When your gearbox starts acting up, it’s crucial to take action quickly to prevent further damage. While the process may seem daunting, with the right tools and knowledge, you can tackle this repair like a pro.
We’ll guide you through each step, from the initial assessment to the final adjustments, so you can get your gearbox running smoothly again.
Can a Gearbox Be Repaired
Yes, a gearbox can often be repaired. Common repairs include replacing worn gears, bearings, or seals. However, the cost-effectiveness of repairing versus replacing the gearbox depends on factors like the severity of damage, gearbox type, and vehicle make/model.
How to Rebuild a Gearbox: Step by Step
Step 1: Disassemble the Gearbox
Start by draining the oil and removing any external accessories such as the speed sensor or shifter assembly. Next, unbolt the gearbox casing and carefully split it apart. Take care not to damage the mating surfaces.
With the casing open, remove the input and output shafts along with any bearings, snap rings, or spacers. Make note of the order and orientation of these parts for reassembly later. Finally, lift out the gears and lay them out in the order they were installed. Inspect each component for wear, cracks, pitting or other damage.
Step 2: Clean and Inspect Components
With the gearbox fully disassembled, clean each part thoroughly with a degreasing solvent. Use a stiff brush to remove any caked on debris or residue. Dry the parts completely with compressed air.
Once clean, carefully inspect every component again looking for signs of excessive wear or damage that would necessitate replacement:
- Gears: Check for chipped, cracked or missing teeth. Also look for signs of overheating such as discoloration or material transfer.
- Bearings: Rotate bearings slowly feeling for roughness, pitting or flat spots. Also check that they spin freely with no binding or excessive play.
- Shafts: Look for scoring, grooving or twisting of the shafts. Use a micrometer to measure the shaft diameters to check for excessive wear.
- Synchronizers: Inspect synchronizer friction surfaces for signs of glazing, heat damage or uneven wear. Measure clearances against spec.
- Casing: Check casing and covers for cracks, stripped threads or damaged mating surfaces. Verify the casing is not warped.
Replace any components that are excessively worn or damaged. If in doubt, it is always best to replace with new parts during a rebuild.
Step 3: Install New Bearings and Seals
Assuming the shafts and housing are reusable, install new bearings and oil seals on the input shaft, output shaft and countershaft. Coat the outside diameter of the bearings with gear oil before installation to aid assembly.
For press-fit bearings:
- Place the shaft in a hydraulic press with support blocks that clear the bearing shoulders.
- Lubricate the bearing bores and align the new bearing squarely on the shaft.
- Slowly press the bearing until it seats firmly against the shaft shoulder. Do not apply force to the inner bearing race.
For slip-fit bearings, apply gear oil to the bore and slide the bearing into place by hand. Secure non-locating bearings with the proper size snap rings. Oil seals should be lightly coated on the outside with RTV sealant and pressed squarely into the casing or cover until flush.
Step 4: Reassemble Gears and Shafts
Lubricate the bearing journals on the gearbox shafts with assembly oil. Then begin sliding the gears and synchronizers back onto the shafts in the reverse order they were removed. Make sure to include any thrust washers, spacers or snap rings in their proper locations.
Mesh the gears on their respective shafts and carefully lower the assembly into the gearbox casing. Make sure the shift forks engage correctly with the synchronizer sleeves. Check that the gears rotate smoothly with no binding.
Once the gear assembly is in place, install the front and rear gearbox covers along with any dowels, gaskets or sealant as required. Secure the covers evenly in a criss-cross pattern with the proper bolt torque.
Step 5: Fill with Oil and Test
With the gearbox reassembled, fill it with the manufacturer’s recommended type and quantity of gear oil. Spin the input shaft by hand to distribute oil to all the components.
Finally, test the rebuilt gearbox before putting it into service. With the gearbox properly mounted, run it through all the gear ranges and check for smooth shifting, proper oil circulation and any unusual noises. Check for oil leaks from the seals or gaskets. Road test the vehicle and verify proper operation under load.
FAQs
Is an automatic gearbox repairable
Yes, automatic gearboxes are repairable. Common issues include worn clutches, solenoids, and sensors. Repairs typically involve replacing damaged components or rebuilding the transmission.
Is it worth fixing a gearbox
Fixing a gearbox is often worth it if the repair cost is less than the vehicle’s value and a replacement is too expensive.
Difficulty of fixing a gearbox at home
Fixing a gearbox at home is very difficult. It requires specialized tools, knowledge, and a clean workspace. Most people should have a professional repair their gearbox.
How much does it cost to fix a gearbox
Gearbox fix costs vary widely depending on the issue and vehicle make/model. Minor repairs start around $500, while a complete rebuild can cost $2000-$4000+.
