What size speakers are in a 1990 GMC Sierra?
Front-door speakers are typically 4x6 inches, with rear speakers usually the same size; options and variations existed depending on trim and package. Verify your exact setup by measuring or checking your vehicle’s documentation, as configurations can differ.
This article explores the standard factory sizes you’d most commonly encounter in a 1990 GMC Sierra, notes possible variations by trim or cab configuration, and offers guidance on replacement and verification so you can plan upgrades or repairs with confidence.
Factory speaker sizes by area
Common factory layouts for the GMT400-based Sierra around 1990 are summarized below. Keep in mind that exceptions exist based on trim, cab style (regular vs extended), and optional audio packages.
- Front doors: typically 4x6 inches as the standard factory size. Some early or special packages may have used 5.25-inch speakers in the front door area.
- Rear area: when equipped with rear speakers, the standard factory size is usually 4x6 inches. Some configurations or upgrades could differ, but 4x6 is the most commonly cited size for rear playback in these trucks.
In short, the most common factory sizes for the 1990 Sierra center on 4x6 inch speakers in both front and rear locations, with occasional deviations tied to specific trim or options.
Common upgrade options for replacements
When upgrading or replacing the factory speakers, these sizes and approaches are frequently used by owners and installers. Start with the simplest upgrades and consider mounting depth and grill clearance.
- Front doors: replace with 4x6" two-way (or three-way) speakers for a straightforward upgrade. If you want more bass, 5.25" units can often be fitted with appropriate adapters, subject to depth and mounting constraints.
- Rear area: replace with 4x6" two-way speakers where space allows; some setups may accommodate larger formats (such as 6x9") only with significant modifications or custom mounting brackets.
When upgrading, ensure you have the correct adapters, wiring pigtails, and enough mounting depth to avoid rubbing against window mechanisms or panels. Always verify fitment against your exact cab style and option package.
How to verify the exact size for your truck
To confirm the precise speaker sizes on your 1990 GMC Sierra, use the following steps. They help account for variances in trim and production run.
- Remove the door panel or rear speaker grille to expose the mounting area, then measure the diameter of the speaker opening using a ruler or caliper.
- Check the speaker mounting depth and available space behind the panel to ensure the replacement won’t hit window hardware or wiring.
- Consult the vehicle’s build sheet or a factory service manual for the exact specifications tied to your VIN and trim level.
- Cross-check the size with a reputable parts catalog or a local retailer by entering your year/model and noting the door or rear speaker location.
If you don’t have direct access to manuals, visiting a dedicated GMT400 parts forum or a professional installer can quickly confirm the correct sizes for your exact trunk/cab configuration.
Summary
The 1990 GMC Sierra typically used 4x6 inch speakers in both front doors and rear areas when equipped with speakers, with occasional variations depending on trim or optional audio packages. For upgrades, 4x6" two-way speakers are the standard starting point, while larger formats may be possible with adapters and depth considerations. Always verify by measuring or consulting documentation to ensure a proper fit for your particular truck.
