Steering Gear - Manual GMC Cab & Chassis R2500

DESCRIPTION & OPERATION

Steering gear is a recirculating ball type and consists of a ball nut connected to steering worm and in mesh with sector gear. Gears are basically the same for all models and service procedures will apply to all gears unless noted otherwise. Precision finished helical grooves within ball nut match helical grooves in worm. Ball bearings roll within grooves when steering wheel is turned. There are two complete circuits using tubular ball guides to deflect balls away from their helical path at one end of groove and guide them back to other end. When steering wheel is turned to right, nut moves upward; when turned to left, nut moves downward. The teeth on the sector (forged as part of pitman shaft) and the ball nut are so designed that a tighter fit exists between the two when the front wheels are straight ahead. Proper engagement between sector and ball nut is obtained by adjusting screw, which moves pitman shaft endwise, permitting desired engagement of tapered teeth of the ball nut and sector gear. Worm bearing adjuster can be turned to provide proper preloading of the upper and lower bearings.

PRELIMINARY ADJUSTMENT

Worm bearing preload adjustment MUST be made first; then, make over-center preload adjustment. DO NOT reverse the order of adjustment. Adjustment of steering gear can be made on or off vehicle in most cases. When making the worm bearing preload adjustment with gear on vehicle, the pitman arm must be disconnected or the steering linkage disconnected from the pitman arm. The torque wrench can be connected directly to the worm shaft (input shaft) or to steering wheel retaining nut (steering column drag is negligible). When making the over-center preload adjustment, torque wrench is attached to the sector shaft (after removing pitman arm) or the steering wheel nut.

WORM BEARING PRELOAD ADJUSTMENT

1. Loosen over-center preload adjuster screw. Tighten worm bearing adjuster until all end play has been removed; then loosen 1/4 turn and tighten lock nut. Turn worm shaft carefully to either stop. Do not jam into stop as damage to gear could result.
2. Rotate worm shaft back from stop about 1/2 turn. Using an INCH lb. torque wrench, measure the torque required to keep worm shaft in motion about one revolution.
3. Adjust rotating torque to specifications, using worm bearing adjuster. The worm bearing preload should be between 5-8 INCH Lbs. (.6-.9 N.m). Tighten lock nut, and recheck turning torque. Adjust as necessary. Proceed to Over-Center Preload adjustment procedure.

Adjustment Points for Steering Gear. Worm bearing preload must be adjusted before over-center preload. Scheme 1

OVER-CENTER PRELOAD ADJUSTMENT

1. With worm bearing preload adjusted, turn worm shaft slowly from stop-to-stop while counting total number of turns. Then, turn shaft half-way back to exact center position.
2. Loosen lock nut and turn over-center adjustment screws in until all lash is taken out of shaft. Tighten lock nut. Rotate worm shaft slightly off center (45-90°), then attach an INCH lbs. torque wrench to worm shaft.
3. Using torque wrench as a lever, rotate worm shaft back through center position and record rotating torque. Over-center rotating torque should be 16 INCH Lbs. (1.8 N.m). If rotating torque is not to specifications, repeat procedure.

Cross Section of Steering Gear. Scheme 2

TROUBLE SHOOTING

Refer to TROUBLE SHOOTING - BASIC PROCEDURES article in the GENERAL TROUBLE SHOOTING section.

REMOVAL & INSTALLATION

Scheme 3

1. Set front wheels in straight-ahead position. Remove flexible coupling-to-steering shaft flange bolts or lower universal joint pinch bolt. Mark position of universal yoke-to-worm shaft.
2. Mark relationship of pitman arm-to-sector shaft. Remove pitman arm using puller (J-6632). Remove steering gear mounting bolts and remove gear assembly.
3. Install flexible coupling on worm shaft aligning flat on coupling with flat on shaft. Push coupling on shaft until shaft hits shoulder. Install pinch bolt. The pinch bolt must pass through the shaft undercut.
4. Place gear in position, guiding coupling bolt into steering shaft flange. Install gear-to-frame bolts. Tighten bolt to specification.
5. If flexible coupling alignment pin plastic spacers are used, make sure they are bottomed on pins, then tighten flange bolt nuts and remove plastic spacers. Spacers aid in centering pins and maintain correct coupling-to-flange dimension. (Scheme 3): Adjusting Flexible Coupling for General Motors Models
6. Check that flexible coupling-to-steering shaft flange dimension is.250-.325" (6.35-8.25 mm). (Scheme 3) If flexible coupling alignment pin plastic spacers are not used, center pins in slots in steering shaft flange and tighten flange bolt nuts.

