Power Steering Gear Service

Fig. 4 Power steering gear exploded view:

Disassembly

1. Remove adjusting locknut, then side cover bolts and turn in adjusting bolt 2 or 3 turns.
2. With gear in neutral (center) position, tap bottom of cross shaft with plastic hammer to remove shaft.
3. Remove valve housing nut using tool No. MB990667 for large gear and No. MB990852 for small gear, then valve housing bolts. While holding rack piston to avoid rotation, remove valve housing and rack piston.

Fig. 5 Measurement of rack piston backlash:

4. Secure valve housing in vise with dial indicator as shown, then move rack and piston up and down to check backlash between groove of rack piston and the balls. Backlash should be 0.0039 inch for large gear and 0.080 inch for small gear maximum. Measure backlash with piston fully tightened and loosened 2 turns. If backlash exceeds limit, replace ball screw unit and rack piston as an assembly.
5. Remove rack piston from valve housing by turning counterclockwise. Do not lose any of the 26 balls.

Fig. 6 Removal of top cover:

6. Remove top cover of valve housing using tool No. MB990853 for small gear or special spanner wrench as shown.

Fig. 7 Components of rack piston:

7. Remove circulator holder, circulator, seal ring and O-ring from rack piston.
8. Remove thrust unit, thrust needle roller bearing, seal rings and O-rings from input worm unit.
9. To disassemble subassembly components, proceed as follows:
a. Turn in adjusting bolt at tip of cross shaft and remove side cover. Do not lose any needle bearing rollers.
b. Remove adjusting bolt and plate, O-ring and needle bearing from side cover. Do not remove O-ring and sealing at rear of needle bearing if no oil leaks from thread of adjusting bolt. Also, do not remove bleeder plug unless necessary.
c. Remove seal ring and O-ring from valve housing.
d. Remove ball bearing and oil seal from top cover.
e. Remove snap ring at bottom of gearbox, then back-up ring and oil seal. Pull out seal housing.
f. Remove seal ring and O-rings from seal housing.
10. To assemble subassembly components, proceed as follows. Replace O-rings, seal rings and oil seals whenever disassembled.
a. Apply thin coat of multi-purpose grease to bearing surface of needle bearing and install rollers into side cover, then apply grease to bottom of side cover.
b. Insert adjusting bolt and plate into "T" slot on top of cross shaft, and adjust play to 0-.002 inch by selecting proper adjusting plate. When installing adjusting plate, place chamfered portion of plate to contact surface of cross shaft.
c. Install O-ring into side cover.
d. Align cross shaft with side cover and tighten with adjusting bolt, then tighten lock bolt temporarily.
e. Apply thin coat of multipurpose grease to lip of oil seal and press into top cover, then press fit ball bearing.
f. Apply thin coat of ATF to O-ring and seal ring, then insert into seal housing. Install seal housing straight into gear box with O-ring side positioned near mainshaft.
g. Apply thin coat of multipurpose grease to lip of oil seal, then press into gear box using tool No. CT-1008. Install back-up ring and snap ring.

Assembly

1. Apply thin coat of ATF to input worm unit O-rings and install O-rings and seal rings alternately onto worm unit. Do not apply excessive force.
2. Install thrust plate, thrust needle bearing and thrust plate to both ends of worm unit in that order, then apply thin coat of ATF to each.
3. Install O-ring and seal ring into groove of valve housing and apply thin coat of ATF to each.

Fig. 8 Tightening of top cover:

4. Install input worm unit into valve housing, then O-ring into top cover and top cover with bearing and oil seal onto valve housing. While turning worm unit, tighten by using spring scale and special spanner wrench as shown. Rotate worm unit to check for uniform movement.
5. Install valve housing nut and tighten temporarily using tool No. MB990667 for large gear and No. MB990852 for small gear. Do not allow top cover to rotate. The final tightening will occur during total starting torque measurement later in assembly procedure.
6. Measure starting torque by using tool No. CT-1108 and torque wrench while turning input worm unit, ensure preload is 3.5-6.9 in. lbs. If necessary, readjust by loosening valve housing nut as in steps 4-5.
7. Install O-ring and seal ring to rack piston and apply thin coat of ATF to each.
8. Install rack piston into worm shaft until piston contacts worm shaft end, then insert 19 balls into groove through 2 openings on top of piston. Do not rotate worm unit and piston while inserting balls. Do not allow hole to offset or turn during insertion of balls so balls will not fall into wrong groove. After insertion of all balls, ensure balls reach approximately 0.080 inch for large gear, or 0.5 inch for small gear below end of piston. Excessive clearance is an indication that a ball has fallen into wrong groove. If so, remove rack piston and insert balls.
9. Insert 7 balls into rack piston circulator. Apply multipurpose grease to balls to prevent them from falling from circulator. Install circulator and holder into rack piston.
10. Secure gear box in vise, then install valve housing and rack piston assembly into gear box and torque bolts to 33-40 ft. lbs. After installation, rotate assembly to move rack piston to neutral (center) position. Do not force rack piston into gearbox as seal ring may be damaged.
11. Apply thin coat of ATF to teeth and shaft of rack piston and multipurpose grease to oil seal lip of gear box, then install cross shaft assembly into gearbox and torque side cover bolts to 33-40 ft. lbs.

Fig. 9 Measurement of total starting torque:

12. Measure total starting torque of input worm shaft at neutral (center) position using tool No. CT-1108 and adjust to 3.6-7.1 in. lbs. for large gear or 4.3-7.8 in. lbs. for small gear by turning adjusting bolt. Torque valve housing nut to 130-166 ft. lbs. using tool No. MB990667 for large gear or No. MB990852 for small gear. Check input worm shaft for smooth rotation throughout its operation range.

Fig. 10 Installation position of Pitman arm:

13. Align slit of cross shaft with marking of pitman arm and install pitman arm, then torque nut to 94-108 ft. lbs. Check clearance between center of gearbox bolt and pitman arm. Clearance should be 0.77 inch.