Aldenham Works

London Transport's Aldenham Works overhaul procedures 

(I am grateful to both Gordon Mackley and Brian Watkinson who have provided all the information for this page. Ed.) 

LT opened the Aldenham Works in 1955/6 as its Chiswick Works had insufficient capacity to support both their current and growing fleet.  LT introduced a new vehicle maintenance & overhaul Float System at Aldenham and it was realised that there would be a large number of buses, with current, valid, road tax licences, undergoing overhaul at any one time. 

Overhauling any bus of LT's extensive fleet of RT's etc. involved parting the body from its chassis/running units and the necessary work performed on these separate entities would differ for each vehicle and part thereof.  In all fleet operations, legally (and normally) all chassis are aligned with the vehicle registration number and thus to accompany fleet numbers. However in LT’s case neither the chassis, nor body, necessarily remained associated with the stock number and therefore the registration number.

Aligning the overhaul dates with road tax expiry was not practical and therefore LT was potentially faced with paying for more road fund licenses than buses on the road. To prevent this, LT obtained governmental dispensation to transfer registration numbers from one chassis to another (and thus also the stock number) to enable continuous licensing [see Note 2].  However the Works Float System was not simply to facilitate licensing; it was also a production control system effectively used as a means of controlling the mix of buses in the Works at any one time.

In 1955 a large number of RTs, RTLs and RFs were taken into Aldenham and their identities disappeared, this was the start of the Works Float and enabled overhauled buses to leave the Works with a different identity to that it arrived with. The Works Float System worked by bringing in the required extra number of delicensed vehicles, whose stock numbers had not been allocated to buses leaving the Works, at the same time as these buses went in. These Works Float buses were then overhauled and when ready for service again allowed a similar number of buses to come in for overhaul, thus increasing the number of vehicles of that type going through the Works. This system was also used for the overhaul of the RTWs and the Metro Cammell bodied RTLs [see Note 3].

Bodies on RTs, RTLs, RTWs and RFs did not necessarily go back on the chassis they arrived at Aldenham with. And on the occasions it happened it would be very unlikely that they left with the same stock number and registration plate. Within the RTs and RTLs bodies often swapped between types. In 1964 a number of RTLs received headboxed RT 10 bodies to get later bodies off RTLs and onto RTs. And in 1965 a deliberate programme was undertaken through overhaul and specific body changing, to replace all the later RT8/2 bodies on RTLs with earlier RT3/1 and RT8 bodies. 

The Works Float enabled for example a reduction of the number of red RMs being overhauled when the first RMLs were due for overhaul and also the RMCs. Prior to these variants being overhauled, a number of RMs with Works Float identities were output to garages reducing the number of red RMs in the Works, a small number of RMLs and then RMCs went into the Works Float to start off the programme(s). When the RMLs and RMCs were all done (and their respective float buses went back on the road), a number of delicensed red RMs went in to the Works Float to bring the number of red RMs going through the Works back up to as before.

The stock numbers of Works Float buses remained in the Works Float until such times as there was a requirement for the number of buses of a particular type being overhauled to be reduced. When this happened, the required number of stock numbers were expelled from the Works Float by being applied to vehicles leaving the works and returning to service. This practice reduced by the requisite number, the number of the specific type in the Works as no vehicles came in to take their place.

With the Routemasters the Works Float was regularly rotated rather than have a large number of 'numbers' hidden away for many years as happened with the RTs and RTLs. 

The stock numbers of buses to be overhauled were published in a two-week 'programme of buses to be overhauled' which detailed which buses were to be made ready for collection at garages on a daily basis. This was distributed widely to the garages, District Offices and Rolling Stock Buses at Chiswick at least ten days in advance.

The "new identity" of a bus was allocated in the Mount Shop when the overhauled body was put on the overhauled chassis, (some 4 or 5 days before any incoming bus with that stock number was due in the Works). The new number to be applied to the bus was recorded on an 'Advice of body and/or chassis change at overhaul' form. The new 'transfers', registration and chassis plate on the N/S front dumb iron were applied on the Paint and/or Finishing line.

Typically chassis were quicker to overhaul than bodies and so the next completed chassis received the next suitable overhauled body. Thus, not only did the chassis/body combination change but also the ‘complete identity’ (registration & stock number) could belong to neither.  In the case of the Routemasters, the two sub-frames (running units) were regularly interchanged which often resulted in buses changing engine type [see Note 1].

