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How to modify a NBS ext cab with rear bench for 40/60 seats

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How to modify a NBS ext cab with rear bench for 40/60 seats

Postby alkalore [OP] » Apr 18 2017, 5:44am

Subject: How to modify a NBS with an extended cab with a stock rear bench seat to accept 40/60 split rear seats
The scope of this how-to is limited to the modifications required for a 40/60 split rear bench seat to be installed in a NBS truck that has a stock bench seat. Seat removal and installation is not covered.

The goal of this how-to is to describe the steps necessary to allow installation of a 40/60 split rear seat in a NBS extended cab that came stock with a single bench seat. For me the motivation was that I purchased my truck used, and the previous owner kindly removed the rear seat. I wanted to go leather and I found a 40/60 OEM leather rear seat from https://www.oemcarandtruckseats.com/. I wasn't sure exactly how these seats would be installed, but was confident it would be simple. After I performed a fit check I was a bit confused. While the rear passenger seat had all four mounting location identified, it wasn't clear how the driver side would mount at the inner bracket as there were no stud locations in the floor. With a bit more hunting I realized that the driver side actually mounts to the passenger side bracket using two M8-1.25x25mm fasteners. At any rate, my motivation for putting this how-to together is to help anyone else wanting (or forced) to do this swap. Enjoy - it's a quick one!

    Skill Level: Anyone
    Time: 1-2 hrs
    Required Tools & consumables: M12-1.75 tap, 10.2mm drill bit, (or 7/16 inch), lubricant, flat head screw driver, utility knife
    Required Hardware: Qty 2, M12-1.75x50mm bolts
    Assumptions: You must know how to remove your stock rear seat and gain access to the trucks floor (complete or partial removal of the carpet and insulation).

Step 1: Remove rear seat assembly and expose the floor forward of the middle stud (OEM stud nearest note D).
Step 2: Locate and remove the two plastic plugs which cover the mounting location for the passenger side seat and seat buckle. See note A. I found a flat-head screw driver worked best for this. At first I thought these mounting holes were already tapped, but in my 2011 they were unfortunately not.
Step 3: Clean up minor diameter of hole and thread using a M12-1.75 tap. The holes were a bit corroded, so I used a 7/16 drill to cleanup the holes. I used a slightly larger drill for my M12 tap because it wasn't high quality and I was concerned it would snap off. Please advise: Be cautious here and use lubricant and a quality tap. You don't want to remove a broken HSS tap.
Step 4: You have some choices here. I opted to use two M12-1.75x50mm fasteners and threaded them from the underside so they can be used as studs like the rest. You could optionally bolt the seat and buckle. The photo below shows the finished installation with annotations.
Step 5 (Optional): I chose to seal the underside with a black epoxy paint to reduce corrosion of the fasteners and I used black RTV to seal the periphery (interior side) of each newly installed stud.

I hope this quick write-up helps someone else trying to make this modification. It took me a considerable amount of time searching on this forum to find out that no one has documented how a 40/60 split rear seat gets installed. Now it's here.
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Joined: Oct 29 2014, 9:52pm
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Year: 2006
Make/Model: GMC Sierra
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