This information guide has been written to share the history, information and specifications of the final iteration of the original Cooper S – the MKIII. Announced in November 1969, the MKIII as its name suggests was a new series in the mini range, introduced a new body which incorporated many changes, but retained the overall shape and appearance of the original classic.

The MKIII Cooper S is a particularly rare variant with just 1,570 units believed to have been built. The MKIII lacked some if the aesthetic differentiating factors that applied to earlier Cooper S variants, and was watered down in appearance so much that it could be easily mistaken for a standard Mini 1000 of the same era without looking closely.

With British Leyland’s rights to use the “Cooper” name ending in mid-1971, the writing was on the wall for one of the most successful sports cars of all time, and the MKIII was the last of the original Cooper S legend. This guide is intended to outline the main features and specifications of this rare and exclusive Cooper S variant. If any readers have further information they think could contribute to this guide, please do get in touch by clicking the ‘contact author’ button at the top of this page.

Production period:

Production of the MKIII Cooper S commenced in March 1970 and ended in June 1971. Vehicles were built at the Longbridge plant in England, or exported as CKD kits and assembled in overseas markets. At the time, the cost of a new MKIII Cooper S in the UK was £942.00.

Production numbers:

1,570 units are believed to have been built. This number is based on limited production records available through the British Motor Industry Heritage Trust.

Unfortunately, it is not possible to date production changes accurately because there are no records of commission numbers for the individual cars. However, there were very few changes made to the MK3 throughout its short production run.

1. Exterior features: MKIII Mini Cooper S

Body: The main change on the MKIII was the redesigned body shell. In comparison to MKII and earlier bodies, changed panel designs included the floor pans, rear seat pan, boot floor, body sides, rear seat brace panel, front inner wing valances, windscreen surround assembly, towboard with cross member, front parcel shelf and inner scuttle panel, doors and boot lid. There are also a large number or minor subtle differences (such as the front bonnet hinges being mounted to the bonnet slightly further apart than earlier models, and mounting holes for both LHD+RHD wiper positions). Many export markets cars were fitted with front towing eyes.

Doors: The Doors most notably are internally hinged on the MKIII, and now finally incorporated full length wind-up windows (replacing the earlier sliding windows). Doors now had a body coloured window frame, and fixed push-button door handles were fitted with key operated locks. The rear bootlid incorporated a larger number plate depression plus a new body coloured number plate lamp housing.

Paintwork: In a significant departure from previous variants, the MKIII Cooper S was only available in monotone paint colours (i.e. no contrasting roof colour). Refer to section 2 of this guide for paint codes, details and examples of the colours available.

Badging: The MKIII Cooper S was not badged as a Morris or Austin in the UK, but simply came under the “Mini” name. In export markets, Austin or Morris badges were applied. On the trunk lid was a simple badge reading “Morris Cooper S”. This was a rectangular badge with “Mini” in black on a silver background, and “Cooper S” in silver on a black background. On the front hood, a shield shaped badge was applied with the word “Mini” on a black background, with two light blue panels below. British Leyland badges were found at the base of each A pillar.

Chrome work / trim: Bumper over-riders were fitted to the front and rear chrome bumpers as standard, but no corner nerf bars were fitted. The MKIII Cooper S shared the same 11-slat chrome grille with the rest of the round front Mini range of 1971 (a change from the 8-slat that applied to the MKII). Plastichrome wheel arch trim was fitted along the side seam. On some cars, the fuel filler caps were painted the body colour. Otherwise, they were chrome plated. These caps were not lockable.

Glass/windows: As standard, a “zone toughened” windscreen was applied, with a laminated windscreen offered in the UK market as an option (this feature may also be found on export models as standard). A heated rear window was an optional extra. The switch and warning lamp was located on a small separate panel under the lower parcel shelf rail. This was a standard feature on export cars to colder climates (such as Canada).

