(04 Apr 2018, 8:04 pm)MurdnunoC wrote The 51/52 was rerouted between Heworth and Gateshead via the 648/649 route when the latter was curtailed to terminate at Gateshead Metro. Prior the route of the former operated direct via Sunderland Road. The 27 was also amalgamated into the 51/52 between Gateshead and Wrekenton. Beforehand, it operated via Old Durham Road, Beacon Lough Road and Easedale Gardens instead of Gateshead Library and Dryden Road.
I don't know exactly when the 'new' 51/52 came about, but I reckon it must have been the early-mid 2000's - I certainly remember using it around 2000/01. If I had to guess, I would estimate 2004 as that's when the 610/611/632 etc. were renumbered and revised.
Sure it was before then. I left Gateshead before then and caught the 51 or 52 at some point.