from the Type 3 & 4 Club

There's not much that's worse than sitting in your lovely old VW, turning the key, and ... NOTHING!  It's a very common problem, which often results in being charged for a new starter motor if you entrust the repair to a garage.  Sometimes it may need that, but often it's a much simpler solution than that. Ask yourself these questions:-

Does the motor sometimes work?     Does it sound happy when it does work?  

Does it usually fail after a fast run?     Is the battery as good as it might be?  

Have I undone the wires to the starter motor and cleaned the connections? (IMPORTANT: disconnect the battery first)

If the answer to all these is 'yes', you probably simply need to clean the motor itself.  This is fairly easy!   The reason it causes problems is that the solenoid current has to flow through the motor as well, and the brushes  (B) and commutator get dirty and worn, so not enough current can flow to start the solenoid moving.  This seems to be aggravated by getting hot during a long run, which could be lack of lubrication on the drive pinion.  Of course, changing any part of the system, even cleaning wiring connections etc, may improve the situation for a time.

• disconnect the battery
• remove the starter motor, noting which wires goes where (extra one on some FI cars)
• undo the end cap and long through-bolts, and remove the end cover carefully
• check the brushes are long enough to press firmly on the commutator
• remove the brush plate, carefully removing the brushes as necessary 
• clean the dirty areas on the brushes and commutator (this may need fine sandpaper)
• clean out the slots on the comutator (they should be slightly sunken below the copper segments)
• check the drive pinion operates smoothly (WD40 is good to free it off)
• re-grease the shafts and reassemble the motor parts
• seal the outside against water (I sprayed with Smoothrite and then Waxoyl)
• check the bush in the bell-housing that the motor shaft fits in, and grease it
• re-fit the motor, taking care to tighten nuts, bolts and wires properly.

Enjoy your revitalised starter!