Automatic transmission hydraulic control valve body failure should be how to overhaul
The automatic transmission's electronic control system, hydraulic system, and mechanical components are closely interconnected. The hydraulic system, particularly the oil control valve body, is highly complex—its internal oil channels resemble a maze or a printed circuit board. Components such as plungers of various sizes, springs of different thicknesses, ball valves, plastic balls, filter seats, stop bits, accumulators, and more make up the valve body. Each part’s orientation, position, and dimensions are crucial, making the assembly appear intricate and overwhelming. Repairing the valve body requires detailed information, thorough understanding, and careful handling.
For an automatic transmission (AT) gearbox, disassembly and overhaul of the valve body are typically considered only when the friction plates are severely burned, the planetary gears are worn, or the vehicle has reached about one-quarter of its expected mileage with heavily contaminated ATF fluid. In electronically controlled hydraulic automatic transmissions, most valve body failures result from internal dirt or clogging due to debris in the oil. Disassembling and overhauling the valve body is a critical step in the repair process.
Before removing the valve body from the transmission case, it's essential to carefully disconnect the flat wire from the external solenoid valve. Since these wires are made of plastic and have been submerged in ATF oil for a long time, they can become brittle under high temperatures. Use a custom-made tool to gently push the plug down and remove it in that direction. Be cautious of small parts that might fall off, and remember their original positions. Soak the valve body in kerosene for a while before cleaning it thoroughly.
Place the valve body on a clean workbench and remove the screws connecting the upper and lower sections. Hold the upper body and middle bulkhead firmly, then flip the partition so the one-way ball doesn't fall out. Carefully separate the components for further inspection. After removing the bulkhead, before taking out the control valve plungers, use the residual oil on the bulkhead to trace the hydraulic layout onto a thick white cardboard. Mark each part clearly on the diagram for reference during reassembly.
Soak the valve body in clean kerosene or use a carburetor cleaner with a small brush to remove deposits. If necessary, gently scrub with a nylon cloth. Visually inspect the valve body for cracks, deformations, and ensure all plungers move smoothly with a small screwdriver. Check that the piston surfaces are free of damage. Dry the valve body and apply a small amount of automatic transmission fluid to the oil ports before placing the cleaned parts back inside. Ensure all components are present and in good condition.
Check if any plungers are stuck. Most plungers have a limit device at the outer end, such as a cylindrical stopper, pin, or cotter pin. When removing them, hold the plunger in place with your finger or a screwdriver to prevent the spring from popping out. If a plunger is jammed, gently tap the body with a wooden or rubber hammer to loosen it. For stubborn cases, use 1200-grit sandpaper soaked in ATF oil to polish the plunger along the arc, but avoid polishing the valve hole itself. A clean plunger should slide freely under its own weight. It's best to overhaul and reassemble one group of plungers at a time to avoid misalignment.
Inspect the springs’ free length and diameter against the specifications in the service manual. Replace any worn or damaged springs. Missing one-way ball valves can cause severe shifting shocks, and incorrectly installed throttle valve damping blocks may lead to improper gear shifts. Pay close attention to the positions of all parts—front, back, left, and right. Even a small mistake can render the valve body non-functional.
When replacing the valve body’s sealing rings, ensure that the following areas are fully inspected and replaced: the piston seal, the accumulator piston seal, the control valve seal, and the seals on both sides of the clutch support oil inlet. Check for cracks or wear on the accumulator piston and replace the piston ring if needed. These steps are crucial, as poor sealing can lead to overheating and premature friction plate failure. Typically, after 3,000 km, the force device may start to degrade, and this is directly related to the four sealing areas mentioned above.
Clean and dry the separator, checking for deformation and ensuring oil holes are smooth and leak-free. Make sure the old and new gaskets and diaphragms fit properly. Verify that the paper gasket aligns correctly with the oil flow paths—a critical detail. Soak the new seals in ATF oil for a few minutes before installation. Place the valve body components flat, not upright, to avoid damage. Reassemble the upper and lower sections, the middle bulkhead, and evenly tighten the connecting screws (note the screw lengths to avoid misinstallation). Tightening torque is generally between 5-10 Nm, depending on the model. For example, Volkswagen valve body bolts require 5 Nm; too much or too little torque can affect hydraulic pressure. Once assembled, the valve body is ready for installation.
Hydraulic Hose Joint,Orfs Coupling For Hoses,Hose Adaptor,Carbon Steel Pipe Expansion Joint
JiangSu Speeder heavy machinery Co., LTD , https://www.speederjoint.com