The bogie is an all-welded, lightweight steel structure with two longitudinal girders and a cross bar. Tractive and braking force transmits from bogie to body via a bogie pin, and 4 steel cables between body and bogie act as lifting supports. While mechanical in nature, this content is genuinely part of AEE's EMU/MEMU knowledge base, since electrical maintenance staff routinely work alongside — and need to understand — the mechanical undergear.
Bogie Frame & Suspension Basics
Axles with self-aligning roller bearings, mounted inside cast steel axle boxes, are rigidly guided by telescopic dashpot and axle box guide assemblies. Helical springs working in parallel with dashpots form the primary suspension. The coach body rests on two side bearers on a floating bogie bolster, which itself rests on air springs supported on a spring plank hung from the bogie frame via swing links — with hydraulic shock absorbers damping the air springs at each end.
Wheel & Axle
| Bogie | New Diameter | Condemning Diameter | Last Shop Issue Size |
|---|---|---|---|
| MC (Motor Coach) | 952mm | 877mm | 885mm |
| TC (Trailer Coach) | 952mm | 857mm | 865mm |
| HCC (High Carrying Capacity) | 952mm | 865mm | 873mm |
- Wheel gauge tolerance: +2/−1mm.
- Permissible tread-diameter variation: 0.5mm within the same axle, 5.0mm within the same bogie, 13.0mm between two bogies under the same coach.
- Material specs: Tyres per IRS R-15/95. Axles per IRS R-16/95 (TC bogies) or IRS R-43/92 (MC & HCC bogies).
Roller Bearings
MC & HCC bogies use direct-mounted, double-row, self-aligning roller bearing No. 22328 C/C3. TC bogies use the slightly smaller No. 22326 C/C3. Under normal service, these bearings need no maintenance beyond inspection and re-lubrication at POH (Periodic Overhaul).
Axle Box Springs & Dashpots
Axle box springs are helical, made from centreless-ground chrome-vanadium/silica-manganese steel, and shot-peened for higher fatigue life — all springs are grouped into 3 categories and used per RDSO Technical Pamphlet No. C-8419 (Rev 1). Dashpots use oil-filled lower spring seats sealed with rubber rings; if the guide-bush surface wears more than 0.4mm or gets scored, the seat must be reclaimed.
Bolster, Side Bearers & Anchor Links
- Side bearers: a hard ground steel plate immersed in an oil bath, with a floating bronze wearing piece. Renew the hard plate when wear exceeds 1.5mm or ridges appear; renew the bronze piece when wear reaches 3mm.
- Oil quantity per side bearer: 2.5 litres (IOC Servoline-68, HPC Yantrol-68, or BPC Bharat Univol-68).
- Anchor links (Trailer bogies only) connect the bolster to the bogie frame diagonally — examine for weld cracks and rubber deterioration in the silent block.
Buffer Height Adjustment
Maximum centre buffer-coupler height from rail level: 1035mm (Motor/Trailer, ICF & BEML), 1064mm (HCC, all makers), 1041mm (Trailer, Jessop). Buffer height lowers over time due to: wheel-tyre wear, side-bearer wear, hanger/hanger-block/pin wear in the secondary suspension, loss of free height in primary/secondary coil springs, and load-deflection characteristics drifting outside prescribed limits.