Heavy Truck Gearbox Failure Analysis

Problems with the Gearbox

Fuller rt11509c gearbox installed in sinotruk Steyr are often suddenly found to have only high speed gears and no low speed gears, or only low speed gears and no high speed gears. In fact, this failure occurs when the truck is running in low gear and shifts to high gear, and still ends up running in low gear. For example, when the truck is driving in 4th gear and shifted to 5th gear, the result shows the working status of the low gear of the gearbox.

The solution of Gearbox failure one

This fault usually occurs in the control system of high and low gear shifts of the auxiliary box.

In case of such failure, the driver should first pull the pneumatic vehicle aside to stop. The specific inspection method is to first check whether the air pressure of the whole vehicle meets the requirements, and then place the gear lever in the neutral position; Move left and right back and forth in the high and low gear areas to observe whether the double-h shift valve on the upper cover of the gearbox has a “click, click” bleeding sound.
If there is no response, check whether the pressure-reducing valve of the shift air circuit is blocked or the air pressure output through the pressure-reducing valve is too low. If so, clean or replace the pressure-reducing valve. If the exhaust port of the double-h shift valve continues to exhaust outward when the shift lever is shifted from low gear to high gear, it is obvious that there is low gear but no high gear when the gas vehicle is driving.

The solution of Gearbox failure two

if the exhaust port of the double-h shift valve continues to exhaust outward when the shift lever is shifted from the high-speed range to the low-speed range, the vehicle has a high-speed range but no low-speed range during operation. In case of such a fault, the shift lever can be moved repeatedly in the left and right (high-speed and low-speed) positions of the neutral position, and the fault is often eliminated. This is due to the occasional loose sealing and air leakage of the “O” seal ring of the double h shift valve. Shift the gear lever several times in the high and low range. That is, it will be solved by repeatedly moving the double h shift valve core.
If repeatedly pulling the shift lever is invalid, it indicates that the double-h shift valve leaks or the high and low shift cylinders leak. Whether the double h shift valve leaks or the high and low shift cylinders leak, it will cause the failure of high gear without low gear, or low gear without high gear.

The method to check the air leakage

If the transmission has a low gear but no high gear, push the shift lever from the low gear area to the high gear area, and then remove the air inlet connector of the low gear shift cylinder.
If the air leaks outward from cylinder connector 1 at this time, it indicates that the shift cylinder leaks. If the air is still exhausted from the exhaust port of the double-h shift valve at this time: it indicates that the double-h shift valve is leaking.
if the transmission has high gear but no low gear, push the gear lever into the low gear area and remove the air inlet connector of the high-speed working cylinder. If there is continuous air leakage from the connector. It means that the shift cylinder leaks.
If the air is still vented from the dual-h shift valve at this time, it indicates that the dual-h shift valve is leaking. Generally speaking, if there is no replaceable seal ring for the fault of double-h shift valve, only the whole valve can be replaced.
If it is judged that it is the fault of high-speed and low-speed shift gas rainbow, generally speaking, it is mainly due to the lax closure of the large and small “O” seal rings on the shift piston.

Postscript:

It is also worth noting that the gearbox has only high gear but no low gear, and the double h shift valve does not show continuous exhaust, so it is generally due to the air leakage of the “O” seal ring of the shift lever. At this time, it can be repaired by replacing the sealing ring.

In short, as long as we understand the structure and working principle of the shift control mechanism, main and auxiliary boxes of Fuller rt11509c transmission and carefully analyze the faults, it is not difficult to find the cause of the fault and there are no difficulties that cannot be eliminated.

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