Battery & Volt Drop – Test Procedure
The most critical and overlooked component when fault finding Starter motors and Alternators.
The Battery should always be checked first, and then wiring for voltage drops.
If the battery is not a 100% charged and capable of maintaining its charge, the electrical system will eventually fail, leading to Alternator and Starter motor failure and possible damage.
Use a Volt meter to test the Battery.
Battery condition:
| 12.6 Volts | a fully charged battery 100% |
| 12.4 Volts | 75% |
| 12.2 Volts | 50% |
| 12.0 Volts | 25% |
| 11.8 Volts | 0% |
Starter Motor Diagram & Tests & Common Problems
A complete guide on Starter Motors including below information:
- Exploded Diagram of a Starter Motor
- Starter Motor installation guide
- Starter Motor pre-installation check (Summary)
- System Checks
- Common General Starter Motor Faults ( Summary)
- Starter Motor trouble shooting guide
- Burnt out Starter Motors
- How to test a Starter Motor voltage drop
- Different Teeth on pinion for same application
- With & without a bracket
- Noise & Dowel movement
- VW starters with axel and bulbous types
- Pal Magneton vs Lucas M50 types
- Starter Motor brush replacement instructions
- OE Part number location
Mercedes A Class Starter motor – Technical update
There are 4 different starter motors for the Merc A Class, the problem occurs on the 8 Tooth and 10 Tooth versions.
Starter Motor Pre-installation check:
- 65% of all starter failure due to a faulty or weak battery (batteries should be replaced every 3 years with the required correct cold cranking amps) and over cranking of the unit.
- 20% of all starter failure is due to poor electrical connections, fuseable links, bad battery cables and bad grounds. Cables can be tested by verifying that the voltage drop doesn’t exceed ½ volt from end to end.
- 8% of all starter failure is due to improperly mounted starters (Dowel mounting/loose bolts).
- 7% of all starter failure is due to improper timing and overheating
Note: Before installing a starter motor you must be certain of a fully charged battery.
Common General Starter Motor Faults:
- Clicks only:
- Poor wiring connections.
- Defective solenoid.
- Defective ignition switch.
- Defective Starter Motor.
- Poor earth connection.
- Turns slowly:
- Poor battery condition.
- Poor wiring connections.
- Corroded battery cables.
- Generally worn Starter Motor.
- Running in mesh:
- Defective ignition switch.
- Sticking solenoid.
- Sticking pinion.
- Noisy in operation:
- Loose mountings.
- Locating dowel (if applicable) not fitted, or fitted askew.
- Ring gear damage (although this is extremely rare the ring gear is made of hardened steel and the drive pinion is made of mild steel
- Defective pinion
ZEN – useful information on starter motors
How to measure Pinion Diameter
How to identify Pinion Rotation
How to replace a Starter drive on a stop Spline system
