Layout
When construction began around August 1958 the plans for the interior layout were as follows - the non-gangwayed high density sets were to have a capacity for 350 2nd class passengers in SR EMU style saloons and semi-compartments. The front saloon in each DMBS was to have 45 smoking seats with a swing door through to a 32 seat non-smoking section, beyond which was the guard and luggage area, although there was no through access. The TS had one large 52 seat smoking saloon, a 22 seat smoking saloon, a 12 seat "ladies only" compartment and a 22 seat non-smoking compartment. There was to be no through access between the compartments/saloons. The TS(L) had an 11 seat no-smoking compartment, a 29 seat smoking saloon, 2 toilets side by side, a 29 seat smoking saloon and a 21 seat non-smoking saloon. Doors on all bulkheads in this vehicle gave everybody in it access to the toilet.

By the time the sets were delivered a few alterations to these plans had taken place. In the TS there was no longer any separate ladies compartment, with the seating bay now linked to the non-smoking compartment forming a saloon of 32 seats, a loss of 2 seats for the vehicle. The DMBS no longer had the swing door between the two saloons, meaning an extra 2 seats in each car of this type. The number of seats in a set was now increased by 2 to 352. Interestingly, the door between the saloons in the DMBS was later added, reducing each DMBS to 76 seats, and a 4-car set to 348 seats.

Underframe
The underframe was of mild steel welded construction, 63ft 5in long over headstocks, and 46ft 6in between bogie centres. The solebars were a 7in x 3 1/2in channel section, and the main longitudinals were 10 3/4in deep welded angle and plate. The buffers, supplied by Garringtons Ltd, were the self contained type with rubber springs, supplied by George Spencer Moulton & Co Ltd, situated behind the underframe bolster. Rubber springs for the drawgear were supplied by the Clyde Rubber Works Co Ltd.

Bodyshell
The body and roof framing were of conventional BR design formed of 1/8 in thick steel of "top hat" section, with bodyside and roof panelling of 16 swg sheet steel. The cab roof domes were of moulded polyester glass laminate, incorporating four digit route indicators (the first DMUs to have them).

The floor consisted of 3/4 inch thick blockboard with 1/4 inch thick asbestos insulation sheet and a 16 swg light alloy panel on the underside. The interior of the bodyside, bodyends and roof space was filled with glass fibre for heat and sound insulation. Doors were from Lightalloys Ltd, and windows from Becket, Laycock & Watkinson Ltd.

Bogies/Brakes
The mild steel conventional design bogies had individual members partly fabricated and the main framing members rivited together. The centre castings and side friction castings were carried on resilient mountings and the bolsters had Armstrong hydraulic "Antisway" dampers to give some control of the swing-bolster movement. Timken taper-roller bearings were used throughout. The Gresham & Craven A.I.V. quick release system was used with engine driven Clayton Dewandre exhausters.

Engines
Each power car had two Rolls-Royce 823 series C8N horizontal engines, with eight cylinders of 5 1/8 inch bore and 6 inch stroke. Built at the Rolls-Royce Oil Engine Division's Sentinel Works in Shrewsbury, they incorporated a CAV hydraulic governor mounted on the fuel pump. Maximum power was 238hp at 1,880 rpm, giving a total of 952hp for a set and a power/weight ratio of 7hp per ton for the unit. Engines and torque convertors were unit in construction and slung below floor level on Metalastik flexible mountings, and each unit drove one inner axle. A Graviner automatic fire extinguishing system would shut down any affected engine and ring fire alarm bells in driving cabs and brake vans. There were four extinguishers per engine (most DMUs had one per engine). The fuel tank capacity was 95 gallons for each engine which gave a range of about 500 miles.

Transmission
The Crewe built three-stage Rolls-Royce DFR 10,000 series torque converter changed to direct drive at 46mph. For this to happen, the engine was throttled down for 4 seconds automatically and the clutch incorporated in the torque converter casing was engaged by means of a Smith-Stone electro-pneumatic control system incorporating Westinghouse ep valves and worked on voltage sensitive relays fed by the axle-driven speedometer generator.

When the train speed fell to about 39mph there was an automatic change out of direct drive back to torque convertor drive without de-throttling the engine. Under this condition the free wheel prevented shock loading of the transmission. The torque converter gave a torque ratio of 5:1 at stall and this decreased as tractive effort dropped. The absence of gear changing meant that there was no interuption of effort during acceleration to 46mph. The direct drive above that speed, up to the nominal maximum of 70mph, gave maximum efficiency.

The transmission fluid was originally fuel oil, fed by an engine driven charge pump and returned to the fuel tank after passing through a heat exchanger. It became obvious that using diesel was a fire risk, and they were converted to use their own hydraulic fluid (Shell Talona), possibly around the early '70s. A freewheel ensured the mutual independence of the engines.

Connected to the torque converter by cardan shafts was the 2.97:1 ratio reversing SCG RF28 final drive. When the vehicle was stationary, if the selector dogs became butted to hinder engagement during the selection of a change of direction of motion, an automatic device signalled the torque converter control to cause slow rotation of the cardan shaft. Neutral gear could be selected in cases such as when the automatic coolant and lubrication fault protection shut down the individual engine. This required a local manual control to be operated by the driver. There was a carriage key switch on the solebar enabling the isolation of a single axle.