Note. Plastic spacers must be removed before driving vehicle.

SECTOR SHAFT SEAL

Note. For models not listed, seal replacement procedure was not available from manufacturer.

1. On 4WD models, gear must be removed from vehicle to replace seal. On all others, remove pitman arm from sector shaft. Rotate steering wheel from stop-to-stop while counting number of turns. Turn wheel back half way, placing gear at center of travel.
2. Remove bolts attaching side cover to housing, and lift sector shaft and side cover assembly from housing. Pry sector shaft seal from housing using a screwdriver. DO NOT scratch housing bore.
3. Inspect gear lubricant for contamination, if lubricant is contaminated in any way, gear should be completely overhauled. Lubricate new sector shaft seal with steering gear lubricant (GM 4673M). Position seal in sector shaft bore, and tap it into place using a socket.
4. Remove over-center adjuster lock nut. Remove side cover from sector shaft assembly by turning over-center adjuster screw clockwise. Install sector shaft in gear so center tooth of sector enters center tooth space of ball nut.
5. Fill gear housing with lubricant and install new side cover gasket on gear housing. Install side cover over sector shaft by reaching through cover hole with a screwdriver.
6. Turn over-center adjuster screws counterclockwise until screw bottoms; then back off screw 1/4 turn. Install over-center adjuster lock nut. Adjust worm bearing and over-center preload.

DISASSEMBLY

1. Place steering gear in a vise, clamping onto one mounting tab or a suitable holding fixture. Worm shaft should be in a horizontal position. Loosen over-center preload adjuster lock nut, and turn adjuster a few turns out.
2. Loosen lock nut on worm shaft adjuster, and turn adjuster out a few turns. Rotate worm shaft from stop-to-stop, counting number of turns. Then turn shaft back 1/2 the number of turns to center sector shaft.
3. Place a pan under assembly to catch oil, and remove 3 self-locking bolts holding side cover to the housing. Tap on end of sector shaft with a mallet and lift side cover and sector shaft assembly from gear housing.
4. If sector does not clear opening easily, turn worm shaft by hand until sector can be removed. Remove worm shaft adjuster and lock nut assembly with lower worm shaft bearing. CAUTION: DO NOT allow ball nut to run down to either end of the wormshaft as ball guide ends may be damaged.
5. Remove worm shaft and ball nut assembly from housing while housing is in a horizontal position to prevent ball nut from running down worm shaft. Remove upper bearing from worm guide.
6. Using screwdriver, pry lower bearing retainer from worm adjuster assembly and remove bearing. Remove over-center adjuster lock nut and screw.
7. Slide screw and shim out slot in end of sector shaft. Pry out and discard both sector shaft and worm shaft seals.

CLEANING & INSPECTION

Wash parts with clean solvent and blow dry with air. Inspect bearings and races for signs or wear. Any parts that show signs of wear should be replaced. Inspect sector shaft fit at side cover bushing. If bushing is worn, a new side cover and bushing assembly should be installed. Check ball nut and worm shaft assembly for wear and straightness.

Sector Shaft & Worm Shaft Seals

Using screwdriver, pry out seals. Before installing new seals, check condition of sector shaft bushings and upper worm shaft bearing race. Use a socket (pressing outer diameter of seal) to replace seal. Avoid installing seal in a cocked position.

Sector Shaft Bushing

Support steering gear in an arbor press. Drive sector shaft bushing from housing. Press new bushing into position. Replacement bushings are machined to size and need no reaming.

Worm Shaft Bearing Race (In Adjuster)

Remove worm shaft bearing race using a slide hammer or a hammer and punch. Press bearing in place using an arbor press.

