2018 Chevrolet Silverado 1500 Transmission & Axle Gear Ratios
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Transmission gear ratios
The 2018 Chevrolet Silverado 1500 offered a variety of transmission options to suit different needs, from fuel efficiency to heavy-duty towing. The most common transmissions were the 6-speed automatic (6L80) and the 8-speed automatic (8L90), with a 10-speed automatic (10L80) introduced late in the model year on some high-trim models. Below are the gear ratios for each:
6-speed Automatic (6L80)
| Gear | Ratio |
|---|---|
| 1st | 4.03 |
| 2nd | 2.36 |
| 3rd | 1.53 |
| 4th | 1.15 |
| 5th | 0.85 |
| 6th | 0.67 |
| Reverse | 3.06 |
8-speed Automatic (8L90)
| Gear | Ratio |
|---|---|
| 1st | 4.56 |
| 2nd | 2.97 |
| 3rd | 2.08 |
| 4th | 1.69 |
| 5th | 1.27 |
| 6th | 1.00 |
| 7th | 0.85 |
| 8th | 0.65 |
| Reverse | 3.82 |
10-speed Automatic (10L80)
| Gear | Ratio |
|---|---|
| 1st | 4.70 |
| 2nd | 2.99 |
| 3rd | 2.15 |
| 4th | 1.80 |
| 5th | 1.52 |
| 6th | 1.28 |
| 7th | 1.00 |
| 8th | 0.85 |
| 9th | 0.69 |
| 10th | 0.63 |
| Reverse | 4.87 |
Available axle ratios
The axle ratio in your Silverado 1500 plays a crucial role in balancing performance, towing capability, and fuel economy. Below are the common axle ratios available for the 2018 model year:
| Ratio | Available With (engine/trim/package) | RPO/Axle Code | Best For |
|---|---|---|---|
| 2.83 | 4.3L V6 (eAssist) | (specific to eAssist) | Fuel Economy |
| 3.08 | 4.3L V6, 5.3L V8 (standard on many trims) | GU4 | Fuel Economy |
| 3.23 | 5.3L V8 (often with Max Trailering Package, or LTZ, High Country) | GU5 | Balanced/Light Towing |
| 3.42 | 5.3L V8, 6.2L V8 (standard with 6.2L V8, part of Max Trailering) | GU6 | Balanced/Good Towing |
| 3.73 | Not commonly offered from factory on 1500, but some specific option/packages for enhanced towing may have offered it in limited capacity. More common on 2500HD. | (Varies) | Heavy Towing |
How to identify your axle ratio
For General Motors vehicles like the Chevrolet Silverado, the easiest way to identify your axle ratio (and other important options) is by checking the RPO (Regular Production Option) sticker. This sticker is typically found in the glove box on the underside of the lid. Look for a three-digit code that starts with "GU" followed by a number such as GU4, GU5, or GU6. These codes correspond to the axle ratios listed above.
Alternatively, you can use a VIN decoder service online, or in some cases, the axle itself may have a tag attached to one of the differential cover bolts, though this is less common on modern light-duty trucks.
Towing vs MPG impact
The axle ratio has a direct and significant impact on both your truck's towing capability and its fuel efficiency. Here
More specs for the 2018 Chevrolet Silverado 1500
Oil Capacity & Filter
Capacity, weight, filter PN, drain plug torque, change interval.
Fluid Type Specs
Engine oil, coolant, ATF, diff, brake, PS, DEF — with OEM spec numbers.
Coolant Capacity & Type
Total system capacity, OEM coolant spec, flush interval, bleed tips.
Transmission Fluid & Service
Trans model, fluid spec, capacity, filter PN, service interval.
Torque Specifications
Lug nuts, drain plug, caliper, axle nut, plug, key fasteners.
Brake Pad & Rotor Specs
Pad PNs, rotor size, min thickness, caliper torque.
Tire Size & Pressure
OEM size, cold psi, bolt pattern, wheel size, TPMS.
Battery Size & Group
Group size, CCA, AGM/flooded, dimensions, reset note.
A/C Refrigerant & Oil
R-134a or R-1234yf, charge oz, PAG oil spec.
Bulb Sizes (Headlight, Tail, Fog)
Headlight, fog, tail, turn, reverse, interior.
Factory Maintenance Schedule
Service intervals by mileage, severe-duty notes, known issues.
Towing Capacity & Payload
Max tow, payload, GVWR/GCWR, hitch class by trim.
Fuse Box Diagram & Amperage
Fuse box locations, layout, amps, and what each fuse controls.
Serpentine Belt Routing & Length
Belt routing, length, rib count, OEM + aftermarket PNs.
Wheel Alignment Specifications
Camber, caster, toe ranges (front & rear), adjustability notes.
Paint Color Codes
All factory colors with paint codes, sticker location, touch-up tips.
Wiper Blade Sizes
Driver/passenger/rear blade size, attachment, OEM + cross-refs.
Spark Plug Type & Gap
Plug PN, gap, torque, interval by engine.
Key Fob Programming
DIY programming steps, FCC ID, fob PN, battery, transponder.
Same spec — other model years
2014 Silverado 1500
2015 Silverado 1500
2016 Silverado 1500
2017 Silverado 1500
2019 Silverado 1500
2020 Silverado 1500
Maintenance & repair guides
2018 Chevrolet Silverado 1500 Maintenance Schedule →
Available maintenance guidance; confirm the manufacturer schedule.
Repair planning references →
Plan the scope of work; detailed procedures need configuration-matched evidence.
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