Electrics
The the 440ah 24v batteries were charged by engine driven generators on the power cars, and axle driven generators on the trailers. Generators were supplied by J Stone & Co (Deptford) Ltd. Inter-car connection was by 19-core PCP sheathed cables with 19 way plugs for which sockets were provided at the corner of each car.

Interior
Interior plastic wall paneling was in matt yellow, charcoal and buff, and wood mouldings were mahogany, polished in the natural colour. Ceiling panels, also plastic, were a matt ivory, and the linoleum was a gun-metal marble finish.

Seats were back-to-back in a 2+3 formation (6 across bulkheads). They were formed from steel tubular framing, covered in cut moquette of tan, yellow and black horizontal stripes. The seat ends were enclosed with a solid timber frame faced with a semi-matt green plastic panel.

Each car had two Smiths thermostatically controlled oil-burning combustion heaters mounted on the underframe. Fresh air was drawn in through a filter and heated, after which it passed through a system of ducts under the floor with outlets into the car.

Interior lighting was supplied by the batteries stepped up to 240v, 1,000/1,665 cycles ac by individual AEI transistor oscillators, each arranged to feed one 4ft 40W fluorescent lamp arranged down the centre of each vehicle. The cab and van lighting was independent from the passenger lighting, and was controlled by two-way switches adjacent to the doorways.

Cab
In the cab were "engine running" indicator lights (worked by oil pressure switches) for 12 engines (six power cars - enough for the maximum of 3 x 4-car sets), air pressure indicator lights for six power cars, two engine starting buttons (one for all engines on each side of the train), one engine stop button, a guard to driver signalling buzzer, a telephone for communication between driver and guard, and a fire bell which operated in conjunction with an automatic extinguishing and engine stopping system.

Left: Michael Kaye 55A On the drivers control desk were an electric speedometer, an air pressure gauge, duplex vacuum gauge, switches for controlling the demister and route and destination indicator panel lights, a dimmer switch for the panel lights, horn control, a windscreen wiper control and the key-operated main battery switch.

As the sets were built with blue square multiple working, they could be worked with units fitted with conventional 4 speed gearboxes. For this reason the speedometer was calibrated to indicate when gear changing was advisable, and the drive selector on the drivers right was marked "D, 3, 2, 1" to change the gears on multied vehicles with mechanical transmission. Above was the mechanically-interlocked reverser controller, and on the left the engine speed controller, which had five positions and incorporated the deadmans handle. When the handle was released the engines returned to idling, the gear to neutral, and after a five-second display the brakes applied. The parking brake was midway across the cab.

Blue Square Becomes Red Triangle
The sets were delivered with the Blue Square coupling code, which allowed them to couple to any other Blue Square sets (which the majority were). However, the driver had to alter his driving technique when a Class 127 was coupled to a set with mechanical transmission, and the Class 127s had speedometers segregated into four parts to help with this.

Power could not be applied until the final drives were engaged properly. Selecting any gear put the set into 'drive'. There was trouble if the driver had a mechanical set at the back and forgot to change gear - any speed was possible in gear - causing major problems for the gearbox in the mechanical set. Apparently there was a plate in front of the driver which could be lifted to reveal a reminder (something like "Gearbox Stock"). 

As the sets worked their services exclusively, coupling to other units was a rare occurrence. However, when some Class 112 Cravens sets (Rolls Royce engines and mechanical transmission) were transferred to the Moorgate line, this did occur. On the 27th June 1968 a Class 127 coupled to one of these Cravens was travelling at high speed near St Albans when a gearbox seized and caused a serious fire, and was attributed to improper driving (details). While most of the Cravens were withdrawn in the five months following the incident, the rest were restricted to Kentish Town - Barking services. In 1969 the 127s were rebranded the Red Triangle coupling code to prevent such an event happening again, though there were no technical modifications done to justify their own code. As they were still wired for Blue Square, they would have been in no way compatible with the West Riding Derby Lightweights had they still been in service, which had originally carried the Red Triangle code.

Gangways
Although the Class 127 sets were never fitted with gangways, soon after the trailers were sent to Tyseley they were given gangways to allow more flexibility in the type of service and area of operation that could be worked by the units, while providing better passenger comfort. The need for through gangways was necessary for the increasing number of 'Paytrain' services and as more use was made of DMUs for summer holiday and long distance relief passenger services.

The work was done at Carlisle Currock C&W repair shops, and involved cutting an aperture in the car ends following the removal of the interior and fascias and insulation material. New gangway hanger brackets were manufactured, and the gangway connectors and doors were taken from withdrawn Class 120 trailers. As they already had through access inside, no other interior work was required. The vehicle ends also required the run of the passenger communication cord and the water filler pipes to be repositioned.

TSL 59596 was the first Class 127 trailer to be tackled in November 1983. It was part of set TS 520, operating with power cars 53827 and 53880.

Length over headstocks	63' 5"
Width over body panels	9' 0"
Height - rail to top of roof	12' 4 1/2"
Centre of bogies	46' 6"
Bogie wheelbase	8' 6"
Wheel diameter	3' 0"

For many years the Class 127s had to carried tail lamps, even though they had marker lights built in. This was because union agreement over the use of the red bulbs in the headlamps was not given until late 1982.