Lighting: UK cars have front flashing indicator lamps with amber lenses. Some export markets had parker / side lamps built into the flashing indicator lamps. Depending on the local regulations, they may have a clear, or white lens (as opposed to amber). Some export markets may have also had additional directional indicators on the fender sides, side marker reflectors and or hazard light functionality. The rear tail lights were identical to the MK2. Some export markets received all red lenses (rather than part amber/part red).

2. Colour schemes: MKIII Mini Cooper S
  • At least 9 paint colours were available as standard on the MKIII Cooper S. We note that a couple of additional colours (such as black and police white) are suspected to have been available to special order. All MKIII Cooper S cars were onoy available in monotone colours (i.e. no contrasting roof colour was offered).
  • The Colours of Teal Blue (BLVC 18), Blaze (BLVC 16) and Bedouin were available from around July 1970.
  • Antelope (BLVC 7) was only available up to February 1971.
  • Although Royale Blue was listed as a colour available early on the MKIII Cooper S, it is considered unlikely that it was ever applied.
  • Icon Red trim is believed to only be available on pre-1970 cars.
  • On cars painted in Flame Red, the Autumn Leaf trim was ibly available on early cars (pre July 1970).
  • The trim colours Navy, Geranium and Limeflower were not available until around July 1970.
  • Black trim was no longer available from February 1971.

In the below table we set out the paint colours and corresponding interior trim colour availability. This information has been derived from John Parnell’s “Original Mini Cooper and Cooper S” book.

Paint colour/code Seats/door cards Carpets/mats
Antelope / BLVC 7 Black or Icon Red Black or Icon Red
Aqua / BLVC 60 Black or Navy Black or Navy
Blue Royale / BU 38 Galleon Blue Galleon Blue
Bronze Yellow / BLVC 15 Black or Navy Black or Navy
Flame Red / BLVC 61 Autumn Leaf, Black, Navy or Geranium Brown, Black, Navy or Geranium
Glacier White / BLVC 69 Black, Navy, Icon Red or Geranium Black, Navy, Icon Red or Geranium
Teal Blue / BLVC 18 Limeflower or Navy Olive or Navy
Blaze / BLVC 16 Navy Navy
Bedouin / BLVC 4 Autumn Leaf Brown
Black / BK1 Unspecified Unspecified
Police White / WT-2 Unspecified Unspecified


3. Interior features: MKIII Mini Cooper S

Instrumentation: The central oval instrument binnacle was retained on the MKIII, with the central speedometer showing both Miles & km allowing for metric export markets such as Canada and other parts of Europe. A fuel gauge was below the speedometer in the same binnacle. A temperature gauge was on the left, and an oil pressure gauge on the right (all gauges being of the Smiths brand). Exported MKIIIs may have been fitted with a radio from factory. In the UK market, a radio was a dealer installed accessory.

Seat trim: A new range of vinyl trim colours were introduced including Blue, Black, Brown and Beige. The MKIII trim is almost indistinguishable from the Mini 1000, with vinyl upholstery featuring a simple heat formed pattern (7 long thin pleats running through each of the front seat squabs and backs, and 10 pleats on the rear seat squabs and backs). The seat frame and pads are the same as applied to the MK2, while the covers are almost the same, but the vinyl grain is courser than on the MK2 models. Reclining seats were an option, and some vehicles bound for export markets had a special lock down catch fitted.

Door trim and quarter trim: The door trims are the same as applied to the Mini 1000 and other saloons, with three pairs of lines running the length of the door card, and one single line below. The same pattern was repeated on the rear quarter panel cards.

Trunk: The boot board was covered in course black Veltone fabric (and no longer had a stitched vinyl border as applied to earlier cars). The tool bag in the trunk was the same as on earlier models, nut now contained only the jack and the wheel brace (a plug spanner was no longer supplied).

Carpets and small trims: Carpets were colour coded to match the rest of the trim, as was the rear parcel shelf panel (refer to the paint and trim codes section of this guide). The headliner, sun visors and rear quarter trim pieces were finished in either a pale grey or off-white. The interior roof lamp now fitted on the left side of the roof. The Windscreen pillars, scuttle rail, upper dash rail and lower parcel shelf rail were all trimmed in black vinyl. The parcel shelf rail had a bright chrome finish beading. The Interior mirror has a light grey backing plate, and was fitted with a suction cup to prevent vibration.

