Starter wont stop

[south280]

Hi all,  when starting my 1968 280 sl the car cranks but when I turn the key "off" the car keeps cranking or trying to start for about 5-10 seconds after.  What is the cause of this?  do I need a new starter?  Thanks, David

[Tyler S]

A bad starter solenoid is a possibility. The contacts can temporarily weld themselves together.
You will need to check for voltage on the small screw at the terminal block mounted to the side of the oil pan on the passenger side of the car. Have a helper turn the ignition to crank and watch for 12volts. Then have them let go of the key. Voltage should immediately drop to zero. If it drops to zero then start suspecting the starter as the fault. If you continue to get voltage for those 5-10 seconds then start looking elsewhere such as wiring or the ignition switch.

[ja17]

Seen this before and is usually the starter solenoid as Tyler suggests.

[south280]

Hi,  Is it possible to replace just the starter solenoid or do I have to replace the whole starter?  Thanks, David

[Tyler S]

The solenoid can be replaced separately but the entire starter will still need to be removed. The cost savings will be negligible. Also if the starter motor itself is drawing too many amps you may run into the same problem.
A Bosch rebuilt  starter assembly with solenoid runs around $150 and has a warranty.

[wwheeler]

If you have the original starter, the newer ones are smaller, lighter and spin faster than the old ones. Another benefit of changing the starter and solenoid.