The SR built only a small number of suburban type coaches as several of the pre-grouping companies had constructed large fleets of modern coaches. However by 1934 the former London and South Western 48’ stock was reaching the end of its working life. Concious of the need to upgrade the stock with a minimal capital outlay CME Richard Maunsell developed a plan to re-use the exisiting bodyshells, overhauled, mounted on new standard 58' steel underframes and equiped with updated fittings like electric lighting.
These brake third coaches with two lavatories were utilised as loose coaches to increase the capacity of trains during peak hours, The lavatory stock was preferred for longer distance outer suburban services, where passengers would be more likely to require to use the facility.
By 1934, the Southern Region recognised that the short 48’ ex-LSWR stock was in need of some major attention as it was nearing the end of its working life. Much of it was built on wooden underframes, whilst some was still gas lit and so a programme of refurbishment was proposed and undertaken under Works Order L801 of March 1934 and Works Order L852A of March 1935.
The 58’ stock to diagrams 99 and 418 were created in 1935/1936 at Lancing Works, by taking the 48’ Composite body, cutting it and fitting to a 58’ Maunsell underframe. In the case of the Brakes, a 10’ guards van was grafted to one end, these were steel panelled, which didn’t quite match the finish of the rest of the wooden panelled bodywork. The thirds (to diagram 31) differ, in that the original 48’ body was cut into two sections and mounted at each end of the underframe, with a 10’ section being inserted comprising a single compartment, with two lavatories (side by side). The defining feature of all these ‘new’ vehicles was the triangular section weatherboard that ran the length of the body, disguising the join (the 48’ body being narrower than the 58’ underframe).
Diagram 98 brake thirds were rebuilt in the same way as the diagram 418 composites, but had the first class compartments refitted with third class seating, Total of 5 vehicles constructed, some of which were kept as loose coaches to provide extra capacity when needed while others formed part of 3 coach sets with a composite coach and another brake third.