wheel nut leaflet

8/14/2019 Wheel Nut Leaflet

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3. Wet tightening stabilizes the axial tension of the wheel bolt atthe target value.

Wet tightening is another critical point in tightening wheel nuts. Wet tightening is to

tighten wheel nuts with engine oil, wheel bearing grease or chassis grease apply-

ing lubricant to the threads of the nut and bolt. Why is wet tightening better than

dry tightening?

In the case of dry tightening, as the graph below shows, due to the variable friction

(coefficient of friction) of threads, the axial tension of the wheel bolt fluctuates to-

ward the lower limit even if the wheel nut is tightened to the specified torque. Thiscould lead to a situation where the wheel nut is thought to have been tightened

enough but it has not.

By contrast, wet tightening makes the nut threads have a lower friction and be

more stabilized due to the oil/grease on the threads. This reduces the fluctuation

in the axial tension of the wheel bolt and ensures that the wheel nut is securely

tightened when tightened to the specified torque.

(However, never use molybdenum disulfide based oil or grease because it causes

excessive tightening.) Also, even in the case of wet tightening, if the thread or nut

seat surface is damaged, the sliding of threads becomes poor, causing the same

problem as that of dry tightening. To prevent this, always check the threads of the

wheel bolt and nut and the nut seat surface of the wheel carefully before tighten-

ing wheel nuts.

Structure and oil application point for 8 stud bolts (JIS type) and 10

stud bolt wheel bol t (ISO type)

Wheel nut tightening torque vs. wheel bolt axial tensionFluctuation ofwheel boltaxial tensionin case of wettightening

Fluctuation ofwheel boltaxial tensionin case of drytightening

z C [ i b g t g

zC[{g

Dry tightening is

likely to make the

tightening force

insufficient.

Wheel nut tightening torque

Axialtensionofwheelbol

Brake drumWheelBrake drumWheel

Wheel

bolt

Wheel

nut

Wheel

bolt

HubWheel

nutHub

8 stud bolts (JIS type) 10 stud bolt wheel bolt (ISO type)

Oil application Oil application

Oil or grease must

NOT be applied to the

nut seat surface.


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4. Why must the wheel nuts be retightened?

Wheel nuts could become loose if they are removed and reinstalled when replac-

ing a tire or wheel. This is supported by experiment data that indicate a decline in

the axial tension of the wheel bolt after 50 to 100 km of travel. Especially, the de-

cline is relatively large if the axial tension was low when the wheel nut was tight-

ened. Why?

Because, in the case of a wheel that was removed and reinstalled or a new wheel,

the contact surfaces of the wheel and wheel nut are not the same as before, so

wheel nuts may appear to fully contact the wheel but are actually in partial contact.If the vehicle is driven in this condition, early familiarization occurs in the partial

contact area, the axial tension of the wheel bolt lowers and the wheel nut is easily

loosened. Please be sure to retighten wheel nuts after 50 to 100 km of travel,

once wheel nuts were loosened fo r any reason.

5. Check points when tightening wheel nuts

Following is summarized check points when tightening wheel nuts:

1. Maintain the specified tightening torque (use a torque wrench.)

2. Tighten nuts in the wet state (oil/grease applied where speci-

fied).

.

3. Clean the threads of wheel nuts and bolts and areas surround-

ing the wheel fitting hole completely, and thoroughly checkthem for damage before tightening wheel nuts.

4. Tighten wheel nuts, two or three times for each, in diagonal

order.5. After removing and reinstalling a wheel, or replacing it with a

new one, be sure to retighten the wheel nuts after 50 to 100 km

of travel. Subsequently, retighten them at each scheduled pe-

riodical inspection or whenever necessary

Familiarization after initial running and change of wheel bolt

axial tension

At tention!

(Whe

elnuttighteningtorque) Retightening required!

Wheelboltaxialtension

Strictly observe these check points to avoid the risk of wheel

bolts breaking and the wheel falling off .If axial tension (tight-

ening torque) is low,its reduction is large. For light-duty trucks and buses (Canter, Rosa, etc.), dry tightening

(without engine oil/chassis grease applied to threads, etc.) is the

manufacturers specification, and the tightening torque and tightening

method differ according to the model and type. For details, see the

Owners Handbook or relevant shop manual. Distance traveled after wheel

replacement (km)

0 1,000 2,000

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