPWARD AND BE IN PARALLEL WITH THE SIDE COVER (FIGURE 7, ITEM A) AND THE MASTER SPLINE (FIGURE 6, ITEM B) ON THE PITMAN SHAFT SHOULD BE IN LINE WITH THE ADJUSTER SCREW (FIGURE 6, ITEM B). C. TURN THE PITMAN SHAFT ADJUSTER SCREW (FIGURE 6, ITEM B) COUNTER-CLOCKWISE UNTIL FULLY EXTENDED, THEN TURN BACK IN ONE FULL TURN. D. CHECK THE TURNING TORQUE OF THE STUB SHAFT USING AN INCH POUND TORQUE WRENCH AND 12 POINT SOCKET. PLACE THE TORQUE WRENCH, IN THE VERTICAL POSITION ON THE STUB SHAFT. ROTATE THE TORQUE WRENCH 45 DEGREES EACH SIDE OF THE CENTER OF THE STUB SHAFT AND RECORD THE HIGHEST DRAG TORQUE MEASURED ON OR NEAR CENTER (FIGURE 8). E. TURN THE ADJUSTER SCREW IN UNTIL THE TORQUE REQUIRED TO TURN THE STUB SHAFT IS 0.6 TO 1.2 N.M (6.0 - 10.0 LBS.IN.) GREATER THAN THE READING IN STEP "D". TIGHTEN THE ADJUSTER SCREW JAM NUT TO 50 N.M (37 LBS.FT.). 4. STEERING GEAR TO VEHICLE. - REFER TO "POWER STEERING GEAR REPLACEMENT" IN SECTION 3B OF THE APPROPRIATE M/L SERVICE MANUAL FOR COMPLETE INSTALLATION AND SYSTEM BLEED PROCEDURE.

SERVICE PARTS INFORMATION

PART NUMBER DESCRIPTION QUANTITY

26036745 VALVE ASSEMBLY 1

PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.

WARRANTY INFORMATION

FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR LABOR OPERATION DESCRIPTION TIME ADD

T7176 GEAR ASSEMBLY 1.3

0.2 W/STABILIZER BAR

0.1 W/HYDRAULIC BRAKE BOOSTER

0.2 TO REPLACE VALVE ASSEMBLY

FIGURES: 8

CAPTIONS: FIGURE 1 - INTEGRAL STEERING GEAR COMPONENTS FIGURE 2 - REMOVING THE ADJUSTER PLUG NUT FIGURE 3 - ADJUSTER PLUG VALVE ASSEMBLY FIGURE 4 - WORM AND VALVE ASSEMBLY BEARING FIGURE 5 - ADJUST THRUST BEARING PRELOAD FIGURE 6 - ALIGNING PITMAN SHAFT MASTER SPLINE FIGURE 7 - ALIGNING THE STUB SHAFT FIGURE 8 - CHECKING OVER-CENTER ROTATIONAL TORQUE

GENERAL MOTORS BULLETINS ARE INTENDED FOR USE BY PROFESSIONAL TECHNICIANS, NOT A "DO-IT-YOURSELFER". THEY ARE WRITTEN TO INFORM THOSE TECHNICIANS OF CONDITIONS THAT MAY OCCUR ON SOME VEHICLES, OR TO PROVIDE INFORMATION THAT COULD ASSIST IN THE PROPER SERVICE OF A VEHICLE. PROPERLY TRAINED TECHNICIANS HAVE THE EQUIPMENT, TOOLS, SAFETY INSTRUCTIONS AND KNOW-HOW TO DO A JOB PROPERLY AND SAFELY. IF A CONDITION IS DESCRIBED, DO NOT ASSUME THAT THE BULLETIN APPLIES TO YOUR VEHICLE, OR THAT YOUR VEHICLE WILL HAVE THAT CONDITION. SEE A GENERAL MOTORS DEALER SERVICING YOUR BRAND OF GENERAL MOTORS VEHICLE FOR INFORMATION ON WHETHER YOUR VEHICLE MAY BENEFIT FROM THE INFORMATION.

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