Under the assumption that isospin T is a good quantum number, mirror transitions Tz = + 1 - 0 and Tz = -1 - 0 were studied in A = 34 isobars, where Tz is z component of iospin T and is defined by Tz = (N - Z)/2. With a high energy resolution of 35 ke V in 34 S(He,t)34 Cl reaction measurement at 0o scattering angle and at an incident energy of 140 Me V/nucleon, strengths of Fermi and Gamow-Teller (GT) transitions from the Jn: = 0+, Tz = +1 ground state of 34 S to the Jn: = 1+, Tz = 0 excited states in 34 Cl were determined up to excitation energy (Ex) of 7.08 Me V. The corresponding isospin-symmetric transitions connecting Tz = -1 and Tz = 0 states can be studied in the 34 Ar /3+ decay. The strengths of the (GT)+ or - transitions were compared up to the excitation energy of 3.1 Me V. A good agreement was observed for two strong transitions to 2.580 MeV and 3.129 MeV states, while a disagreement about 45 percent was observed for a weaker transition to 0. 666 Me V low-lying state.