Switches: Early UK market cars have a combined ignition lock and starter switch panel (in the centre of the dash), with toggle switches for the lights and wipers (knobs for the heater (Right) and locking choke (left)). Later UK cars (from January 1971) and most export market cars, had rocker switches in the centre dash panel for the lights and wipers, and the ignition moved to the steering column (which had an integrated steering lock). The new ignition on the column was made by “Lowe and Fletcher”. This type of lock was introduced from Commission Number N20D/850. Early export cars with a steering lock have a blanking plug over the redundant ignition hole in the centre switch panel, but the hole was deleted altogether once the steering lock became standard.

Steering wheel, column controls and gear knob: A two-spoke steering wheel was fitted (the same as the MKII), but now had a centre hub stating “MINI”.  A multi functional stalk controlled the indicators, horn, sip switch, high beam flasher. The switches for lights and wipers are still on the main switch panel. The MKIII should have a black gear knob/lever with the gear pattern printed in white.

Seatbelts: Seatbelts in the UK market were dealer installed on pre-1971 cars, but from January 1971 became a legal requirement. Recommended types at the time included “Kangol Magnet” static belts or “Britax” inertia reel belts – both attaching to a centre tunnel buckle fastening.

Heating and ventilation: The MK3 heater is quite different to the MKII. It is a Smiths heater, the same fresh air water valve type – but now the air intake is through the mudguard rather than the bulkhead/firewall. A higher output heater was installed on export cars bound for colder climates. The heater was standard on all UK market cars. An optional extra on the MKIII was a fresh air ventilation system, with black plastic vents fitted to either end of the dashboard liner.

4. Car number, commission number, Body number & engine number: MKIII Mini Cooper S

MKIII Cooper S Chassis number / car number:

The MK3 Cooper S had a chassis number / car number prefixed by “XAD1”, with a unique car number between 34127 and 458987. The prefix is interpreted as follows:

X = nothing/check digit

A = A series engine

D = Cooper S or 1275 GT

1 = Short nose (round front)



The chassis/car number for the MKIII Cooper S appears embossed in a small aluminium tag, noted as “CAR No.” The tag is located on the top edge of the bonnet slam panel, in front of the ignition coil.


Commission number:


“20” indicates the new mini project number for the MK3.

“D” indicates the Cooper or GT model variant.

This was then followed by the car’s unique commission number, which was usually supplemented with the letter “A”. “A” indicated that the cars were built at the Austin factory at Longbridge, Birmingham. The second suffix is “B”. indicates the cars were built in Belgium, in Seneffe

Unlike the car number, the Commission number series was unique to the model, starting with N20D/101A for the first car built, and ending with N20D/1668A for the last car built.  Supposedly, however, a genuine Cooper S with Commission number N20D1670A is known to exist. This indicates that the 1570 cars were built, 778 of which were UK market vehicles.


Like the chassis number, the Commission number also appears on a small aluminium tag sitting to the left of the chassis number / CAR No. tag, on the top edge of the bonnet slam panel directly in front of the ignition coil. The number is embossed on the tag, and the tag feature a red border.

Body number

A MK3 Cooper S body number is prefixed with the code B20D. MK3 bodies still had the FE prefix number on a large steel tag which was welded to the body shell. 

The FE numbers can’t be used to identify a mini variant. The car number allocated to the MK3 S is taken from a series of car numbers allocated to all minis at the time that went through the factory. Evidence suggests there were small batches of particular models produced together (eg – 10-20 consecutive numbers at a time).

Engine number

12H397FH or 12H398FH

The MK3 Cooper S had engine prefixes starting with 12H, followed by a code number of either 397 (which meant it was fitted with a C40 Dynamo) or 398 (which meant fitted with a 16ACR Alternator). That prefix is followed by the letter “F” (which indicates twin carburettors), and finally “H” for “High Compression”. However, frequently the letter “H” is missing from the engine tag.


