Problems with the class were experienced immediately, with the first 25 locomotives being withdrawn in October 1951 after several complaints were received from crews regarding the driving wheels shifting on their axles.
They were subsequently modified, and released back into revenue-earning service.
 Initially the return cranks on the main driving wheels were of LNER block type, as seen on Arthur Peppercorn's A1s and A2s, but this was changed to the simpler LMS four-stud fitting.
This was the result of a problem of overheating bearings within the cranks, and difficulty in removing the LNER-type casings.
70035–70039 were built with roller bearings on the leading and trailing coupled axles only and plain bearings on the remaining axles, whilst 70040–70049 were built with plain bearings throughout.
However throughout their service the roller bearings used in remaining cases showed no advantage in reliability or cost.

An unusual fault with the first engines of the class was fore-and-aft vibration, strong enough to prompt passengers to complain and to cause fire-irons stowed in a longitudinal compartment on top of the tender to work their way forward into the cab.
The passengers' complaints were dealt with by reducing the tension in the drawbar spring.

Locomotive tenders were also changed as new, improved designs became available.
Some examples of the second batch (70025–70029) were equipped with the BR1A tender, which had a higher water capacity of 5,000 gallons.
Members of the third batch (70045–70054) were equipped with another tender design, the BR1D, which had 9 tons of coal and 4,750 gallons of water, due to the fact that they were intended for use on longer runs in the north of the railway network.
This tender design also featured a steam-powered coal pusher, which eliminated the need for crew members to mount the tender to pull forward coal when the locomotive was at a stop.

Nos.70043 and 70044 were delivered with Westinghouse airbrakes fitted alongside the smokebox and with no smoke deflectors.
The two locomotives, which looked radically different from the rest of the class, were allocated to Manchester (Longsight) and ran a series of brake trials on the London Midland main line during the mid-1950s.
Subsequently, both had the equipment removed and deflectors fitted.

No.
70045 was fitted with LMS-style oval buffers in the course of repairs after collision damage.

On 21 January 1960, the Settle rail crash, which cost the lives of five passengers, was caused when the piston rod, cross-head and connecting rod of No.
70052 came loose and damaged the opposite line as a freight train was approaching.
The locomotive of the freight train was derailed towards 70052's train and tore out the sides of three passenger coaches.
Part of the slide assembly was redesigned, and was fitted as the locomotives were routinely "shopped".

Western Region based examples had hand/foot holds cut into the smoke deflectors replacing the original handrails after a major derailment, to improve forward visibility.
Some of these deflectors subsequently migrated to other members of the class.
Problems with the class were experienced immediately, with the first 25 locomotives being withdrawn in October 1951 after several complaints were received from crews regarding the driving wheels shifting on their axles. They were subsequently modified, and released back into revenue-earning service.  Initially the return cranks on the main driving wheels were of LNER block type, as seen on Arthur Peppercorn's A1s and A2s, but this was changed to the simpler LMS four-stud fitting. This was the result of a problem of overheating bearings within the cranks, and difficulty in removing the LNER-type casings. 70035–70039 were built with roller bearings on the leading and trailing coupled axles only and plain bearings on the remaining axles, whilst 70040–70049 were built with plain bearings throughout. However throughout their service the roller bearings used in remaining cases showed no advantage in reliability or cost.
An unusual fault with the first engines of the class was fore-and-aft vibration, strong enough to prompt passengers to complain and to cause fire-irons stowed in a longitudinal compartment on top of the tender to work their way forward into the cab. The passengers' complaints were dealt with by reducing the tension in the drawbar spring.
Locomotive tenders were also changed as new, improved designs became available. Some examples of the second batch (70025–70029) were equipped with the BR1A tender, which had a higher water capacity of 5,000 gallons. Members of the third batch (70045–70054) were equipped with another tender design, the BR1D, which had 9 tons of coal and 4,750 gallons of water, due to the fact that they were intended for use on longer runs in the north of the railway network. This tender design also featured a steam-powered coal pusher, which eliminated the need for crew members to mount the tender to pull forward coal when the locomotive was at a stop.
Nos.70043 and 70044 were delivered with Westinghouse airbrakes fitted alongside the smokebox and with no smoke deflectors. The two locomotives, which looked radically different from the rest of the class, were allocated to Manchester (Longsight) and ran a series of brake trials on the London Midland main line during the mid-1950s. Subsequently, both had the equipment removed and deflectors fitted.
No. 70045 was fitted with LMS-style oval buffers in the course of repairs after collision damage.
On 21 January 1960, the Settle rail crash, which cost the lives of five passengers, was caused when the piston rod, cross-head and connecting rod of No. 70052 came loose and damaged the opposite line as a freight train was approaching. The locomotive of the freight train was derailed towards 70052's train and tore out the sides of three passenger coaches. Part of the slide assembly was redesigned, and was fitted as the locomotives were routinely "shopped".
Western Region based examples had hand/foot holds cut into the smoke deflectors replacing the original handrails after a major derailment, to improve forward visibility. Some of these deflectors subsequently migrated to other members of the class.
BR Standard Class 7