Rear wheel drive helping hand speed change mechanism

The utility model provides a rear wheel drive helping hand speed change mechanism, it relates to a speed change mechanism to solving current trailer tractor and depending merely on front wheel drive, can not guarantee tractor and trailer synchronous operation, especially travel on roping goods slope way, front wheel drive exerts oneself inadequately, draws motionless trailer, and drive nature is not strong, mobility less than the problem, it includes the box, pulls out the fork, dual gea, middle input shaft, middle output shaft, one -level gear and second grade gear, middle input shaft with middle output shaft is the integral key shaft, dual gea, one -level gear and second grade gear have been arranged in the box, middle input shaft with middle output shaft parallel arrangement rotates and installs on the box, dual gea slidable mounting is in on the middle input shaft, the one -level gear with second grade gear interval sets up and solid dress is in on the middle output shaft, install on dual gea's the adapte