The engine number, like all mini engines, is located on the top front edge of the engine block, just above the alternator. The MK3 Cooper S had the number embossed on a small aluminum tag that’s riveted to the block.

5. Mechanical features: MKIII Mini Cooper S
  • Suspension: The vast majority of MKIII Cooper S cars were fitted with hydrolastic suspension (like all previous Cooper S variants). The part numbers are (front: 21A2012) & (back: 21A2014). Police cars were equipped with different displacer units with part number 21A2010 both front and rear. Several books and forum discussion suggest that some very late cars had dry rubber cone suspension, but there is no factory documentation supporting this assertion. All MKIII Cooper S cars have redundant shock absorber mounting points on their inner mudguards – on account of the fact that other models in the mini range had rubber cone suspension.
  • Engine paint colours and finishes: The normal green engine colour finish changed to black very early on in MK3 production, and therefore some very early cars may have had green engines the same as the MKII. The vast majority of cars had Both the engine and its accessories painted black. There were no stickers / badges on the rocker cover. The coil should be a natural metal finish.
  • Component part specs and ID numbers:
    • Cam shaft is marked AEG 542 with a spider drive for the oil pump instead of the pin drive found on earlier models.
    • Cylinder head is part # 12G1805, stamped adjacent to the thermostat housing. The casting number is 12G940.
    • Crank was no longer Nitrided, but was of the cheaper Tuftrided variety.
    • During production, the original forged valve rockers were changed to the pressed steel type.
    • The engine can still be identified by the additional stud bolt on the engine head, tappet chest covers and the Duplex timing chain (i.e. 11 studs total vs the standard 9).
  • Engine cooling: A three core radiator was standard as per the MKII S. Only the lower part of the two piece radiator cowling and some of the brackets are unique to the Cooper S in comparison to other models in the range, due to the larger size of the radiator. A 13 row oil cooler was fitted (same as the MKII). An 11-blade plastic fan was applied to most UK market cars, but a 6-blade steel fan is believed to have been applied to some export market cars. All cars had the grille panel with the diagonal strut, to clear the central horizontally mounted oil cooler.
  • Brakes: The brake Servo was a Lockheed “Type 6” unit (i.e. 6 inch in place of the older 5.5” unit). This was significantly different from the earlier unit. Export cars to France and Benelux had a transparent brake reservoir. Front discs (7.5“) and rear drums are the same as on a MK2. It does not appear that dual circuit brakes were ever fitted to the MKIII Cooper S.
  • Tyres: Dunlop 145-10 SP68 tyres (with tubes) were specified as standard on the MKIII S. Both 3.5” and 4.5” wide ventilated rims were available, finished in silver paint.
  • Electrics:  
    • All MKIIIs had negative earth electrics.
    • The original battery was a CL7 (or dry charged CLZ7 for some export markets), rated at 34Ahm as on the MKII, but the MKIII fitted with an alternator had a higher capacity 45Ah type CA9/7 battery. D0uring production, a new Lucas ‘Pacemaker’ battery with a translucent case and automatic filling was introduced (believed to be from commission number N20D/1157.
    • All police spec cars had an alternator – and apparently the alternator was a more commonly fitted item (many cars have since been converted to alternator).
    • The ignition coil is fitted with a bracket to the front cylinder head stud, at the end above the clutch housing.
    • Lighting: Headlamps were sealed beams with built in side lamps (parkers). This was the case for British and Japanese market export cars. For other RHD markets, the cars had sealed beams, and separate side lamps. LHD markets are supposedly less consistent: Canadian exports likely had Sealed beams and separate side lamps. Cars to France had non-sealed beam headlamps with yellow bulbs and built-in side lamps. Most cars for Europe (except France and Italy) had non-sealed beam units and built-in side lamps up to commission number N20D/140, but were fitted with sealed beam lamps thereafter. These had built in side lamps for Germany, Denmark and Austria, but cars for other European markets had separate sidelamps. All MKIII cars had noticeably larger side lamp Plinths (on the lower fender panels) when compared to earlier cars.
    • Horn: A single clear hooter horn is fitted to most cars. However, several export cars may have twin horns (twin pitch high and low note horns were a legal requirement in France, for example).
  • Exhaust system: The MKIII S has two silencer boxes fitted. One narrow silencer sits at the rear of the centre tunnel in the floor pan, and a fatter/shorter silencer sits under the boot floor, in the part of the exhaust pipe that is angled toward the rear left corner of the car.
  • Fuel system: Twin SU HS2 1.25” carbs were applied. Specification of left carb is CUD9123, and right hand carb is CUD9124). The standard needle is “M”. The damper springs are red, while damper caps are knurled and made of black plastic. The HS2 has a fatter dashpot housing and shorter neck than the HS4 – apart from being a different throat diameter. An SU electric fuel pump of type AUF201 was applied, fitted as usual to the rear subframe like earlier S cars.
  • The corner of the air filter housing was cut off / flat in the corner, to allow clearance of a new semi circular washer bottle now fitted to the bulkhead.
  • Wipers/washers: Two speed wipers may have been fitted to some export models, but the UK cars had single speed wipers, which parked in front of the passenger. Early MK3s had the same mechanical windscreen washer pump as the MK2.  From Commission number N20D/865 it appears that a different type of washer is fitted, with a shorter barrel for the plunger and semi-circular rather than round water container. In some export markets they may have required Thermal control unit (preventing the wipers from being overloaded), and induction heaters for the carburettors.
  • Power and performance specs:
    • Compression is 9.7:1
    • 76 bhp at 6,000 RPM
    • 79 lbf. Ft torque at 3,000 RPM
    • 0-100 km/hr = 10.4 seconds
  • Gearbox: As standard, an all synchromesh gearbox was fitted with slightly different ratios as set out below:
  • First: 3.33:1
  • Second: 2.09:1
  • Third: 1.353:1
  • Fourth: 1.00:1
  • Reverse: 3.35:1

