Planetary Gear Systems have been around for awhile. A very common use for them are automatic transmissions. The gear ratios can be changed by changing the drive gear and the gear that is being driven. There is always one of these 3 gears that has to be fixed.
This Delco 38 MT starter pictured is used to start a 2007 C2 School Bus. You can see the blown planetary gear-set. Quite similar to a transmission planetary failure.. This is common since starters are placed low in the engine and exposed to all sorts of the road elements.
Starters have come a long way and now most are using a planetary gear reduction with more torque delivered for cranking over high compression diesel engines. The Delco 38MT on our Mercedes MBE 900 Diesel engines does the job even with it’s light weight. These starters pack a punch and are light weight with mostly aluminum castings.
The planetary gear system on this starter has a gear reduction of 3 1/2 : 1 ratio which slows down the output of the drive gear (3 1/2 revolutions of the starter motor to 1 revolution of the output drive gear). What this accomplishes is a high torque output that enables the smaller starter motor to punch out the turning force required to crank over the engine.
