86 560sel rear shocks and accumulators

my 86 560sel has a hard thump noise in the rear every time you hit a bump. the accumulators were changed but the problem is still there. is there any special trick to installing these accumulators because the mechanic was not to expereinced with this system. i dont want to just go and replace the shocks because the price of these units are astronomical. is there any other remedy to soften the shock. thanks