Hi V.F.
This is a very common problem with self propelled hoovers. Try adjusting the cable running to the transmission lever on top of the transmission.The lever moves right to left.
Put the handle in the cleaning position,lock the handle grip in neutral start the machine with the base off the floor, loosen the cable be careful,its like a jam nut slide the tranny lever back and forth till the transmission is not enguaging either way front or back.The clutches should be in freewheel and not gripping or clamping in either forward or reverse. Tighten the jam nut.If the transmission is enguaging a little either forward or backwards when off the floor this is just cetricial force acting it should stop when on the floor .If the machine is still tugging against you the cable has to be adjusted again.
Oh yeah take the hood off its easier to get thru this way.
Btw when moving the rug and floor selector back and forth make sure the nozzle is of the floor or else the slides or actuator breaks from the pressure.
MOLE