A range of Special Tuning part options remained available including:

  • Twin 1.5” HS4 carburetors;
  • Weber twin choke Carburetor;
  • Competition Clutch;
  • Lightened fly wheel;
  • Alternative Camshafts;
  • Competition exhaust manifold;
  • Competition Pistons;
  • Competition valve springs;
  • Competition oil cooler;
  • Full length sump guard;
  • Alloy wheels;
  • Wheel arch extensions;
  • Lightweight seats;
  • Alloy (or later, fiberglass) body panels;
  • Rally-spec front hydrolastic suspension displacers were available, marked with a red band (part number 21A1819);
  • Rear anti roll bar;
  • Competition oil cooler;
  • Magnesium minilite wheels;
  • Close ratio gearbox (see specs below) - Straight cut close ratio or standard ratio gearbox; and
  • Sump guard.

The above items are detailed in in tuning book publication C-AKD 5096. See the full publication at the following link: https://mk1-performance-conversions.co.uk/pdf/AKD-5096.pdf

Special Tuning Close ratio gearbox specifications:

Overall ratios (based on final drive type chosen: a customer could select which final drive type they wanted):

[Insert table from text here]

6. References, documentation and useful links

The MKIII Cooper S had limited promotional material produced – we presume partly due to its low production numbers but also perhaps due to the fact the Cooper name was being phased out in the mini range. It’s also likely that the company was focused on promoting newer performance names in the range such as the 1275 GT.

We have managed to find a small sample of original promotional documentation on the MKIII Cooper S, as shown in the images. If any enthusiasts have further information or images related to the MKIII S, please click the “contact author” button at the top of this page.

The following links have been particularly useful in preparing this guide


The following book publications have been relied on in preparing this guide:

  • The Complete Catalogue of the Mini by Chris Rees
  • Original Mini Cooper and Cooper S by John Parnell.
  • Mini Cooper and S by Jeremy Walton (1982)