SU Pump Quick Repair
SU electric pumps are generally very reliable but after a long period of use they may become erratic stopping occasionally until given a sharp bang. This is caused by burning of the points which prevents current flowing through them and the bang shakes them enough to restore a temporary contact. If they are not burned too badly they can be cleaned up without removing the pump from the car and this will normally provide a get you home solution.
First make sure that ignition is turned off, remove the live wire from the front of the pump and the nut holding the cover in place and lift away the cover to expose the points. Slacken the small screw securing the fixed contact point in place and lift it out (don't drop it!). This contact point can now be cleaned up against an oil stone, a strip of emery cloth or similar.
The moveable contact point is hidden behind the plastic pedestal and to gain access it is necessary to undo the two screws holding the pedestal to the pump base and to pull the top of the pedestal forward and down so that it pivots about the pin which holds the bottom of the moveable contact point to it. You will probably want to remove the screws completely to prevent them falling on the floor. Note where the washers and pigtail earth wire fit under the screw heads. The contact point can now be cleaned up as before. It is best to hold the contact with one hand to prevent it moving about while being cleaned. Do not remove more metal from either of the contacts than necessary. Finally clean the points of any oil and dust, pivot the pedestal back up, replace the screws and the fixed contact point and reconnect the live wire. For the moment leave the cover off and turn on the ignition for a few moments and check if the pump now works. Do not run the pump for long or the pivot pin may vibrate out. If it works replace the cover and the job is done. If it does not work try pressing gently on the fixed point to move it closer to the moveable point. If the pump now works all the time the point is being pressed but stops when the pressure is removed then the gap between the points is now too large. A temporary fix is to bend over the top of the fixed point a little thus closing the gap to the other point. This should be sufficient to get you home and may even work for considerably longer but it is no more than a temporary fix and the points should be replaced as soon as possible as they are no longer parallel and making full face contact.
If the points need to be replaced a new diaphragm should be fitted at the same time as these too have a finite life.