Designed in late 1925, the 1926 Lea-Francis range saw a number of modifications being made to the chassis design. The newly designated J, K, L, M and N types kept the quarter elliptic rear springs, hand-brake operating on the transmission and cone clutch of the earlier models, but with improvements such as stiffer rear cross-members and improved rear spring mounting. All models, except the G Type, now came with four wheel brakes as standard.
Fitted with the Meadows 4EC engine the chassis was classified the J Type and designated as the standard 12hp model. More J Types were built than any other single model of car at the Lower Ford Street works. Only the post war 14hp saloon was made in higher numbers.
Bodies for the J type were Avon four seaters with two seaters and coupes by Cross and Ellis. A few saloons were fitted by Vulcan and one or two bodies by Midland Motor Body Co.