the variable speed trigger on my bosch feels sticky and sometimes doesn't start on low speed, just jumps.

Diagnosis

The "jumpy" behavior and physical stickiness in the Bosch GST18V-60CN variable speed trigger are caused by the accumulation of fine particulate matter—specifically a mixture of sawdust, resin, and atmospheric moisture—inside the trigger housing. The variable speed control is managed by a potentiometer (a variable resistor) that translates the physical position of the trigger into a voltage signal for the motor controller. When sawdust penetrates the seams of the plastic housing, it creates a physical obstruction that prevents the trigger from returning to its neutral position smoothly. More critically, the "jumping" effect occurs because the debris has contaminated the conductive tracks of the potentiometer. Instead of a smooth linear increase in voltage, the dust creates "dead spots" or intermittent bridges of conductivity. When you pull the trigger, the tool may not register the initial low-voltage signal, and then suddenly "jump" to a higher speed once the contact finally breaks through the debris layer to hit a conductive strip. You can confirm this by observing if the tool intermittently fails to start at a slow crawl but operates normally once you pull the trigger past the 50% mark.

How to Fix It

To resolve this without a full teardown, you must flush the internal contacts. Follow these precise steps:

1. Remove the 18V battery pack completely to ensure there is no current flowing to the logic board.
2. Use a high-pressure can of non-residue electrical contact cleaner (such as CRC QD Electronic Cleaner or DeoxIT). Do not use WD-40 or silicone sprays, as these leave a film that attracts more dust.
3. Locate the gaps around the trigger assembly. Insert the straw attachment of the cleaner directly into the gap between the trigger and the tool casing, aiming specifically for the pivot point and the rear of the trigger where the potentiometer is located.
4. While spraying, rapidly cycle the trigger from fully closed to fully open 20 to 30 times. This mechanical action scrubs the conductive tracks and flushes out the loosened sawdust.
5. Rotate the tool and repeat the process from the opposite side of the trigger housing to ensure total coverage.
6. Use a can of compressed air to blow out any remaining liquid and loosened debris from the trigger seams.
7. Allow the tool to dry for at least 15 minutes before re-inserting the battery to avoid shorting the electronics.

If That Didn't Work

• Deep Clean via Housing Removal: If the external spray fails, remove the 6-8 Torx screws holding the plastic clamshell together. Carefully lift the housing, avoiding the delicate wires connecting the trigger to the PCB. Use a soft-bristled brush and isopropyl alcohol (90% or higher) to manually scrub the trigger mechanism and the potentiometer contacts before reassembling.
• Trigger Spring Tension Check: Inspect the return spring located at the base of the trigger. If the spring has become fatigued or displaced, the trigger will not seat properly, causing the tool to "stutter" or fail to engage at low speeds. If the spring is kinked, it must be replaced to ensure consistent pressure on the switch.
• Full Switch Module Replacement: If the potentiometer tracks are physically worn through (common in high-use professional environments), the switch is permanently damaged. Replace the entire trigger switch assembly. Ensure you source the genuine Bosch replacement part specific to the GST18V-60CN to maintain the correct variable speed curve.
• Battery Terminal Inspection: Check the battery contact pins for carbon buildup. While less likely to cause "stickiness," oxidized contacts can cause voltage drops that mimic a faulty trigger by causing the motor to surge or jump upon startup. Clean contacts with a fine-grit sanding sponge.

Heads Up

• Avoid Compressed Air Blasting: Never blow compressed air directly into the trigger without first using a cleaner; this often pushes sawdust deeper into the potentiometer, making the problem worse.
• Resin Warning: When cutting resinous woods (like pine), the dust becomes "sticky" when warm. Use the integrated dust extraction or a vacuum to prevent this resin from bonding to the trigger mechanism.
• Storage Tip: Store the tool in a dry environment. High humidity combined with sawdust creates a "paste" inside the switch that can lead to permanent corrosion of the electronic tracks.
• Trigger Discipline: Avoid "feathering" the trigger excessively at the very bottom of the throw for long periods, as this creates the most friction and wear on the lowest part of the potentiometer track.