Mitsubishi FD40-55N Forklift Parts: What Fails on the S6S Class and How to Order Right
The Mitsubishi FD40-55N is the heavy end of Mitsubishi's diesel counterbalance range — a 4.0 to 5.5 tonne truck built around the Mitsubishi S6S six-cylinder diesel, and a close relative of the FD35-50 and FD40K-50K models you'll see on the same yards. These are steel-yard, timber-yard and container-yard machines: they work hard, carry heavy loads all day, and wear their brakes, steering and driveline far faster than a 2-tonne warehouse truck ever will. The good news is that Mitsubishi shared a lot of hardware across this class, so parts are findable — provided you order against the right model code and engine. Read the data plate first, then match the OEM number on the old part. What follows is the FD40-55N by system: the failures that put these trucks in the shop and the parts that put them back to work. Start with the full Mitsubishi forklift parts collection.
The S6S engine: cooling and valve train are where the hours show
The S6S is a durable industrial diesel, but on a heavy truck at high duty cycles the cooling side is what limits its life. If the temperature creeps up under load, check the fan before condemning the radiator — a cracked or distorted blade moves far less air, and the Cooling Fan Blade AG-32B48-00100 covers the S6S on FD35-50 and FD60-70 trucks. Coolant that disappears with no puddle underneath often means a perished bypass hose tucked behind the pump; the Water Pump Bypass Hose 32A46-00900 spans a wide slice of the S4S/S6S range including FD40K-45K, FD45-50 and FD50K. Higher up, smoke on start-up, low compression or noisy valve gear means a top-end refresh — the Valve Guide 32A01-01600 and Valve Spring Retainer 30604-31601 fit the S4S and S6S families and are the usual wear items in that job. See more engine parts and cooling parts.
Brakes: the system that decides whether a 5-tonne truck stops
Brake wear scales with load, and on a 4–5.5 tonne machine the shoes go quicker than most owners expect. A long pedal, a truck that pulls to one side, or a grinding noise on the way down a ramp all point the same way. The Brake Shoes C-K2-13207-73015 cover the Mitsubishi FD35-50 and FD35-50K, while the Brake Shoes 91846-17200 fit the FD35-50 and FD40K-50K. Don't defer this one — on a loaded heavy truck, worn shoes are the difference between stopping and not. Browse all forklift brake parts.
Steering: play and wander on a hard-working steer axle
Heavy trucks put enormous side load through the steer axle, so free play at the wheel, a clunk on lock, or a machine that wanders on a straight run are common at high hours. The Tie Rod End 31230-02540 (FD40-50K / FD40-50KL, left-hand) takes up slack in the linkage, and the Rear Axle Hub Cap 91843-00900 (FD35-50) seals the hub so grease stays in and grit stays out. Inspect the steer axle at every service — a little play now is a wheel bearing later. See steering parts.
Mast, transmission and hydraulics: lifting five tonnes, repeatedly
Forks that settle under load, a mast that judders, or a truck that won't hold a ramp are the three complaints that dominate this class. Worn load rollers cause the judder — the Mast Roller 94447-11300 is listed for the FD/FG40-55N and FBC35-55N. In the driveline, a transmission that slips or shifts harshly is usually the clutch pack: the Clutch Separator Plate 93724-02600 (FD40-55N, FD40-55CN, FD100-160N) and the Friction Plate 3EC-15-31270 (FD40-160N, FD50K) are the wear parts inside. If lifting is simply slow and weak everywhere with clean oil and good seals, the pump is tired — the Hydraulic Pump 91871-14200 (FD40K/KL-50K/KL, S6S) and the Oil Pump Drive Assembly 91871-30040 (FD35-50, F19B/S6S) restore full flow. See mast parts, transmission parts and hydraulic parts.
Electrical: small faults, big downtime
On older heavy trucks a surprising share of “won't start” and “dead circuit” calls come down to a tired relay rather than anything expensive. The Relay 91A05-01600 covers the whole FD10N-55N range and is worth keeping on the shelf. Browse electrical parts.
Reading your Mitsubishi: model code, chassis prefix and engine
Mitsubishi's codes look cryptic but carry everything you need. “FD” is diesel (FG is LPG/gas), the number is capacity (FD45 = 4.5 t), and the trailing letter identifies the series — “N” trucks are the later generation. Just as important is the chassis/engine prefix you'll see in fitment lists (F19B, F19C, F28A, F28B, CF19D and so on): that code, not just the capacity, decides which brake, steering and hydraulic parts fit. Find the data plate on the cowl or near the operator's seat and note the full model, the chassis prefix and the serial. Then confirm the engine — most of this class is the S6S, but the S4S appears lower down the range and shares many top-end parts. With model, prefix and engine in hand, search by the OEM number stamped on the old part; Mitsubishi numbers usually look like 91xxx-xxxxx or 32Axx-xxxxx. If you only have the model, search that plus the component and check the application list before you buy.
A maintenance rhythm that suits a hard-working heavy truck
This class rewards a tighter routine than a light warehouse machine. Check oil, coolant and hydraulic level daily and look underneath for fresh drips. Inspect brake shoes and the steer axle at every service rather than every other one — load accelerates both. Keep the radiator core and fan clear of debris, because cooling is the first thing to suffer in a dusty yard. And watch fluid cleanliness: heavy trucks generate more heat and more wear metal, so clean hydraulic and transmission oil pays for itself in pump and clutch-pack life.
Frequently Asked Questions
Do FD40-55N parts interchange with FD35-50 or FD40K-50K?
Many do — you'll often see all three in the same fitment list, especially for brakes, clutch packs and pumps. But the chassis prefix (F19B, F19C, F28A…) is what decides it, so check the application list rather than assuming.
Which engine is in my truck?
The FD40-55N class is normally the Mitsubishi S6S six-cylinder; smaller trucks in the family use the S4S. Read the tag on the block — engine, cooling and top-end parts are chosen by engine, not by capacity.
What does the “N” at the end of the model mean?
It identifies the series/generation. Always quote it (FD45N, not just FD45) because parts changed between generations.
Is it worth rebuilding the transmission rather than replacing it?
On this class, usually yes. Clutch separator and friction plates are a fraction of the cost of an assembly, and a slipping transmission caught early rarely needs more.
Can't find the right part? Send us a part request with your model, chassis prefix and engine, and we'll look it up.