Therefore, after overhaul, RM’s were usually not the factory-original vehicle. And because many bodies were needed as a ‘float’ in the system, some RT family vehicles' identities actually disappeared completely for many years. (So much for ‘bus spotters’ underlining numbers in their Ian Allan ABC books!)

This approach of course could only be applied to large fleets with interchangeable bodies, such as the RT’s and RTL’s (and later RM’s). The process was not possible for small fleets, with few vehicles being overhauled at any one time.  Occasionally mistakes were made; and it has been reported that two vehicles were once in existence with the same registration and stock numbers.  However, as the tax disc holder(s) were either swapped or moved from vehicle to vehicle at Aldenham, it would not be possible for two similarly licensed buses to be in operation simultaneously.

Prior to the inter overhaul repaints starting in April 1967, a large number of RTs RFs and RMs were 'expelled' from the Works Float to reduce the numbers of buses being overhauled by roughly fifty percent.

It should be noted that the concept of body swapping on overhaul at Aldenham was not new, as many earlier types STs, STLs etc. had body swaps during overhaul at LT's Chiswick Works.

A typical example of the confusion resulting from LT's body swapping can be seen on the page dedicated to RT4325.

The Aldenham facility was closed in 1986 resulting in the overhaul of the remaining RM fleet being outsourced. 

[Note 1] Buses changed engine type only as a result of there being a different engine in the chassis/running unit to which the body was applied. Aldenham only changed engines and gearboxes during overhaul if they failed on road test, which was very rare. This work was carried out by the garages as necessary. However, Aldenham changed all safety related items irrespective of date last fitted (i.e. complete axles, steering boxes etc.).

[Note 2] For any vehicle undergoing overhaul at Aldenham (and Chiswick too) its body & chassis were often (usually) interchanged with bodies & chassis of other similar vehicles; that resulted in Registration Plates (and thus Log Books) being applied to a body/chassis combination that was not the original.  The Log Book & Tax Disc being Department of Transport official documents cannot ever be altered, thus a Tax Disc referencing a particular Registration Plate would always reference the original Chassis for that vehicle.  In order that a bus could leave Aldenham the same day as one with the same LT designation number & Registration Plate came in for overhaul (and the Tax Disc swapped over), it was necessary that the actual chassis could be changed.  Although LT had governmental dispensation to transfer registration numbers between vehicles, one of the conditions of LT being allowed to change the chassis to one different from the chassis detailed in the Log Book was that the change must be to a vehicle of the exact same type, dimensions & weight etc. 

Occasional clerical errors did occur however, where buses had been inadvertently released from Aldenham with Registration Plates, and thus Log Books detailing different dimensions or weights from the bus to which that Registration Number was now applied. This required the Log Book(s) to be sent away to be altered to reflect the different weight or dimensions newly attributable.

[Note 3] To understand more clearly how the Works Float system operated in practice the following example may assist:

Beginning the system in 1955 necessitated a large number of RTs, RTLs and RFs being taken into Aldenham and losing their identities; this was the start of the Works Float and it enabled overhauled buses to leave the Works with a different identity to that they had arrived with. Continuous licensing was enabled and the status quo continued until it was necessary to change the mix of buses being overhauled. This is where the production control side of the Works Float system came into use.

The production control side of the Works Float system is best explained using this example:

When, say, the Green Line RTs were due to be overhauled, it was necessary to start a float of these to allow identity changing and continuous licensing, but there was also the need to reduce the number of, say, red RTs being overhauled at the time.

Firstly a number of Green Line RTs were delicensed, these buses went to Aldenham and their stock numbers went into the Works Float. At the same time, a similar number of red RT numbers from the Works Float were allocated to buses being overhauled and these red RTs left the Works.

The "Works Float" Green Line RTs were then overhauled and when ready for service again they allowed a similar number of licensed Green Line RTs to come in for overhaul and their identities to be taken by those leaving the Works.

When all the Green Line RTs were all overhauled, the last ones to leave the Works were given the identities of the original Works float batch. Then a number of red RTs were delicensed and they entered the Works Float thus restoring the balance of buses in the Works.

A practical result of the procedures carried out at Aldenham can be seen here on the RT4325 renovation page

More information about the Aldenham Works can be found here:

Here is an informative video of the Aldenham Works: