Gino 1 Seibi › Chassis and brake topics

Chassis and brake topics for the SSW (i) maintenance exam

The chassis (シャシ) is the second official scope area. It covers jobs a mechanic does every day: replacing brake pads, rotating tyres and tightening wheel nuts. This page sums up what each unit does and what to watch while working on it.

Last updated: 2026-10-10

At a glance

Clutchconnects and cuts engine power
Differentiallets wheels turn at different speeds
2 typesof brake: disc and drum
Crosswiseorder for wheel nuts

Power train

Engine power passes through the clutch (クラッチ), transmission (トランスミッション), propeller or drive shafts (ドライブ・シャフト) and differential (ディファレンシャル) to the wheels.

The clutch connects and cuts engine power for smooth starts and gear changes. The pressure plate presses the clutch disc against the flywheel; pressing the pedal releases that pressure.
The transmission changes the gear ratio, giving strong pulling power when starting and high speed when cruising, and lets the car reverse.
The differential lets the left and right wheels turn at different speeds in a corner, because the outer wheel travels farther.

Brakes

Type	How it works	What to check
Disc brake (ディスク・ブレーキ)	Pads clamp both faces of a rotating disc	Pad thickness, disc runout and wear, caliper leaks
Drum brake (ドラム・ブレーキ)	Shoes press against the inside of the drum	Lining thickness, drum inner diameter, wheel cylinder

Brake fluid (ブレーキ液) absorbs moisture from the air. Fluid with water in it boils at a lower temperature, so hot brakes can form vapour bubbles (ベーパ・ロック) and the pedal goes soft. That is why the fluid is replaced regularly, different types are never mixed and the reservoir stays closed. Air in the lines must be bled out (エア抜き).

Steering and suspension

The steering system turns the rotation of the steering wheel into steering movement of the front wheels. Toe-in (トーイン) means that, seen from above, the front edges of the front wheels are slightly closer together than the rear edges; a wrong setting wears tyres unevenly. Springs carry the body and absorb shocks from the road, while shock absorbers (ショック・アブソーバ) quickly damp the spring's oscillation.

Wheels and tyres

Check tyre pressure when the tyres are cold, against the vehicle's specified value.
Check tread depth; tyres have wear indicators (スリップ・サイン). When the tread wears down to them, replace the tyre.
Fitting a wheel: snug the nuts in a crosswise order, lower the car, then tighten to the specified torque with a torque wrench (トルク・レンチ), again crosswise. Going round in a circle can seat the wheel off-centre.

Chassis ○× items often swap two units: the job of the spring and the shock absorber, of disc and drum brakes, of the clutch and the transmission. Knowing which part does what clears most of them.

Sources checked: the JASPA specified skills test page (2024 test summary), the MLIT implementation rules and acceptance handbook (MLIT page) and the Prometric booking page. Rules can change, so check the latest version at these sources.

FAQ

What does the differential do?

It lets the left and right wheels turn at different speeds in a corner, because the outer wheel travels farther.

Why is brake fluid replaced regularly?

Brake fluid absorbs moisture. Water lowers its boiling point, so hot brakes can form vapour bubbles (vapour lock) and lose braking power.

How do I tighten wheel nuts correctly?

Snug them a little at a time in a crosswise order, then tighten to the specified torque with a torque wrench, again crosswise.

How do disc and drum brakes differ?

Disc brakes clamp pads onto a rotating disc. Drum brakes press shoes against the inside of a rotating drum.

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