Tech Tip: Converting to a Gear Reduction Starting Motor

When converting from a straight drive starting motor to a gear reduction starting motor, there are three points you should focus on to ensure a clean Transition:
  • Design
  • OE spacer
  • Integrated Magnetic Switch (IMS) relay

A gear reduction starter may appear different by design. For example, the Delco Remy 29MT™, 35MT™, 38MT™and 39MT™ all incorporate a nose-less design and don’t include a cone around the starter drive. Despite this design difference, these starters are completely interchangeable with straight drive nose style starters.

Keep in mind, though, that some gear reduction starters, like the Delco Remy 44MT™, do have nose cones.

OE Spacer

The OE spacer—which is actually part of the engine—is designed to ensure proper clearance between the starter pinion gear and the engine ring gear.

If an OE spacer is currently being used, then you’ll need to transfer it with the new replacement starter. This is important because, failure to do so, will likely result in damage to the starter pinion gear and engine ring gear teeth.

During removal of the starter, it’s not uncommon for the OE spacer to stick to the old starter. It’s always good practice to check if the spacer is attached to the old starter nose housing before you begin.

Finally, if you are unsure if the engine requires an OE spacer—or if it’s damaged or lost—we recommend you contact the engine manufacturer for Details.


Integrated Magnetic Switch Relay

The final point is the Integrated Magnetic Switch (IMS) relay. The IMS reduces voltage drop and controls battery current to ensure the solenoid receives the maximum available voltage in any starting condition.

If the replacement gear reduction starter already has an IMS attached to the unit, then you need to leave the IMS on the new starter. You should never remove or uninstall it. Removal of the IMS may result in control circuit problems and will void your warranty.

However, the unit you are replacing may have an external magnetic switch already mounted on the vehicle’s firewall. If that’s the case, you have two options:

illustration1Option 1
Bypass the firewall magnetic switch and connect the ignition wire directly to the starter-supplied IMS (see illustration 1).

illustration-2Option 2
Connect the switch wire from the firewall-mounted magnetic switch that goes to the starter motor solenoid switch terminal and reconnect to the starter-mounted IMS. (see illustration 2).

On the Delco Remy 29MT, 38MT and 39MT models, it is strongly recommended that you have the IMS equipped during installation. On the 35MT and 44MT models, the IMS is integrated into the solenoid so these starters will not have the IMS attached to the motor.

web-installationYou can visit and click on the Product Support tab to download instruction sheets for installation procedures and alternate switch position locations.

Technical Support Center +1 800 3720222

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