Removing Worm Shaft Bearing Race from Adjuster. Install new race using arbor press. Scheme 4

Worm Shaft Bearing Race (In Housing)

Drive out housing bearing race with a hammer and punch. Press new race in using an arbor press.

Ball Nut & Worm Shaft Assembly

Ball nut disassembly is not necessary unless there is an indication of binding or tightness when rotating worm. If disassembly is required, proceed as follows

Scheme 5

1. This step will let loose about 50 ball bearings; be ready to catch them ALL. Remove clamp that retains ball guides and pull guides from ball nut while catching balls in clean pan. Turn nut over and rotate worm until all balls have fallen into pan.
2. Note relation of worm to ball nut and remove worm from ball nut. Wash parts and inspect worm, nut grooves, and ball bearings for indentations. Check ball guides for damage at ends where they deflect or pick up balls from helical path on worm.
3. To reassemble ball nut and worm shaft, insert ball nut over worm so that shallow end of ball nut teeth are on left side (looking from steering wheel end of worm shaft). Align grooves in worm and nut by sighting through ball guide holes.
4. There are 2 types of ball guides: those with holes in the middle and those with no hole. If ball guides have a hole in middle, insert ball guides into holes in ball nut. Divide balls into 2 equal groups. Insert each group into a ball guide, while slowly turning the worm shaft. (Scheme 5): Filling Ball Circuits Through Holes in Ball Guides. Rotate worm while installing balls.
5. If guides have no hole, separate the halves and fill half of each set with balls. Cover with the remaining half and plug the ends with grease to prevent balls from falling out.
6. Fill each circuit in ball nut with half of the remaining balls in one circuit, and half in the other. DO NOT turn worm shaft while installing. Insert ball guides. On both types, install ball guide retainer.

Filling Ball Circuits Through Holes in Ball Nut. Do not rotate worm while installing balls. Scheme 6

Exploded View of Recirculating Ball Steering Gear. General Motors model is shown. Scheme 7

Scheme 8

1. Place gear housing in a vise with worm shaft bore horizontal and side cover opening facing up. All seals, bushings, and worm shaft bearing races should be installed.
2. Slip upper ball bearing over worm shaft and insert worm and nut assembly into housing feeding end of shaft through upper ball bearing race and seal. Place ball bearing in adjuster race and press stamped retainer into place with a socket.
3. Install adjuster and lock nut into housing carefully guiding worm shaft into bearing until nearly all end play is removed from worm shaft. Position over-center adjuster (with shim) in slotted end of sector shaft.
4. Check end clearance, which should not exceed.002" (.05 mm). If clearance is greater than specified, a steering gear over-center adjuster shim kit is available.
5. Lubricate gear as follows: Rotate worm shaft until ball nut is at end of travel, while forcing as much grease as possible into housing without losing it out sector shaft opening. Rotate worm until ball is at other end, and apply more lubricant. (Scheme 8): Checking Over-Center Adjuster Clearance. Clearance should be.002" (.05 mm).
6. Rotate worm until ball is at center. This will help sector and ball nut engage properly. Insert sector shaft and over-center adjuster screw (without side cover) into housing so center tooth of sector teeth enters center tooth space in ball nut.
7. Apply more lubricant into housing. Install side cover gasket. Install side cover over sector shaft by reaching through cover with a screwdriver.
8. Turn over-center adjuster screw counterclockwise until screw bottoms; then back off screw 1/2 turn. Loosely install a new lock nut onto adjuster screw.
9. Install and tighten side cover bolts to specifications. Adjust worm bearing preload and over-center preload as previously outlined. See Adjustments in this article.

WHEEL ALIGNMENT

After completing appropriate service procedures, refer to appropriate WHEEL ALIGNMENT SPECIFICATIONS & PROCEDURES article in the WHEEL ALIGNMENT section below.

1. WHEEL ALIGNMENT SPECIFICATIONS & PROCEDURES (for Pickup)
2. WHEEL ALIGNMENT SPECIFICATIONS & PROCEDURES (for Van)

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS