DB MkIII

DB MkIII Description

In production: March 1957—July 1959

Chassis numbers: AM300/3A/1300—AM300/3/1850

The final development of the cars based on Claude Hill’s chassis (and therefore the "Atom" saloon) and the Lagonda six-cylinder twin overhead camshaft engine is the DB Mark III, also known as the DB2/4 Mark III, but, please, not Mark 3. (The description of this car as the DB3, a common practice in the second-hand car trade, is entirely misleading. No punishment is too severe for a Member of the Club guilty of this dreadful solecism). The Mark III was launched at the Geneva Show in March 1957 and was available only for export until it was shown at the London Motor Show in October. It remained in production for about eight or nine months after the DB4 had been introduced. Some 310 cars were exported to the U.S.A.

The prototype, AM300/3A/1300 (DP 193), had disc brakes on all four wheels, but the following 100 cars were offered with discs on the front wheels (as fitted experimentally on LML/855 in 1956) as an optional alternative. These were Mark IIIAs, although only about eight were so designated (e.g. by /3A/ in the chassis number): only the first (AM300/3A/1301) had right-hand drive, most going to the U.S.A. Two of them (/1317 and /1346) were prepared for racing, owned by Elisha Walker and Joe Lubin respectively. In other respects the chassis of the Mark III is the same as on the Mark II.

From chassis 1401, the Girling front discs became standard, known as the IIIB specification at the Works; although only the first, 1401 (MP 197P) is AM300/3B/, at least one other (AM300/3/1406) is described as a Mark IIIB on the chassis plate. Racing the DB3S had hastened development of the VB6J 3 litre engine, so that much had been learned, particularly weaknesses. So the DBA engine had many new features as a result of Tadek Marek's re-designed of it.

The standard DBA version of this engine (DP 164) had a stiffer crankcase, a new block (with top seating liners), new crankshaft, oil pump and timing chain, new exhaust and induction manifolds, the ports were based on the DB3S engine, larger valves, high lift camshafts (after the first 150) and 14 mm. plugs. With the same capacity (2,922 c.c.), twin SU carburettors and compression ratio (8.16:1) as the VB6J engine, the improved breathing provided an output claimed to be 162 b.h.p. at 5,500 r.p.m.

Twin exhausts were an optional extra, said to add 16 b.h.p.

In 1958 a special series engine (DBB/) rated at 195 b.h.p., with three Weber 35 DCO twin-choke (or three SU HV6) carburettors, higher compression ratios (8.6:1), special camshafts and twin exhausts as standard, was offered as an optional extra. Ten cars were fitted with this engine.

At the 1958 London Motor Show a new special series engine, the DBD version, similar to the DBB but with three (sometimes only two) SU HV6 semi-downdraught carburettors, was offered. The power output of the DBD engine was quoted as 180 b.h.p.: it was fitted to 47 cars. A special competition engine, DBC, has been mentioned in earlier Registers: this is probably the three Weber (45 DCO) version with an output of 214 b.h.p. included in a January 1959 price list, with among other modifications, special connecting rods, high compression pistons and racing camshafts. It was recorded as fitted to only one car (AM300/3/1708, delivered in Havana in October 1958).

The main change in the appearance of the car was the adoption of the elegantly shaped radiator opening found on the DB3S which gave the Mk III a more modern appearance and yet retained the essential features of the radiators of the past and the consequent compound curves of the front of the bonnet, can be traced, in one form or another, on all subsequent models up to and including the last of the V8 series (Virage etc.), on into the V12 series of cars an the V8 Vantage of 2005. The higher roof was not so obvious as on the Mark II, as the chrome strip was omitted: chrome beading in the windscreen surround distinguished it from the original model of 1953. The rear body was similar to the Mark II even to the retention of the small rear lights on a few early cars, though in due course a lamp cluster from the contemporary Humber Hawk gave the rear a cleaner appearance. Opening rear quarter lights (rear side windows) were fitted.

The Mark III was nearly 9 in. (23 cm.) longer than the DB2 and weighed about 350 lb (159 kg) more, an increase of about 15 per cent, but more than an extra 50 per cent power was available from the standard DBA, compared with the original LB6B.

Inside, the main difference was a completely different facia and instrument panel (which remained in use until the DB6 Mark II was dropped in 1970).

There were 84 Drophead Coupés and, near the end of the run, 5 Fixedhead Coupés with DBD engines. The standard transmission was the same as on the Mark II. Optional extras included overdrive (on the III B). The clutch was hydraulically operated for the first time.

For 1959, also for the first time, automatic transmission (Borg Warner) was offered (as an extra) for a production Aston Martin: it was installed only in cars with the DBA engine, four drophead coupés and one saloon. A brake vacuum servo was included in the system, reducing pedal pressure.

The Mark III was described in The Motor (October 2nd 1957) and The Autocar (October 4th 1957) and was road tested by Sports Cars Illustrated (October 1957), Autocar (AM300/3B/1401, December 27th 1957), Road and Track (December, 1958) and Autocourse and Sporting Motorist (Jan. 1959).

DB MkIII Derivatives

Saloon

The final development of the Claude Hill chassis (as first seen in the Atom) appeared in the form of the Mark III (the 2/4 bit was dropped). The most noticeable change was the adoption of a DB3S style grille and a revised instrument binnacle (which echoed the style of the grille). The Mark III was also the first Aston Martin to be available with front disc brakes as standard during the production run. Also the engine had been substantially redesigned by Tadek Marek before he started work on the DB4 engine.

The standard 3 litre (2922cc, twin SU carbs) engine fitted to the Mark III was designated as the DBA version and produced 162 bhp @5500 rpm although with the fitting of optional twin exhausts, this could be raised to possibly 178 bhp. A special series engine using three twin choke Webers, twin exhausts and special camshafts, called the DBB version was able to produce 195 bhp. Just to add more choice, a DBD version was also available with three SU carbs and producing 180 bhp.

Drophead Coupe

The elegant Drophead Coupe Mark III was offered alongside the regular saloon. It was the final example of a convertible in the Feltham line of cars although coachwork was by Tickfords in Newport Pagnell. In 1959 the drop head was deleted from the range and it would be more than two years before Aston Martin offered a soft top car in the form of the DB4 convertible.

During the two year production run of the Mark III, 551 examples of all deriratives were built, yet only 84 were dropheads. A majority of these drop heads were built with the standard fit 3 litre DBA engine with twin SU carburettors offering 162 bhp. Fourteen cars had the more powerful DBD triple SU carburettor unit with 180 bhp, and just two had the most powerful DBB special series engine (195bhp) with triple Webers instead of the SU’s. Thus the DB Mark III drophead coupes with either the DBD or DBB engines are amongst the most desirable of the Feltham era cars.

Fixedhead Coupe

One of the rarest road cars produced by Aston Martin was the DB Mark III Fixed Head Coupe. Built towards the end of Mark III production, all were fitted with the DBD special series engine delivering 180 bhp. In total, only five of these cars were ever built.

