The phenomenon of random gear shifting is the most common fault phenomenon of manual transmission. The phenomenon of random gear shifting of low-plate manual transmission refers to the situation that when the clutch is in normal technical condition, the transmission is in two gears at the same time, or it is in another gear when the required gear is shifted. There are few reasons for this fault, so correspondingly, its elimination methods and solutions are also much less.
First, the interlocking device fails: such as excessive wear of the fork shaft, interlocking pin or interlocking steel ball. Second, the arc-shaped working surface at the lower end of the shift lever is worn too much or the groove of the shift block on the fork shaft is worn too much.Third, the breakage of the positioning pin of the ball head of the shift lever or the loose wear of the ball hole and the ball head will also cause the phenomenon of low-plate manual transmission skipping. In short, the main reason for random gear shifting is the failure of the transmission control mechanism. With the above three points of analysis, we will diagnose and eliminate them one by one.
(1) When the gear is required, another gear is selected: shake the gear lever and check its swing angle. If it exceeds the normal range, the fault is caused by the loose fit between the ball head positioning pin and the positioning groove at the lower end of the gear lever or excessive wear of the ball head and the ball hole.
If the gear lever of the manual transmission of the flatbed truck swings 360 degrees, the positioning pin is broken.
(2) If the swing angle is normal, but the gear cannot be engaged or disengaged, the fault is caused by the lower end of the gear lever coming out of the groove (the reason for the disengagement is the wear of the arc working surface at the lower end or the wear of the guide groove).
(3) Two gears are engaged at the same time: the fault is caused by the failure of the interlocking device. Difficulty in shifting gears means that the clutch is in good technical condition, but the gear cannot be smoothly engaged when shifting gears, and gear collision sounds often occur. Synchronizer failure is one of the causes.
The low-bed truck can be parked reliably and the parking brake handle is pulled up. Start the engine, let the engine run at idle speed, step on the clutch pedal, shift to 1st gear or reverse gear, and check whether there is noise and whether the gear shift is smooth. If there is noise or the gear shift is not smooth, it means that the clutch of the low-bed transporter is not completely separated. At this time, it is necessary to check the vehicle, including checking the clutch pedal free travel, checking the working condition of the clutch, checking the liquid level of the clutch reservoir, etc. Through these aspects, we can find out the cause and solve it.
After the low-bed transporter clutch hydraulic control system is overhauled, air may enter the pipeline; when adding brake fluid, air may also enter the hydraulic system. After the air enters, the master cylinder push rod stroke, that is, the working stroke of the pedal, is shortened, so that the clutch of the low-bed transporter is not completely separated. Therefore, after the hydraulic system is overhauled or when it is suspected that the hydraulic system has entered air, the air in the hydraulic system must be removed. There are six specific methods for eliminating the problem. Let’s analyze them one by one:
(1) Add the brake fluid in the master cylinder reservoir to the specified height and raise the low-bed transport vehicle;
(2) Install a hose on the bleed valve of the working cylinder and connect it to a container containing brake fluid;
(3) It takes two people to exhaust the air. One person slowly presses the clutch pedal several times, and when resistance is felt, keep pressing it. The other person loosens the bleed valve until the brake fluid starts to flow out, and then tightens the bleed valve;
(4) Repeat the above steps several times until no bubbles are seen in the outflowing brake fluid;
(5) After the air is exhausted, check and adjust the free travel of the pedal again;
(6) This is the last step. Check the height of the liquid level in the master cylinder reservoir again. If the height is not enough, add more.
