Detection
In order to quickly attenuate the vibration of the frame and body and improve the smoothness and comfort of the car's driving, shock absorbers are generally installed on the car suspension system. The car widely uses double-acting cylinder shock absorbers.
Shock absorber detection includes shock absorber performance test, shock absorber durability test, and shock absorber double excitation test. Perform dynamometer test, friction test, temperature characteristic test, etc. on various types of shock absorbers.
First, drive the car on a road with poor road conditions for 10km and then stop. Touch the shock absorber shell with your hand. If it is not hot enough, it means that there is no resistance inside the shock absorber and the shock absorber does not work. At this time, you can add appropriate lubricating oil and then test it. If the shell is hot, it means that the shock absorber is short of oil inside and should be filled with enough oil; otherwise, it means that the shock absorber has failed.
Second, press the bumper hard and then release it. If the car jumps 2~3 times, it means that the shock absorber is working well.
Third, when the car is driving slowly and emergency braking, if the car vibrates violently, it means that there is a problem with the shock absorber.
Fourth, remove the shock absorber and stand it upright, clamp the lower end connecting ring on the vise, and pull and press the shock absorber rod several times. There should be stable resistance at this time. The resistance to pull up (recovery) should be greater than the resistance when pressing down. If the resistance is unstable or there is no resistance, it may be that the shock absorber is short of oil or the valve parts are damaged. Repair or replace the parts.
Repair
After determining that the shock absorber has a problem or fails, you should first check whether the shock absorber is leaking oil or has traces of old oil leakage.
The oil seal gasket and sealing gasket are broken and damaged, and the oil storage cylinder head nut is loose. It may be that the oil seal and sealing gasket are damaged and failed, and new seals should be replaced. If the oil leakage still cannot be eliminated, the shock absorber should be pulled out. If you feel that there is a card or the weight is different, further check whether the gap between the piston and the cylinder is too large, whether the shock absorber piston connecting rod is bent, and whether the piston connecting rod surface and the cylinder are scratched or pulled.
If the shock absorber does not leak oil, check whether the shock absorber connecting pin, connecting rod, connecting hole, rubber bushing, etc. are damaged, desoldered, cracked or detached. If the above inspection is normal, the shock absorber should be further disassembled to check whether the matching clearance between the piston and the cylinder is too large, whether the cylinder is strained, whether the valve seal is good, whether the valve disc fits tightly with the valve seat, and whether the extension spring of the shock absorber is too soft or broken. Repair it by grinding or replacing parts according to the situation.
In addition, the shock absorber may make a sound during actual use. This is mainly caused by the collision between the shock absorber and the leaf spring, frame or shaft, damage or detachment of the rubber pad, deformation of the shock absorber dustproof cylinder, insufficient oil, etc. The cause should be found out and repaired.
After inspection and repair, the shock absorber should be tested for working performance on a special test bench. When the resistance frequency is 100±1mm, the resistance of its extension stroke and compression stroke should meet the requirements. For example, the maximum resistance of the extension stroke of Jiefang CAl091 is 2156~2646N, and the maximum resistance of the compression stroke is 392~588N; the maximum resistance of the extension stroke of Dongfeng is 2450~3038N, and the maximum resistance of the compression stroke is 490~686N.
If there are no test conditions, we can also use an empirical method, that is, use an iron rod to penetrate the lower end of the shock absorber, which indicates that the shock absorber is basically normal.