233 

 

No. 171 Power-assisted pump with abnormal sound   

Malfunction Causes 

Solution 

1. Power-assisted oil insufficient   

Check power-assisted oil is insufficient; if so, add it;   

2. Power-assisted pump belt pulley loosening   

Check power-assisted pump belt pulley is loosening; if 
so, replace it;   

3. Power-assisted pump belt loosening or severely 
worn  

Check power-assisted pump belt is loosening or 
severely worn; if so, adjust or replace it;   

4. Screws of power-assisted pump loosening   

Check screws of power-assisted pump are loosening; if 
so, fasten them.   

Power-assisted 
pump with 
abnormal sound 
after vehicle 
started; and 
worsen when 
steering  

5. Power-assisted pump worn or damaged 
internally;  

Check power-assisted pump is worn or damaged 
internally; if so, replace it.   

 

Steering power insufficient 

Adjust or replace 

Power-assisted steering pump belt too loosening or 
damaged 

Lack of power steering oil 

Fill 

Power steering pump damaged 

Power steering gear damaged 

Replace 

Replace 

Abnormal 

Lack 

Damaged 

Damaged 

Normal 

Normal 

Normal 

 
 

 

 

234 

 

Add 

Power-assisted pump with 
abnormal sound 

Power-assisted oil insufficient 

Fixed screws of power-assisted pump 
loosening 

Fasten 

Replace 

Power-assisted pump belt pulley loosening or 
worn 

Replace 

Power-assisted pump belt loosening or worn 

Replace 

Power-assisted pump severely worn internally 

Lack 

Damaged 

Damaged 

Damaged 

Loosening 

Normal 

Normal 

Normal 

Normal 

 
 

 

 

235 

 

No. 172 Direction running out   

Malfunction Causes 

Solution 

(1) Front wheel’s rotating mass (including tire, hub, 
brake drum or disk, hub, etc.) imbalanced;   

Dynamic balancing of front wheel   

(2) Front wheel’s radial circle or end face circle running 
out too large;   

Positional adjustment for tire, dynamic balancing of 
the wheel 

(3) Front wheel using retread tire;   

Replace tire   

(4) Front wheel’s camber angle too small, toe-in too 
large, kingpin negative caster or caster angle too large;

Adjust toe-in or four-wheel positioning   

(5) Kingpin caster angle or kingpin angle inconsistent 
for two front wheels;   

Four-wheel positioning 

(6) Front beam or front suspension bent, distorted, 
deformed;  

Correct front body or replace front suspension   

(7) Action of steering system and front suspension 
interferes each other;   

Correct toe-in; adjust tie-rod; replace tie-rod, ball 
head 

(8) Steering system’s rigidity too low (including 
steering tie-rod, lower swing arm, etc.); 

Replace steering tie-rod, lower swing arm;   

(9) Meshing clearance of drive, driven parts or bearing 
clearance of steering engine too large;   

Adjust clearance;   

(10) Gear rack of steering engine matched 
looseningly;  

Adjust matching clearance;   

(11) Ball head of inner and outer steering tie-rods 
connected looseningly;   

Replace ball head;   

(12) Front support loosening or deformed;   

Fasten or replace front support   

(13) Front wheel hub bearing loosening;   

Replace bearing   

(14) Steering engine looseningly connected at the 
frame;  

Fasten or adjust   

(15) Vibration damper of front suspension fails or its 
efficiency at left and right different;   

Replace vibration damper   

(16) Front suspension height or rigidity (thickness, 
length, or extent of new, old of spring surface) 
inconsistent;  

Replace spring   

When the vehicle 
is running within 
certain low or high 
speed range, 
sometimes angular 
oscillation occurs 
around kingpin at 
two front wheels, 
as called front 
wheel yawing; 
especially when 
yawing at high 
speed, two front 
wheels are 
severely 
pendulating left to 
right, and hands 
holding steering 
gear feels sense of 
numbness, or even 
whole nose is seen 
to be shaking from 
the cab.   
 

(17) Road roughness too large; when blow frequency 
of road surface on the wheel is inconsistent with 
natural frequency of angular oscillation of front beam, 
yawing of front wheel is caused under gyroscope 
effect;  

Drive on favorable road surface   

 

 
 

 

 

236 

 

 

Diagnosis flowchart of front-wheel yawing