DB MkIII Specification

Standard DBA 3 litre engine
Twin overhead camshafts
Hemispherical combustion chambers
Bore 83 mm, stroke of 90 mm, capacity of 2,922 c.c.
Compression ratio 8.16:1 DBB/ 8.6:1;
Valve clearances Inlet 0.011" - 0.013" Exhaust 0.012" – 0.014" Cold. Eng 1075 onwards Inlet & Exhaust 0.00 9" to 0.011".
Valve timing engines up to 1073: Inlet camshaft; Set No 1 piston to TDC firing stroke. Turn crankshaft 10° after TDC. Turn camshaft until inlet valve no 1 cylinder is open 0.082" – 0.087" on opening side. Bolt up sprocket. Exhaust camshaft; Set No 1 piston to TDC on firing stroke. Turn crankshaft 10° before TDC. Turn camshaft until exhaust valve no 1 cylinder is open 0.082" – 0.087" on closing side. Bolt up sprocket
Valve timing engines 1074 onwards: Inlet camshaft; Set No 1 piston to TDC firing stroke. Turn crankshaft 10° after TDC. Turn camshaft until inlet valve no 1 cylinder is open 0.089" – 0.091" on opening side. Bolt up sprocket. Exhaust camshaft; Set No 1 piston to TDC on firing stroke. Turn crankshaft 10° before TDC. Turn camshaft until exhaust valve no 1 cylinder is open 0.089" – 0.091" on closing side. Bolt up sprocket
Fuel System
DBA/ had 2, H6 (1¾") carburettors, SV needle. Supplied by two SU electric pumps.
DBB/ and DBD/; Three Weber 35 DCO twin-choke (or three SU HV6)
Ignition System
12 volt coil and engine driven Lucas distributor.
KLG 14mm F 100 spark plugs.
Contact breaker gap 0.012"
Static ignition timing 10° before TDC.
Electrical System
12 volt system and dynamo.
Transmission
David Brown gearbox
Optional Laycock De Normanville overdrive
Hydraulically operated Borg and Beck 9" single dry plate clutch.
Alternative final drive ratios; 3.27:1, 3.5:1 or 4.09:1:1 (recommended for cars fitted with overdrive).,
With 3.77:1 axle ratio, overall ratios were:
Gearbox Overall Close ratio
Overdrive 2.93:1
4th 1:1 3.77:1
3rd 1.33:1 5.01:1 1.26:1
2nd 1.98:1 7.46:1 1.26:1
1st and reverse 2.92:1 11.0:1
Steering
Marles worm and roller with a divided track rod.
Brakes
The lining area when four Wellworthy Ltd. light alloy 'Al-Fin' drums were used was 168.4 sq. in.
With front disc brakes, total lining area was 111 sq. in.
Suspension
Front: Trailing link with coil springs and Armstrong lever dampers.
Rear: Live Salisbury axle located by trailing links and transvers Panhard rod.
Body
An aluminium skin over a frame of steel tubes, steel sill and wood fillets.
The bonnet and wings were a single unit, hinged at the front, lifting to gain access to the engine.
Interior
Leather covered bucket seats with tilting squabs to allow access to the small rear seats.
All trim panels were carpeted or leather covered.
The back panel for the rear seats folded forward to extend the rear luggage space.
Opening rear window.
An interior heater was a 'standard' fitment.
Wheels and Tyres
16" wire, splined knock-off with 600 x 16 Dunlop or Avon tyres.
Main dimensions
Length 14' 3½" (435.5 cm.)
Height 4' 6¼" (138 cm.)
Width 5' 5" (165 cm.)
Clearance 5 ¾" (15 cm.)
Track 4' 6" (137 cm.)
Wheelbase 8' 3" (251.5cm.)
Turning circle 35' (1,067 cm.)
Dry weight 2,800 lb. (1,270 kg.)
Fuel System
Capacity 17 gall. (77.2 litre), of which 3 gall. (13.6 litre) was in reserve.
Fuel Type Petrol 95 Ron, leaded.
Maximum power
DBA 162 b.h.p. at 5500 r.p.m with single exhaust. 178 b.h.p. with twin exhaust system.
DBB/ 195 b.h.p., (twin exhausts as standard).
DBD version (similar to the DBB) 180 b.h.p.
DBC version 214 b.h.p.
Maximum torque
DBA, 178 lbs/ft at 3100 RPM.
Acceleration
The Autocar recorded 0-60 m.p.h. 9.3secs, 0-100 m.p.h. 31.0secs.and a standing ¼ mile 17.4 seconds Maximum speed of 120 m.p.h. Roy Salvadori in Autocourse and Sporting Motorist recorded a 0-60 time of 8.2 secs and 0-100 in 23.8secs 0 to 60mph; Autocourse 10sec; Autosport 10 secs.
Maximum speed
Autocourse 119.2 mph; Autosport 118.4 mph.
Prices (Prices in brackets include U.K. purchase tax)
1957 1958 (Oct) 1959 (Jan)
Mark III Saloon £2,050 (£3,076) £2,050 (£3,076) £2,050 (£3,076)
Mark III Drophead Coupé £2,300 (£3,451) £2,300 (£3,451) £2,300 (£3,451)
Mark III Fixed Head Coupé £2,300 (£3,451)
Optional extras:
Whitewall tyres £7 10s (£11) £10 (£15)
Twin exhaust £36 (£54) £36 (£54)
Oil Cooler £50 (£75) £50 (£75)
Radio (HMV) £43 (£65) £43 (£65)
Three-eared hub caps £5 (£7 10s) £5 (£7 10s)
Chrome Wheels £45 (£67 10s) £45 (£67 10s)
Wood rimmed steering wheel £15 (£22 10s) £15 (£22 10s)
Close ratio box £10 (£15) £10 (£15)
Alternative back axle £10 (£15) £10 (£15)
Overdrive £70 (£105) £70 (£105)
Borg Warner transmission £150 (£225)
Competition clutch £18 (£27) £18(£27)
Competition shock absorbers £5 (£7 10s) £5 (£7 10s)
28gall.(127.3litre,33.6USgall.) tank £80 (£120) £80 (£120)
Wing mirrors, each £1 15s (£2 10s) £1 15s (£2 10s)
Fog and spot lamps, each £6 10s (£10) £6 10s (£10)
Day/night mirror £2 10s (£4) £2 10s (£4)
Special series engine (DBD) £70 (£105)
Special competion engine (DBC) £350 (£525)
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