Before installing the demultiplier with a spacer on the crankcase of the main box and the spacer on the crankcase of the demultiplier, apply the anaerobic sealing compound UG-6 TU 6-01-1285-84 to the gaskets on both sides with a continuous strip 2-3 mm wide along the contour

Peculiarities of assembling the YaMZ-238VM gearbox

When installing the input shaft bearing cap (Fig. 1), the range gear with spacer on the main box crankcase (Fig. 2), the rear bearing cap of the range output shaft (Fig. 3), ensure minimum axial play of the shafts using shims, selected as follows:

Measure the dimension "A" of the depth of the groove for the bearing in the bearing cap, taking into account the thickness of the gasket, with an accuracy of 0.1 mm (Fig. 1).

Measure dimension "B" from the end face of the outer ring of the bearing to the surface of the crankcase wall with the bearing pressed to the stop with an accuracy of 0.1 mm.

Select the total nominal thickness of shims S from the condition: S = [A - B - (0.2…0.3)]mm

Peculiarities of assembling the YaMZ-238VM gearbox

Measure dimension "A" (Fig. 2) from the end of the outer ring of the bearing to the surface of the crankcase with an accuracy of 0.1 mm, making sure that the centering ring is pressed in to the stop, and the spring ring and bearing are firmly pressed against the central ring.

Measure the dimension "B" of the depth of the groove for the bearing in the gear coupling, taking into account the spacer and the groove with an accuracy of 0.1 mm.

Select the total thickness of the shims S from the condition S = [B - A - (0.2 ... 0.3)] mm

Peculiarities of assembling the YaMZ-238VM gearbox

Measure dimension ″B″ (fig. 3) from the end face of the bearing outer ring to the crankcase surface to the nearest 0.05 mm, making sure that the snap ring and bearing are firmly pressed against the crankcase surface.

Measure the dimension ″Г″ from the gasket to the thrust ring in the undercut of the cover with an accuracy of 0.05 mm.

Select the total nominal thickness of shims S from the condition: S = [D - V - (0.15 ... 0.2)] mm

Tighten the bolts for fastening the crankcase in two steps (see the table "Torques").

JaMZ-238VM gearbox assembly features

Tightening sequence according to fig. 4.

When repairing the range-switch with the replacement of synchronizer parts, adjust the required rod stroke when the higher range is turned on, ensuring that the fork crackers are unloaded when working at the highest range, for which:

1. Switch on the upper range in the demultiplier by supplying air under pressure from 784 to 833 kPa (8...8.5 kgf/cm2 ) into the rear cavity of the pneumatic cylinder full engagement.

When fully engaged, the indicator lamp should go out. The driveshaft mounting flange should not turn by hand.

2. Screw the adjusting bolt into the piston rod until it stops (when turning the bolt, an increase in resistance to rotation should be felt).

Repeat the operation several times, making sure that the stop is felt at the same position of the bolt head.

3. Turn the adjusting bolt from the position of its stop to the end by one turn (5 faces of the head) and, holding it in this position, lock it with a lock nut, tightening it with a torque of 137-157 N m (14-16 kgf cm).

After adjustment, the driveshaft mounting flange should turn easily without jamming, by hand. Turn the flange through an angle of at least 360˚.

Attention! Incorrect adjustment causes an overload of the range fork crackers, which leads to their rapid destruction.

4 Installation of the demultiplier on the gearbox should be carried out with the axes of the shafts of the main gearbox in the vertical position.

The output shaft of the demultiplier must be rotated by hand with any range engaged and gears disengaged in the main box.

Possible malfunctions of the YaMZ-238VM gearbox and how to eliminate them

Problem Remedy

Difficult shifting

Incomplete clutch disengagement (clutch"leads"):

  • - Adjust the free play of the clutch pedal or, if the defect is due to a malfunction of the clutch parts, replace the damaged parts
  • - Synchronizer worn or damaged - Replace defective synchronizer
  • - Gear teeth damaged - Replace damaged parts

Increased noise during gearbox operation

Insufficient oil in the gearbox - Fill oil up to the level of the control hole

Worn transmission shaft bearings - Replace defective bearings

Increased gear tooth wear - Replace worn gears

Spontaneous disengagement of gears when the car is moving

Uneven wear of gear teeth - Replace defective parts

Increased wear on gearbox shaft bearings - Replace defective bearings

Faulty shift rod locks - Replace faulty parts

Spontaneous switching off of ranges in the demultiplier

Compressed air flow into the cylinder cavity opposite to the engaged gear - Replace the defective o-rings of the spool and the intake valve of the air distributor

Increased wear of the fork lugs - Replace the lugs and adjust the stroke.

Non-activation or delayed inclusion of ranges in the demultiplier with the neutral position of the lever of the main box. The indicator lamp does not go out for a long time, air exits through the breather of the air distributor

Inlet valve rubber wear - Replace worn valve

Inlet valve spring broken - Replace defective spring

Worn inlet valve O-ring - Replace O-ring

Irregular fit of the inlet valve to the body - Replace defective parts

Inlet valve sticking in the out position - Clean and lubricate the inlet valve stem, polish if necessary

Worn or hardened seals of the piston of the working cylinder - Replace the seals of the piston

Non-activation or delayed inclusion of ranges in the demultiplier when the lever is in neutral position
The indicator lamp does not go out for a long time, air escapes through the breather of the top cover

Damage diffuser diaphragm - Replace damaged diaphragm

Worn or hardened O-rings of the slave cylinder in the hole for the shift fork rod - Replace the O-ring

Air passage through the air distributor breather with the gear engaged in the main box

Intake valve rubber wear - Replace valve

Loose fit of tappet to inlet valve - Replace faulty parts