This is a guide on how to rebuild a transmission.
Essential Preparation and Transmission Removal
The rebuild process requires a meticulous approach to preparation and workspace organization. A clean, well-lit work area is necessary to prevent contamination of internal components. Specialized tools are required, including a transmission jack, a torque wrench for accurate assembly, and dial indicators for measuring clearances. Follow safety protocols by disconnecting the vehicle’s battery and raising the vehicle with sturdy jack stands.
Before unbolting the unit, completely drain the transmission fluid, and carefully disconnect any cooler lines or electrical connectors. Remove the driveshaft or drive axles next, followed by any exhaust components that obstruct access to the bell housing bolts. Position a transmission jack to support the unit’s weight, allowing for the removal of the crossmember and transmission mounts.
With the transmission supported, remove the bell housing bolts connecting it to the engine, often requiring a long extension to reach upper fasteners. Automatic transmissions require the removal of the torque converter bolts through an inspection plate, allowing the converter to separate from the engine’s flexplate. Once all attachments are released, carefully lower the transmission with the jack and move it to the workbench.
Detailed Disassembly and Component Diagnosis
Disassembly starts on a dedicated bench, where cleanliness is paramount. As components are removed, document their exact order, orientation, and location, often using photographs, to ensure correct reassembly. Separate the case halves, then systematically remove internal assemblies like the valve body, gear sets, drums, and shafts. Every component is then subjected to a thorough cleaning process using solvents to remove all debris and residue.
Diagnosis of wear and damage determines what needs replacement. Inspect hard parts, such as shafts and planetary gear sets, for cracks, pitting, or excessive wear on the splines and gear teeth. For automatic transmissions, check the clutch packs and bands for signs of burning or glazing, which indicates heat damage. Worn friction plates and bands must be replaced.
Inspection of Manual Components
In manual transmissions, inspect the synchronizer assemblies for wear, often indicated by excessive gear grinding before disassembly. Check the brass rings for damage or excessive clearance.
Inspection of Automatic Components
The valve body is carefully disassembled. Inspect its internal bores, valves, and springs for scoring or sticking that could cause pressure issues.
Component Selection
Measuring critical clearances and thicknesses, such as friction plate thickness and spacing between hard parts, against factory specifications is necessary. Replacement parts are typically sourced from a master rebuild kit.
Precision Reassembly Procedures
Reassembly requires precision, using the new seals, gaskets, and friction components from the rebuild kit. Carefully install new seals and gaskets throughout the case and internal components to ensure proper hydraulic sealing and prevent fluid leaks. Apply lubrication to all rotating and sliding parts during assembly, often using petroleum jelly to hold thrust washers and bearings in place temporarily.
Setting the internal clearances is the most technical aspect, influencing performance and longevity. Clutch pack clearance is set by selecting snap rings or shims to achieve the manufacturer’s specified tolerance. If the clearance is too loose, the shift will be delayed; if too tight, the clutches can drag and burn.
Input shaft end play, the axial movement of the main shaft, is set using selective washers or shims to accommodate thermal expansion. Stack the internal assemblies in the correct order, ensuring splines align and thrust surfaces are seated. Reinstall the valve body, ensuring all check balls and valves are correctly positioned. Finally, close the case halves and tighten all bolts in a specific sequence to the exact torque specifications.
Installation and Initial Testing
Once the case is sealed, carefully lift and position the rebuilt transmission back into the vehicle using the transmission jack. Reinstallation involves aligning the bell housing with the engine block, ensuring the automatic transmission’s torque converter is fully seated before bolting the case. Reattach all external connections, including the driveshaft, electrical connectors, vacuum lines, and shifter linkages, in reverse order of removal.
Refill the transmission with the correct type and quantity of fluid specified by the manufacturer, as incorrect fluid can compromise the new friction materials and seals. Once the vehicle is running, conduct initial checks while stationary, cycling through all gear ranges to confirm proper engagement. Perform a thorough leak check, paying close attention to the newly sealed pan gasket and output shaft seals.
The final step involves a controlled road test to assess the unit’s operational performance under load. During this test, monitor for smooth, timely shifts, the absence of unusual noises, and correct engagement in all gears. A short break-in period, typically around 500 miles, is recommended for the new friction materials to properly seat, during which time excessive load or aggressive driving should be avoided.