1939–1953 · the first hydraulic Bedfords · 3,519cc six · and the K that is not a TK
The 1939 redesign is where Bedford brakes stop being rods and start being hydraulics. Nothing crosses that line.
In mid-1939 Bedford replaced the whole W-series range at once, and the new line-up is the one that matters here: K at 30–40cwt, MS and ML at 2–3 ton, OS and OL at 3–4 ton, OS/40 and OL/40 at 5 ton, and the OB bus. Every one of them is Lockheed hydraulic with Clayton Dewandre vacuum assistance on all four wheels — where the W-series it replaced was rod-operated with a Dewandre vacuum servo. That is the single most useful fact about a pre-war or early post-war Bedford, and it is worth establishing before anything else: a W and an O of the same size share no brake hydraulics, because the W has none. Underneath, the common thread is the 3,519cc (214 cubic inch) overhead-valve six at 72bhp at 3,000rpm, bore and stroke 85.72 × 101.6mm, firing order 1-5-3-6-2-4, four-speed box and a fully floating rear axle.
The same engine and the same brakes went to war. The military versions of the O were redesignated OX (24,429 built) and OY (72,385) — OYD general service, OYC water and petrol tanker, OXA the armoured anti-tank home-defence body. Alongside them ran the MW 15cwt, 65,995 built from 1939 to 1945, and the QL 4×4, “Queen Lizzie”, in service from March 1941 with 52,247 built. The OB bus is the famous one, usually wearing a Duple Vista body of ash framed with steel on a hardwood floor, 29 seats and that bullnose front — and it is worth correcting a common claim, because only 73 OB chassis were built before the war stopped production. The real run is October 1945 to November 1950, 12,693 chassis; the wartime austerity bus is the OWB, a different vehicle with cast iron in place of alloy and wooden slat seats. After 1953 the normal-control truck became the TA / A type, about 200,000 of them, and its sixes are Chevrolet-derived Stovebolt developments, with Perkins diesels optional.
Bedford K, M & O Types — specification & changes within the model
- Brakes
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Lockheed hydraulic, Clayton Dewandre vacuum assisted, all four wheels, on the K, M, O, OB and the military OX, OY, MW and QL. The W-series before them is rod-operated with a Dewandre vacuum servo. 1939 is the line and nothing crosses it.
- Engine
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3,519cc (214 cu in) overhead-valve six, 72bhp at 3,000rpm. Bore × stroke 85.72 × 101.6mm, firing order 1-5-3-6-2-4, four-speed, fully floating rear axle. The same unit runs the OY, OX, MW, QL and the OB bus.
- The K that is not a TK — read this before ordering
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In Australia the Bedford TK was marketed as the “K Series”, and GM-H issued a Bedford K Series Motor Trucks booklet in February 1965. That is a completely different truck from the 1939–53 K type on this page — forward control, twenty years later, different everything. If your paperwork says “K Series” and the cab sits over the engine, you have a TK. Ask us and we will sort it out.
- The OB — and a date that is usually printed wrong
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Only 73 chassis were built before the war stopped production. The real run is October 1945 to November 1950, 12,693 chassis. “Built 1939 to 1951” is wrong. The wartime bus is the OWB, 3,398 built, with cast iron substitutions and wooden slat seating for 32 — a different vehicle.
- Military numbers
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OY 72,385 · OX 24,429 · MW 65,995 · QL 52,247. The QL variants: QLD cargo, QLB Bofors tractor about 5,500, QLR signals with an auxiliary generator, QLT troop carrier 3,300 or more from August 1941, QLC and QLW tipper.
- What came next
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TA / A type, 1953–58, about 200,000 built, renamed TD on a 1957 update and then TJ from 1958. Its sixes are Chevrolet-derived, with Perkins fours and sixes optional. The heavy end was the S type “Big Bedford”, 1950–59, on the 4.92-litre 300 cu in petrol six at 110bhp.
- Not claimed
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Electrical voltage and earth polarity. One source says the MW was 12 volt “upgraded from 6 volt in earlier iterations” without naming a model or a date, which is not a usable fact. No chassis-number breakpoint exists for any Bedford change, anywhere — every change is dated only. Check the vehicle.
