Parallel shafting gearbox have problems like the frictional losses, gear shifting is very hard under load, wear and tear of gears while shifting and operating of the gears, load distribution on single driven gear and it is hard to derive large reductions gear ratio easily. Present invention introduces a gearbox as a solution for above problems using PGTU (planetary gear trains unit)s such that all the PGTUs in gear box are connected serially with axles on which planetary gears are mounted, of the PGTUs which are arranged between them, forming a series of CPCAs, for transmission from rotating driving shaft on which sun gears are mounted to the driven shaft by braking the motion of the ring gear of PGTU through which the transmission is to be carried out while setting free the ring gears of rest of the PGTUs in the gear box, It is useful in automobile vehicle etc.