Synchromesh Gearbox Assembly and
Disassembly Report
1. Name of the Job
Dismantling and Assembling of a Synchromesh Gearbox to Study Its Construction and
Working
2. Objectives
- To gain a deep and practical understanding of the construction, function, and working
mechanism of a synchromesh gearbox used in manual transmission vehicles. - To study and
analyze the arrangement and operation of gears, shafts, and synchronizer assemblies within
the gearbox.
- To identify and understand the functioning of gear selector forks, sleeves, and hubs during
gear shifting.
- To observe the synchronizing action that facilitates smooth engagement of gears without
clashing or grinding.
- To dismantle the gearbox in a methodical manner, inspect the condition of gears and
synchronizers, and reassemble the unit correctly.
- To draw detailed power flow diagrams for all transmission gears including 1st, 2nd, 3rd,
4th, 5th, and reverse.
- To calculate gear ratios by comparing the number of teeth on driving and driven gears
and understand their impact on torque and speed.
- To reinforce the importance of maintenance practices, proper lubrication, and fault
diagnosis in extending the life of transmission systems.
3. Tools and equipment required---
Here are the *tools and equipment used for disassembling and assembling a synchromesh
gearbox*:
1. *Socket and Ratchet Set* – For loosening and tightening bolts and nuts.
2. *Torque Wrench* – To apply accurate torque during reassembly.
3. *Screwdrivers (Flat & Phillips)* – For removing covers, clips, and small parts.
4. *Snap Ring Pliers* – To remove/install snap rings in gear components.
5. *Soft Mallet/Rubber Hammer* – For gentle tapping without damaging parts.
6. *Gear Puller* – To remove gears or bearings from shafts.
7. *Bearing Puller and Installer Set* – For extracting and pressing in bearings.
8. *Feeler Gauge & Vernier Caliper* – For measuring clearances and thickness.
9. *Circlip Plier* – For handling circlips inside the gearbox.
10. *Cleaning Brush and Degreaser* – To clean old oil and grime from parts.
11. *Oil Drain Pan* – To collect used transmission fluid.
12. *Marking Tool* – To mark alignment during disassembly.
13. *Workbench with Vice* – To hold gearbox housing firmly.
4. Observations
- Synchronizers help in smooth and noise-free shifting by equalizing gear speeds.
- Reverse gear uses an idler and is not synchronized, resulting in a typical gear noise.
- Gears slide or are locked using hubs and sleeves depending on the selected gear.
- Gear wear and misalignment can affect shifting performance and gearbox noise.
5. Treatment/Data Collected
- Power flow observed and diagrams drawn for all gears: 1st to 5th and Reverse.
- Gear ratios calculated as follows (example values):
•1st Gear: 3.8:1
•2nd Gear: 2.2:1
•3rd Gear: 1.4:1
•4th Gear: 1:1
•5th Gear: 0.85:1 (Overdrive)
•Reverse: 3.6:1 (using idler gear)
- Components checked for alignment, wear, and lubrication condition.
6. Remarks
- Use proper tools to avoid damage to synchronizer rings and gear teeth.
- Ensure accurate reassembly to maintain gear alignment and smooth operation.
- Replace worn synchronizers, bearings, or seals as needed.
- Lubricate moving parts adequately before final assembly.
- Document gear ratios and verify power flow for correct engagement.
