The Daimler motor company had a rich and respected past of which many people, including bus operators, had an enviable loyalty. William Lyons was almost held in regard as being another Donald Stokes, that was until Leyland Motors with Stokes at the helm bought into Jaguar Daimler in the early 1960`s. Many people even today have little or no idea that Daimler also were a big player on the bus market right up until 1981, and up to the point of the Leyland take over, Daimler were the chosen operator for most of the municipal bus companies in the UK.
As with the Leyland Atlantean and Bristol VR, Daimler had also developed their own rear engined double deck chassis with the Daimler Fleetline in 1960 which was selling in steady numbers. Liking what he saw and being a true businessman with vision, Lyons sanctioned a replacement vehicle for the Daimler Freeline single deck chassis. Many components of the Roadliner were shared with the Fleetline but where the Fleetline featured a transverse engine, the Roadliner prototype featured an in line rear mounted horizontal Daimler CD type diesel with turbo charger.
Lyons paid attention to operators views when the prototype chassis was shown at the 1962 Commercial Motor Show and was convinced there would be enough interest to justify putting this into full scale production at Coventry. The Daimler board decided that they were to finish mass production of their CD diesel engine and opt for the ever popular and ultra economical Gardner engine, but this lead to a huge problem. Following a meeting between Daimler and both John & Hugh Gardner, Daimler were told there was no extra capacity available for them.
Gardner back in those days exerted some serious influence over chassis builders, so popular were their engines that they would often add a premium to their costs. Gardner engines were hand made and had a solid reputation for longevity, fuel economy and reliability, many operators both bus & truck had made their fortunes by using the Manchester company`s engines – and Gardners knew it. Hugh Gardner was a first class engineer but a poor business man and suggested that any further capacity would come with a hefty premium.
Daimler were having none of this, and spurned on by Hugh Gardners demands William Lyons searched around for a suitable power unit. Chrysler-Cummins were an American diesel engine builder that were desperately looking to gain some kind of foothold in the UK and European market. Famed for their heavy automotive & marine diesels, they had introduced a range of V6 & V8 high speed diesels for smaller vehicle types boasting incredible power to weight. Daimler entered a supply agreement with Cummins at a very favourable cost, but the price was payed in other ways.
The V6 diesel would not fit into the Roadliner engine bay, so a hasty redesign of the tail end of the chassis took place. Rather than feature a horizontal engine, the chassis now featured a Y shaped kink beyond the rear axle to take the engine both vertical & in line. There had been plans to enter a building agreement with Cummins, but eventually the V6 VI-M series engine was built in Shotts in Lanarkshire and Darlington, in a brand new plant which to this day, still exists. Owing to Cummins superb PT (pressure timed) fueling system, this compact high revving V6 produced a colossal amount of power.
Its maximum output was rated at 195bhp in coach chassis tune which was staggering considering an equivalent Gardner 6HLX which was larger in capacity, developed 150bhp at the highest rating. Rather unwittingly, Daimler had developed not only a bus chassis but a high powered coach chassis too and operators initially beat a path to the Coventry doors of Daimler to place orders for this brand new incredible chassis. At first, order books were heaving as Jaguar Daimler struggled to cope with not only bus chassis, but the E-Type car also.
But very soon, it became obvious that something was wrong with the Roadliner as operators started to suffer serious shortcomings with vehicles, and it was all driveline related. The Daimatic semi auto gearbox could simply not cope with the level of power going through it and matters relating to burnt out brake bands and even gearbox fires became common. Cummins engineers de-rated the engines in service buses down to 150bhp in order to prolong the life of the transmission, but other serious design problems became apparent of a magnitude that Daimler were never to recover from.
The engine was never really suited to intense stop start working in service buses, whereby coach applications performed reasonably well, bus versions were dogged with a whole manner of serious issues that included overheating, fouling of the delicate bullet type fuel injectors, piston failure and cracked cylinder liners. The thermo viscous fan systems were replaced with fixed blade metal fans to combat cooling problems but this made an already noisy engine almost unbearable. Cummins powered Roadliners had a soundtrack similar to an air raid siren.
Another serious matter involved flexing of the bodywork which affected the bus chassis more than the coach. Because of the redesign of the rearmost part of the frame in order to accept an in line engine, stress in the fulcrum of the chassis over the rear axle was more than normally expected for a rear engined bus. If the body was of dual door construction, this stress was exaggerated by the lack of body rigidity hence why many bus Roadliner`s were withdrawn from service at a fairly low age with fractures in the rear chassis which were virtually impossible to repair with success.
Coaxed into buying these vehicles with the promise of good performance and fuel returns, operators found them a troublesome vehicle and drivers new to this type often blew engines up through intense overspeeding thanks to the gearbox having no lock up clutch to offer any degree of engine braking when descending a hill. Potteries Motor Traction based in Stoke built up a huge fleet of Roadliner chassis as did Bournemouth Corporation, failures were so commonplace that engineers from Columbus in the USA and Darlington worked alongside the depot engineers in a bid to cure faults.
Staying on the Darlington theme, they along with Bournemouth & Eastbourne took a draught of Roadliners in 1967 all fitted with C.H Roe bodies of a dual door layout. These versions were true British Leyland vehicles to the core with Roe coachworks being a wholly owned subsidiary of BL. The Darlington fleet seemed to fare better than others, the Corporation transport department only ran services inside the Borough and the lay of the land is fairly flat terrain. One major factor with the Darlington buses was the fact that Cummins main UK engine plant was located less than a mile from the depot.
As mentioned before, Cummins did everything they could to rid the power unit of these gremlins with Indiana based engineers jetting to and fro across the Atlantic and a dedicated team of engineers and metallurgists frequently burning the midnight oil at the Yarm Road Darlington plant. Eventually Cummins admitted deafeat by admitting that the V6 I-M series engine could simply not cope with frequent stop start cycles of operation – being originally a marine engine design & not really ideal for local bus operators. By the late 1960`s the Roadliner`s reputation was in tatters, but British Leyland`s solution was far from satisfactory.
BL & Daimler dropped the Cummins option and plans were put into place to find alternative suitable power units but the design of the rear of the chassis somewhat limited the options available. The Gardner 6LX which was the industry standard oil burner would not fit nor would the Leyland equivalent – the 0.680 series. Perkins ended up supplying their V8 510 series engine which essentially was a de-rated truck unit, reliable it may have been but fitted into a bus chassis, ferociously thirsty. Down at Southall, AEC had developed their own V8 engine – the 700 and 800 series which was a superb design yet woefully underdeveloped became another Roadliner option.
The V8 800 series was rushed into production at the order of BL long before it was a proven engine, tales of main bearings failing at less than 60.000 miles became commonplace. Daimler eventually called time on the bus Roadliner after the launch of the single deck version of the Fleetline came on stream, the coach version was soon the only Roadliner available and stumbled along with dying orders until 1972. Daimler, a once respected company, never really had the same credibility after these events and less so after 1973, when all plant and equipment for bus production was moved to Leyland to free up production space for Jaguar cars.
To draw a conclusion, its interesting that after 40 have passed since the death of the Roadliner, the Daimler brand is now just a fading memory of old buses and posh cars. Today, Cummins engines power more buses the world over than any other diesel engine quite simply because they worked hard in getting to that position. The UK Darlington plant is also the world type approval centre for emission criteria and lab testing, making sure that they do all the development work rather than the customers – which was sadly wasn’t the case with the majority of British Leyland PSV or commercial offerings.
*This article first appeared on AROnline