Side Glazing Layout on Recent GMC Sierra Pickups
Truck owners frequently call me looking for a stationary rear quarter window on this truck, but the cab layout does not actually use fixed quarter glass or rear quarter vents. General Motors phased out true rear quarter glass when the older extended cabs with rear-hinged doors were retired after 2013; today's T1XX body architecture relies solely on full-drop side door windows. What many drivers describe as a rear quarter pane is the rear passenger door glass, bordered forward by the central B-pillar frame run and rearward directly by the door perimeter without any intermediate division bar.
Because there is no glued-in quarter panel, the replacement work centers entirely around a mechanical drop glass held by bottom clamping brackets attached to an electric cable-driven window regulator (such as GM assembly 86818091 for the left side). I stock replacement glass suited to both standard cab dimensions, making it straightforward to reach your location roughly an hour after you get on my schedule to swap out the broken panel. The glass rides within a continuous perimeter rubber run channel weatherstrip (OEM 84729898) rather than an encapsulated urethane bed, requiring proper seating between the inner door sweep and outer beltline moulding to eliminate wind rush.
Crew Cab versus Double Cab Rear Door Dimensions
Matching the correct replacement glass requires distinguishing whether your Sierra is a Crew Cab or an extended-wheelbase Double Cab. Double Cabs utilize visibly narrower rear doors with a shorter track stroke, whereas Crew Cabs feature full-length passenger doors. The glass blanks are not interchangeable between the two body configurations, and the factory glass also varies by transparency level depending on whether the truck came from a fleet baseline or an upgraded consumer trim level.
| Cab Configuration | Door Position | OEM Reference Example | Glass Characteristics |
|---|---|---|---|
| Crew Cab | Rear Left | 85013703 (replaces 86543110) | Full drop, deep-tint tempered safety glass |
| Crew Cab | Rear Right | 86532736 | Full drop, deep-tint tempered safety glass |
| Double Cab | Rear Side | 84560286 (fleet base) | Short-frame drop, standard solar green tint |
Work Truck (WT) builds often use the non-tinted solar green version, while SLE, Elevation, SLT, AT4, and Denali packages come equipped with deep-tint factory privacy glass. Neither version integrates defroster grids, rain sensors, or embedded antennas—those elements are confined to the windshield and back glass.
Distinguishing Side Window Issues from Cab Seam Leaks
When drivers discover pooled water along the rear carpets or the door sill plates, they often suspect the rear side glass seal has failed. In my diagnostic inspections of these trucks, water tracking along the rear interior trim rarely originates at the side door run channel. The T1XX cab structure has a documented tendency for moisture intrusion at the top roof seam near the back glass frame sealant or through deteriorating foam gaskets around the cab-mounted high third brake light. Water enters at the upper roofline, runs down the hidden C-pillar cavities, and surfaces around the rear door sweeps, mimicking a window seal defect.
If the side glass itself is shattered or off-track, the failure is purely mechanical. Road debris strikes or forced entry easily break the tempered safety pane, which crumbles into blunt granules throughout the lower door shell. Cleaning out those bottom pockets, inspecting the regulator lift plate, and aligning the fresh aftermarket pane into the factory rubber run channel restores full weather tightness and eliminates high-speed cabin buffeting.
