As above; this shaking is usually caused by a broken ball joint on the stabilizer bar on the left hand skid plate. Would suggest that you do not operate the machine until the problem is solved as to do so rapidly destroys the bushes in the parallel arms holding the skid plates. To replace these means a serious bit of work on the front. Other possibilities are that the ball joint mounting on the skid plate has broken out or the kevlar bushes in the stabilizer bar pivot shaft have been destroyed or the mild steel stabilizer pivot shaft is badly worn. Usually both! If replacing the pivot shaft, get a chrome steel shaft made up from hydraulic ram shaft steel. It and the shaft bushes will then last for years. We have been through all of these problems as we normally use our 30 ft 1994 build 500 series flex front over about 1000 acres a year of lentils in flex mode plus the usual other crops with the front locked up in the non flex position. Cheers!