There were several different flavours of Routemaster. The basic red RM 27’6" long powered by a derated 9.6 litre AEC AV590 engine set to deliver 115 bhp at 1800 rpm and equipped with a fully automatic gearbox. The vehicle was of semi integral construction having a 99.5% aluminium body with two subframes an ‘A’ Frame mounting the engine and attached fluid flywheel and a ‘B’ Frame mounting the 5.22/1 spiral bevel rear axle. The vehicle had independent front suspension with upper and lower wishbones. At all four corners it sat on coil springs. The four speed epicyclic, electically-controlled air-operated gearbox was midships mounted attached to the body. The Electrical Control sytem was made by SCG or CAV. A motrocycle style alternator was driven from the gearbox supplying variable voltage to an early ECU or panel which determined the gearchange points from accelerator position, torque and roadspeed. The driver could manually select all gears (except 3 and 4 when stationary). With the gear selector in 4 the gearbox operated in automatic mode. The vehicle had full power hydraulic braking, pressure being generated by an hydraulic pump belt driven from the gearbox input shaft. The braking system was split into a front and a rear system with pressure stored in two accumulator sat 1200psi. These were precharged to 550 psi with air so that if the drive belts or the pump failed full braking was still available. The braking system operated at 600psi with the low pressure warning flag falling at 700 psi ; a very safe system. The wheel cylinders were all external to the brake drums. The braking system was sourced from two manufacturers Lockheed and Clayton Dewandre, most of the system was interchageable between the two manufacturers. The vehicle weighed 7tons 5 cwt unladen and 11 tons 10 cwt fully laden. Seating was for 64 passengers. Apart from a few early vehicles with DC charging systems the bulk of production had alternators from CAV or Simms. Early vehicles had three 8 volt batteries which were soon replaced with four 6 volt batteries. They had a 29 gallon fuel tank
There were three variations to the basic RM . Around 600 were powered by the Leyland 600 engine. This was to Power Plus spec, but not actually sold as such. The settings were identical to the AEC unit. Around 170 RMs were built with the 11.3 litre AEC AV 690 engines derated to 115 bhp. LT was constantly experimenting with alternative specifications for its buses with the most significant departure being a batch of 50 vehicles delivered with rear air suspension from Dunlop and Firestone. These vehicles were fitted with an additional air tank. All RM were Red.
The RML ( Routemaster Long) was 30’ long with a two foot long bay being inserted between bays two and three. These longer vehicles required an additional propshaft and centre bearing. They weighed 7 tons 12 cwt unladen and 12 tons 6 cwt laden with their 72 passengers. In all other respects they were the same as the RM except that all used the AV590 and RM settings. A significant number of RMLs were green.
The RMC ( Routemaster Coach) 27’ 6" long carried 57 passengers in quite luxurious extra deep cushioned seats. All were AV 590 powered at the RM settings. The gearbox ECU was omitted , all gears being directly selected by the driver. The final drive ratio was 4.7/1 The body was fitted with power operated folding doors. The buses were fitted with an extra fuel tank bringing capacity up to 41 gallons for the longer routes.These vehicles were faster than the RM or RML but since it weighed 7 tons 16 cwt unladen and 11tons 10cwt laden hill climbing with a higher ratio axle was rather slow. The RMCs were green.
The RCL ( Routemaster Coach Lengthened) 30’ long, was considered the pinacle of luxury. The longer wheel base gave a much better ride than the rathe choppy ride at speed of the RMC. These were powered by the larger AV690 set at 150bhp at 1800 rpm. The same 4.7/1 rear axle was used making these a fast powerful bus. Seating 65 these were 8 tons 3cwt unladen and 12 tons 7 cwt laden. In other respects they were similar to the RMC
AEC / Park Royal only managed to sell two small batches of Routemaster to any customer other than London Transport. Both were front entrance bodies with power folding doors and resulted from the one experimantal long wheelbase RMF 1254
(Routemaster Front Entrance). As built it was mechanically similar to an RML. This vehicle went on a sales tour, not quite as far as RML 898 which went to the USA but around Britain being sampled by East Kent who did not order and neither di Liverpool Corporation. Northern General however were interested an specified an Leyland 600 engine and a 5.2/1 Leyland worm drive rear axle for the two batches (total 50) ordered. In service these seated 72 weighed 7 tons 14 cwt unladen and 12 tons 6 cwt laden. One vehicle was extensively modified by Northern General’s works following accident damage. emerging as normal control “Wearsider”.
The other order was from BEA for airport coaches to take passenger from the West London Air Terminal to Heathrow airport. Thes were eventually identified as RMAs ( Routemaster Airport). All towed luggage trailers (88 were ordered to accompany the 68 Routemasters. The RMAs were fitted with the AV 690 engine set to 175 bhp at 2200rpm and driving a 4.08/1 diff. They were flying machines which regularly ran at 70 mph along the M4 although oficcially limited to a speed limit of 50 mph.Seating 56, these 27’6" long vehicles weighed 7 tons 14 cwt unladen and 12 tons 6cwt laden.
There was one extra Routemaster, FRM1 . 31’6" long. This was a sadly abandoned project. A Front entrance rear engined Routemaster built to rival the Atlantean and Fleetline. Powered by an AV691 set at 150bhp @1800rpm it weighed 8tons 9cwt unladen and seated 72 at an all up weight of 13tons 6cwt. The vehicle is in the London Transport Museum.