911 Rear Shoulder Seat Belt Conversion
 


I am doing my best to make the rear seats of my 911 useful for kid hauling. Fortunately, I have a 1986 911. These models have the built in mounting points for belts that never made it to US shores until > 1987. SO after checking my own car for buried mounts, I ordered a set of used shoulder belts from LA Porsche Dismantlers for $200, and have finally gotten to work.


Parts List:

  • Belts

    Tools:

    • Tape measures and rulers (measure twice cut once!!)
    • Philips Head Screwdriver
    • 17 MM Socket Set
    • XActo Pen Knife
    • XActo wood working kit - flat blade bit mounted to handle
    • Power drill, 1/16" and 1/4" bits, Philips head driver
    • Coping Saw
    • Small shop vacuum
    • Hand files - flat and round

    Materials:

    • Cardboard for a template, large piece.
    • Pen

    Procedures

    Mounting the 3 Point Shoulder Seatbelts

    Early Work Adding a LATCH top tether to my 911

    In addition to shoulder belts, having solid mounting points for baby seats is a really nice addition to the project. Some images inspired by recent efforts on the Pelican Parts Tech Forums

    After way too much thought, I went about a web search looking for seatbelt and harness hardware.

    Here was the solution, a kit used to configure Shroth aftermarket harnesses. a kit "SR01324" used to install Shroth aftermarked auto harnesses The adapter is indended for belt OR for clip in belt connector use.

    Cutting Holes and Installing Belt Guides In A 911's Rear Deck

    Once the parts were finally collected the together and the new Shroth mounts looked like a go, I got to work very rapidly.

    Building a Template for the Rear DeckThe first critical step to doing this right was to build a cardboard template of the rear deck. In this process, I learned that I actually needed the standard Porsche belt guide as opposed to any funky periscope trims, and that the mounting surface would be relatively flat despite the curves of the deck.

    1. Remove Deck from Car.
    2. Trace the lower part of the deck onto a large piece of cardboard.
    3. TRACE the 4 screw holes
    4. Cut out the tracing.
    5. Mount the cut cardboard template to the ORIGINAL deck to check for final sizing.
    6. And the final step, MOUNT the TEMPLATE in the CAR using the original 4 bolts that hold the deck. Of all the pictures I took, I failed to take one of this setup. I ended up driving around for 2 weeks with my cardboard deck as I waited for my parts and time to proceed further, freaking out the 911 fans at my office when they saw it!
    Cutting Holes in the Rear Deck

    Step 1P1010016.jpg
    The 911 rear deck, removed from the car, speakers removed as well.
    Step 2P1010017.jpg
    The Shroth harness mount using the belt retractor bolt.
    Step 3P1010018.jpg
    I poked a hole in the cardboard template using the Shroth harness lined up where the top trim piece would need to go. I then removed the cardboard deck template from the car by removing the 4 screws holding it in place
    Step 4P1010019.jpg
    As an option, I *could* have cut one square hole. As it turns out, the rear deck material is VERY thick and strong enough to support 2 guide holes this close.
    Step 5P1010020.jpg
    I mirrored the template, tracing the left side (facing the deck) guide holes onto the right side by folding the template in half. I had a very good template to "trust the symmetry", don't go freehanding on your 911!!
    Step 6P1010021.jpg
    Confirming the guide hole tracings on the left side using the actual guides. The guides are also fit to the cardboard template to determine the guide mount holes. Cut out the holes left and right side.
    Step 7P1010022.jpg
    Mounting the template deck TO the actual deck, and then trace the template holes (guide and drill holes) to the actual deck using a non-permanent pen. Do the right and left side both, check symmetry with a RULER.
    Step 8P1010023.jpg
    Remove the template to reveal where the holes will be cut into the real deck.
    Step 9P1010024.jpg
    Drilling out the guide mount holes with a small bit. I quickly realized the deck had a lot of padding between the cover and the actual backing.
    Step 10P1010025.jpg
    Not shown is the very sharp XActo pen knife that sliced the cover vinyl like butter. The pad material underneath was not so easily removed. I pulled out a flat scrapper blade from my XActo wood working kit to shave the foam off the solid backing surface.
    Step 11P1010026.jpg
    The guides in the holes recessed about 5-7 mm to the solid backing below. The top cover material and foam displayed for reference.
    Step 12P1010027.jpg
    With a large bit - 1/4" or so, drill holes at each corner of the guide holes. I was impressed how deep the material was, and how many shavings were generated. Shop vac time!
    Step 13P1010028.jpg
    The coping saw. Who said 7th grade shop would never be useful? The material cut very rapidly compared to the butternut hardwood I "coped" into a maple leaf in said shop class.
    Step 14P1010029.jpg
    More coping saw, with cut away (literally a cut away) showing the depth of the solid base material. Using flat and round files may be necessary to get the guides to fit after the cutting steps.
    Step 15P1010030.jpg
    Two guide holes cut with guides inserted! I made a small error during "Step 3" - the guides are NOT symmetrical across their axis between the mount holes. I was only able to squeeze them together by having them "back to back", exposing the "slot" outward (boo!).
    Step 16P1010031.jpg
    Check and re-drill out the mounting holes. Screw in the guides with a Phillips driver using the official Porsche Guide Screws from Pelican.
    Step 17P1010032.jpg
    Repeat Steps 7 to 16 on the right side. Put the speakers back in the deck and get ready to head out to the car.
    Step 18P1010033.jpg
    Reconnect the speaker wires, feed the belt end and belt connector through the TOP guide holes on both sides. Make sure the tether mount is reachable, tighten down bolts with your 17mm. The right side shown works!
    Step 19P1010034.jpg
    Check it out! Zoom of the left sideshowing the guides, the new belt, the tether mount and the seat retaining strap leather.
    Step 20P1010035.jpg
    Both rear seats with shoulder belts. Note in the foreground the front belt guide is identical to the rears! Also, note the rain in California - cold as heck too last night!
    Step 21P1010036.jpg
    Trying out the tether mount using an older gen (2001) Britax Roundabout in the FRONT seat. The seat is VERY solidly mounted now. I imagine harnesses could be used in similar fashion, but what I now need is the perfect child/booster seat to use these rear seats and 3 point belts.

    Conclusion

    So it works well and looks pretty good. I am ready to add extra mounts for more LATCH connectors at the rear seat belt mount point. I am also looking for "the ultimate" rear booster seat for a 911 - narrow in the back and very shallow - suggestions please.

    Cosco Tote 'n GoNO! This seat requires lap belts mounted close to the seat back, not the case with a 911 rear belt.
    Britax Starriser Comfy - Works WellThis booster fits well - I still put a towel under it, but my son loves it.
    P1010014.jpg

    References