My dad was towing his caravan in his N Reg 2.016V 80K Cav, when accelerating up hill at about 40mph, the car stopped accelerating, the autobox was described as feeling lumpy, and the rev counter shot up without any engine rev noise. This happened again and it seems at a particular power/torque level the gearbox stops transmitting power to the wheels. Also a faint hot smell. Any suggestions, is it likely to be terminal since the car is not worth a lot. Any help greatly appreciated.