Shifting is the most common malfunction of manual transmissions. Shifting in a low-profile manual transmission occurs when the clutch is in normal condition but the transmission engages two gears simultaneously, or when a different gear is engaged when the desired gear is engaged. The causes of this malfunction are rare, and consequently, the methods and solutions for its elimination are also much fewer. First, interlocking mechanism failure: This can occur due to excessive wear of the shift fork shaft, interlocking pin, or interlocking steel ball. Second, excessive wear on the curved working surface at the lower end of the shift lever or on the groove of the shift block on the shift fork shaft.
Third, a broken shift lever ball retaining pin or excessive wear and tear on the ball hole or ball head can also cause shifting in a low-profile manual transmission. In short, the primary cause of shifting in a low-profile manual transmission is a malfunction in the transmission's operating mechanism. With these three points in mind, let's diagnose and troubleshoot each one accordingly. (1) When the gear is required, another gear is selected: shake the gear lever and check its swing angle. If it is beyond 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 being disengaged from the groove (the reason for the disengagement is wear of the arc working surface at the lower end or wear of the guide groove). (3) When 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 engaged smoothly when shifting gears, and gear collision often occurs. Synchronizer failure is one of the causes. Pull up the parking brake handle to park the low-bed truck reliably. Start the engine, let it idle, press the clutch pedal, and shift to first gear or reverse. Check for any noise and smooth shifting. If there is noise or uneven shifting, it indicates that the lowbed truck's clutch is not disengaging completely. In this case, the vehicle needs to be inspected, including checking the clutch pedal's free travel, clutch operation, and the clutch fluid level. By doing this, we can identify the cause and resolve the issue.
After repairing the lowbed truck's clutch hydraulic system, air may enter the piping. Air may also enter the hydraulic system when adding brake fluid. This air entry shortens the master cylinder push rod stroke (i.e., the pedal's operating travel), preventing the lowbed truck's clutch from disengaging completely. Therefore, after repairing the hydraulic system or if air is suspected, it is important to remove the air from the system. There are six specific methods for eliminating the problem. Let's analyze them one by one:
(1) Add brake fluid to the master cylinder reservoir to the specified height and raise the low-bed truck;
(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 work together to bleed 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 again;
(4) Repeat the above method several times until no bubbles are seen in the outflowing brake fluid;
(5) After the air is completely eliminated, it is necessary to check and adjust the free travel of the pedal again;
(6) This is the last step. Check the fluid level in the master cylinder reservoir again. If the level is not high enough, add more.
