We present a weak-lensing and dynamical study of the complex cluster Abell 1758 ( A1758 , \bar { z } = 0.278 ) supported by hydrodynamical simulations . This cluster is composed of two main structures , called A1758N and A1758S . The Northern structure is composed of A1758NW & A1758NE , with lensing determined masses of 7.90 _ { -1.55 } ^ { +1.89 } \times 10 ^ { 14 } M _ { \odot } and 5.49 _ { -1.33 } ^ { +1.67 } \times 10 ^ { 14 } M _ { \odot } , respectively . They show a remarkable feature : while in A1758NW there is a spatial agreement among weak lensing mass distribution , intracluster medium and its brightest cluster galaxy ( BCG ) in A1758NE the X-ray peak is located 96 _ { -15 } ^ { +14 } arcsec away from the mass peak and BCG positions . Given the detachment between gas and mass we could use the local surface mass density to estimate an upper limit for the dark matter self-interaction cross section : \sigma / m < 5.83 cm ^ { 2 } g ^ { -1 } . Combining our velocity data with hydrodynamical simulations we have shown that A1758 NW & NE had their closest approach 0.27 Gyr ago and their merger axis is 21 \pm 12 degrees from the plane of the sky . In the A1758S system we have measured a total mass of 4.96 _ { -1.19 } ^ { +1.08 } \times 10 ^ { 14 } M _ { \odot } and , using radial velocity data , we found that the main merger axis is located at 70 \pm 4 degrees from the plane of the sky , therefore closest to the line-of-sight .