With Electric Train Heating (ETH) replacing 'steam heated' coaches, some of this class received ETH Supply when refurbished at Crewe Works during 1985 and 1986. During this refurbishment, the locomotives also received regeared CP7 bogies and the English electric generator was replaced with a Brush BA1005A alternator. Extensive re-wiring, as well as a full repaint into BR Blue Large Logo was undertaken. The modifications allowed the 're-built' locomotives to work passenger trains all year round, with the 31 strong fleet being split between Wales and Scotland, Scotland receiving the first 25 and Wales the next 6.
After the extensive refurbishment, the locomotives were allocated the 37/4 sub-class, following the trend of renumbering 'ETH' fitted locomotives xx/4s, (e.g. 47 4xx and 31 4xx).
The next chapter saw the entire sub-class pass to Transrail, which was one of the three regional freight operating companies prior to the privatisation of the entire British rail network.
Over the years, the locomotives have received a large number of liveries: BR Green, Regional Railways, Trainload Grey, EWS, Transrail, BR Large Logo and Mainline, to name a few.
The North Wales Coast Line from Crewe to Holyhead, The Rhymney Valley Line, The West Highland Line, South Wales Mainline, and Devon and Cornwall all benefited from the use of 37/4s. They are were operated by EWS and often found use on Railtours and aluminium traffic. EWS used to cycle 37/4s in and out of traffic on a regular basis, depending on demand. All have subsequently been sold to DRS by the successor of EWS; DB Schenker.
Loco hauled operations have taken a big hit within the past couple of years, thanks to the widespread introduction of diesel multiple units, and the replacement of loco hauled trains by multiple units, although the sub-class did hold out on the Cardiff - Rhymney Trains and indeed the boat trains to Fishguard Harbour for Arriva Trains Wales, the number range was:
37401 - 37431
Keywords:37/4, Class 37, Co Co