Repair of the steering mechanism ZIL-131

Steering Gear Disassembly

Disassembly and assembly of the steering gear, as well as the pump, should be carried out only if necessary by qualified mechanics in conditions of complete cleanliness

Before disassembly, the steering mechanism must be removed from the vehicle, for which you should:

• - unscrew the nut 37 (see Fig. 1) and remove the bipod with a puller: knocking off the bipod can cause parts to break;
• - unscrew the plug with a magnet and drain the oil; for a more complete drain, turn the steering wheel 2-3 times from one extreme position to another;
• - disconnect the hoses, drain the remaining oil in the pump;
• - disconnect the cardan shaft by removing the cotter pin, unscrewing the wedge nut 9 (see Fig. 2) and knocking out the wedge;

• - unscrew the five bolts securing the steering gear housing to the frame;
• - thoroughly clean and rinse the outer surface of the steering mechanism;
• - drain the remaining oil by turning the steering mechanism with the valve down and turning the screw 2-3 times from one extreme position to another.

Disassembly and check of the steering gear should be done in the following order:

• 1. Remove the side cover together with the bipod shaft by unscrewing the seven bolts.
• When removing the bipod shaft, it is necessary to clean its splined end and be careful not to damage the oil seal and O-ring.
• 2. Remove the top cover by unscrewing the four bolts; when removing the cover, be careful not to damage the stuffing box and O-ring.
• 3. Remove the control valve body with screw, piston rail and intermediate cover by unscrewing the six bolts.
• 4. Remove the bottom cover by unscrewing the six bolts.
• 5. Check tightness of thrust ball bearing nut.

The torque required to turn the control valve body relative to the screw should be 6-8.5 kgcm.

• 6. If the conditions specified in point 5 are not observed, adjust the tightening of the nut or, if the ball bearings are damaged, replace them.

To adjust the tightening of the nut, first press the collar of the nut pressed into the groove of the screw, protecting the screw thread from damage, unscrew the nut, clean the groove in the screw and the thread in the nut.

The conical disc spring must be installed between the ball bearing and the nut with the concave side towards the ball bearing.

After adjusting the tightening of the nut, its shoulder must be pressed without breaking into the groove of the screw; the extrusion should be rounded, without sharp corners.

• 7. Check the axial movement of the adjusting screw 30 (see Fig. 1) in the bipod shaft. If the movement exceeds 0.15 mm, replace the shim 27, bringing the movement to a value of 0.02-0.08 mm.
• 8. Check if there is any axial movement of the ball nut relative to the piston rack. If necessary, tighten or replace the two set screws and punch them out.
• 9. Check the fit of the ball nut on the middle part of the screw. The rotation of the nut on the screw must occur without jamming, and the axial movement relative to the screw must not exceed 0.3 mm.
• 10. In case of non-compliance with the conditions specified in paragraph 9, replace the balls or the entire set (ball nut and screw with balls), for which:
• a) unscrew the two set screws 42 that secure the ball nut using a special wrench with a sufficiently large shoulder;
• b) remove the ball nut with the screw from the piston rail, keeping the grooves and balls from falling out;
• c) remove the grooves and, turning the screw relative to the nut in one direction or the other, remove the balls;
• d) remove the intermediate cover.
• 11. If the helical grooves of the nut or screw are damaged, replace them.
• 12. In case of replacement of a set - a nut and a screw with balls - their completeness during assembly must not be violated, since they are selected individually at the factory.
• 13. In case of replacing only balls with a larger size, take balls of the same size group (with a difference in size not more than 0.002 mm).

Installing balls with a difference in size of more than 0.002 mm can lead to breakage of the balls and jamming of the steering.

See below for how to assemble the ball nut.

• 14. After replacing the balls, the nut should turn in the middle part of the screw under the action of a torque of 3-8 kg / cm, and the fit should be free at the edges of the screw

Steering mechanism assembly

• 1. Before assembly, all parts must be thoroughly washed and dried. Do not wipe the parts with ends with rags that leave threads, villi, etc. on the parts.
• 2. All rubber sealing parts must be inspected and, if necessary, replaced.
• 3. The tightening torque should be equal to 2.1-2.8 kgm for MB bolts and 3.5-4.2 kg / m for M10 bolts.
• 4. The piston rings must move freely in the grooves.
• 5. To assemble a ball nut you need:
• a) put on the screw an intermediate cover and a nut, install the nut on the lower end of the screw, which does not have a shoulder, aligning the holes of the nut, which include grooves 9 (see Fig. 1), with the helical groove of the screw;
• b) put 23 balls through the hole in the nut facing the shoulder of the screw, turning the screw counterclockwise; put eight balls into grooves folded together and prevent them from falling out by covering the exits with UE grease (technical petroleum jelly), GOST 782-59;
• c) put the grooves with balls into the nut, turning the screw if necessary; wrap around the nut to prevent the grooves from falling out of the nut;
• d) check the torque of the nut on the middle part of the screw and, if necessary, replace the balls;
• e) screw the set screws 42, tightening them with a torque of 5-6 kGm, and punch each screw in two places against the grooves in the piston-rack.

If the groove in the piston rail matches the slot of the screw, the latter must be replaced.

The protrusion of screws or bulges above the cylindrical surface of the piston-rack is unacceptable, as it causes scuffing of the hydraulic booster cylinder.

Piston ring locks should be positioned at 900, and mounted symmetrically at the top of the cylinder.

• 6. During disassembly, the completeness of the spool of the jet plungers and the control valve body must not be violated, since they are individually selected at the factory.

In the case of overhauling the control valve, it is necessary to ensure that the recess on the end of the spool faces upwards from the middle shoulder of the screw, and the chamfers on the reactive plungers 40 are outward.

The spool and reactive plungers must move smoothly in the control valve body, without jamming.

• 7. In the case of replacing the needle bearing 21 of the upper cover, it must be pressed in so that after pressing the marking on its end face is visible.
• The bearing needles must move freely in the bearing cage after pressing.
• 8. During assembly, the bipod shaft seal must be protected from damage by shaft splines.

The final fitting of the gland 34 of the bipod is carried out together with the thrust ring 35, the cuff 36, the washer and the retaining ring until the retaining ring snaps into the groove.

The retaining ring must fit into the crankcase groove all around.

• 9. In the assembled steering mechanism, after turning the steering screw 7 until the piston stops in both directions, apply an additional torque to the screw, achieving its movement in the axial direction.
• Springs 39 must ensure its return to its original position.
• 10. Adjust the adjusting screw 30 so that when passing through the middle position, the torque of the screw 7 is greater than the same torque before adjustment by 10-15 kgcm.

In this case, the moment when passing through the middle position should be no more than 50 kg / cm.

After adjusting screw 30, lock it with a locknut with a torque of 4-4.5 kGm and then check the turning moment of the steering screw again.

• 11. The rotation of the bipod shaft from one extreme position to another should occur when a moment of no more than 8 kGm is applied to it.