Accessing the R Cowl Plenum Drain (from exterior)
ETA 6-4-2022. Select front end disassembly documentation appended to end of post.
Removed the R Fender to allow for inspection. R side of Cowl Drain was full of damp debris. Now that I can visually inspect the area behind the Fender, it is clear the R Cowl Drain Outlet is directly above the worst rust I currently observe inside the Cab at the top of what is often called the “Kick Panel” area. The Air Inlet Assembly, which is rear of the Blower Motor is located in the upper portion of the sheet metal enclosure that is the R end of the Cowl Drain. I will likely try to remove the Dash and Air Inlet Assembly later today. I hope I do not break anything, or at least nothing difficult to replace or repair. Intend to update this thread as I disassemble and get a better view of the rust.
So, why do I care about this? The relevant truck is intended to be my next daily driver. I would like to get 200k more miles out of it, and do not want the cab rotting away until I get closer to that goal.
Wide angle view of R front Cab corner with sheet metal removed.
R Cowl Drain Outlet. The black, plastic Cowl Ventilator Tube (water deflector), has been removed for better access.
Partially obstructed view of interior Cab rust below and opposite the R Cowl Drain Outlet. Some seam sealer removed for inspection.
Following information appended 6-4-2022.
R Wheelhouse and Fender Removal.
*Unfortunately, the following must be removed before either Fender can be removed: Radiator Grille; Front Bumper Assembly (complete); and Hood.
I did not document this early parts removal well at all, especially with photos. However, I will include notes and a few photos for the process on my 1996 Sonoma SLS. Some photos are of parts after removal, showing fastener locations. Later portions of the inspection and repair process are better documented in subsequent posts.
Remove Composite Headlamps (x2). Remove rubber or PVC caps for the 2 – long, mounting screws. Remove the 2 – screws (5mm). Disconnect all 3 – lamp holders from Headlamp. Headlamp is now free for removal.
Remove Radiator Grille. Remove Grille to Radiator Support screws: 6 - M4.2-1.41 x 20mm 12mm washer SEM screw (7mm). Carefully pull Grille straight out from vehicle to release the 4 – metal Retainers. The Retainers are mounted on very thin extensions of the Grille that will not withstand much lateral force before breaking.
Remove Front Bumper Assembly (complete). The following can be removed as 1 – assembly: Front Bumper Impact Bar; Bumper Fascia; Park/Turn Lenses; and Radiator Air Deflector. From below vehicle, remove 2 - M10-1.5 x 30mm flanged hex bolt (15mm) connecting outer portion of Bumper to Bumper Brace. While still down there, disconnect lamp holder from each Park/Turn Lamp. From above Bumper remove 4 - M10-1.5 x 35mm button head dog point bolts (T50). Pull Bumper Assembly forward to disengage from locating pins projecting out from Fenders.
Remove Hood. First, remove R & L Cowl Grille Panels. Each is held in place with 1 - M4.2-0.79 x 17mm 12mm washer SEM screw (7mm); metal retainer; and tab interlocking it with the Center Cowl Grille Panel. Remove screw. Carefully lift outer edge to free Retainer, understanding interlocking tab is interlocked with Center Cowl Grille Panel. Pull up and outward to remove. Be careful. It is easy to damage the Center Panel interlocking loop. Disconnect Windshield Washer Hoses from Windshield Washer Nozzles. Be careful. The original Nozzles are NLA and OEM/aftermarket replacements do not fit the original hoses. Disconnect Vacuum Hose from Vacuum Reservoir. Disconnect any Underhood Light wire harness. With Hood propped in the upright position, remove 2 – M8-1.25 hex nut w/ free-spinning 20mm washer (13mm) for Hood Hinges. With a helper, keep Hood upright while lowering Prop Rod; remove 2 – M8-1.25 x 22mm flanged hex shoulder bolt (13mm) for Hood Hinges; and lift Hood off vehicle. I set mine, upside down, on top of the Cab & Cap with towels in between.
Remove R Wheelhouse. First, if battery not already removed, do so now. Disconnect the Battery Cables by loosening the Studs (8mm). Remove 1 - M8-1.25 flanged hex nut (13mm) for the Battery Hold Down and 1 – Battery Hold Down Retainer (rubber). Remove Battery. Remove the 2 - M8-1.25 x 30mm 24mm washer SEM bolts (13mm) for Battery Tray. Remove Battery Tray. Disconnect both Hoses at the Radiator Coolant Recovery Reservoir. Keep the Hose from the Radiator held up or it will dribble Coolant. Remove 3 - M6-1.0 x 16mm 17mm washer SEM screws (10mm) for ECM and support the ECM safely out of the way. Remove 3 - M6-1.0 hex nut w/ free-spinning 18mm washer (10mm) for Engine Coolant Recovery Reservoir and remove Reservoir. From below Wheelhouse, remove Reinforcement at front, bottom of Wheelhouse: 2 – M8-1.25 x 25mm 24mm washer SEM screws (13mm) and 1 – M8-1.25 x 17mm 24mm washer SEM screws (13mm) (closest to Fender). Remove 2 – M8-1.25 x 22mm 32mm washer SEM screws (13mm) for Firewall tabs. Remove final 6 – M8-1.25 x 25mm 24mm washer SEM screws (13mm) for Fender connection. Wheelhouse will wiggle loose and out.
Remove R Fender. First, separate the coaxial Antenna Cable at the connection approximately 6” from the Antenna Base mounted in the Fender. Then, remove 8 – bolts; all M8-1.25 x 30mm 24mm washer SEM (13mm). 2 – bolts at hood hinge location. 2 – bolts at rear edge of Fender, accessible from Cab area through gap between Door and Cab. 1 – bolt at rear, bottom of Fender. 2 – bolts at front, bottom of Fender. 1 – bolt at front, top of Fender. Slip Fender forward, away from Door and remove. 1 – bolt from back of the Radiator Support was previously removed as it was 1 of 2 - bolts that mounted the Battery Tray.
Headlamp mounting screws. Headlamp was temporarily reinstalled to obtain reference photo.
Radiator Grille (front view). Yellow circles show all locations where screws attach Grille to Radiator Support.
Radiator Grille (rear view). Yellow circles show locations of all Retainers.
Bumper (top, rear view). Yellow circles show locations of all mounting bolts.
L Cowl Grille Panel (rear view). Yellow circle shows location of mounting screw. Green circle shows location of Retainer. Red circle shows location of interlocking tab. R Panel is mirror image.