My better half won't ride in a car without modern seat belts so I bought new belts from a company that I have been happy with in my last project: Wesco Performance. https://www.wescoperformance.com/replac ... -help.html
As I did with the rear seats in my last project I chose their retractable roadster style belts.
The '74 originally had lap belts only, retractable with the box bolted under the seat. A heavy bracket turned the belt from horizontal to vertical and pointed towards the seat. The old belts had some age on them and who knows if the electrical lock trigger works so all that gets taken out. I found a threaded mounting hole behind the rear seat (is that actually for passengers?) and all I had to do was fabricate a bracket to get the self-locking box in a suitable location.
Here's pictures of the bracket mounted. Passenger side:
I paid a visit to my local You-pick junk yard and found these belt positioners off a 4th Generation Chevy Camaro. They are some kind of super strong plastic and I found a nice meaty spot on the Fiat seat frame to screw these into.
Most belt manufacturers caution against mounting the shoulder belt or harness significantly below the horizontal position of the driver or passenger. In a collision using your installation, the forward energy of the body translates into a considerable compression force on the spine. This is why you see OE installations on the side pillar, above the height of the shoulder.
Yadkin wrote:Hence the belt positioner at the top of the seat. Luckily the factory seat is well-built and has plenty of steel up there.
You will find plenty of posts here about how weak the factory seat frames are with the term Gangsta Lean being quite commonly used in describing it. The seat backs are known to twist and buckle eventually if you regularly turn to look back while reversing instead of using the mirrors. The OEM seating positions in the Spider spec out for a 150 lb driver and a 150 lb passenger.
Yadkin wrote:It would take several multiples of my 170# weight to deform that seat back vertically, to the point of being a problem.
Its still is a well known weakness on the 124 Spider. The seat backs are not as sturdy as you may think they are and their weakness is a pain point that has troubled a great many folks.
In an accident you will get many times your body weight trying to deform the seat backs and rear end collision crash testing showed a tendency for the seats to fold back. The spec on the 124 Spider is only for a 150 lb driver and a 150 lb passenger so you are already over.
For those (like me) who are not skilled at metal fabrication, but want 3 point belt systems, there is a (somewhat) factory based solution available. If you look closely at Yadkin's pix #3 and #4, one can make out a small circular cap on the plastic inner liner. Behind that cap is a factory installed threaded receptacle for the non retracting shoulder belts used in the Euro versions of the early/mid-70's Spiders. The shoulder belts were clearly illustrated in my original manual (but not in the North American insert, which accompanied it). I also recalled that my sadly missed 71 Coupe had a 3 point system installed by the PO, with the shoulder belt anchors in roughly the same position. The factory welded receivers accept the standard mounting bolts for seatbelts.
I needed the folks at Seatbeltplanet to custom adapt a retractor which would work in any orientation (not just vertical, as most do). Since I purchased mine, I believe Sbp now has a specific model for Spiders. I needed to cut away some of the plastic liner for the retractor to clear and swivel, but it works, even with the air deflector in place. Using A/R's metal shoulder belt guides to feed the belt over the seat.
This elevates the anchor point for the shoulder belt by about 6-8 inches, but still not horizontal. It's worked for me and Patty so far. Just another approach for folks to consider.
Neil
Neil O'Connor
Madison, WI
72 FIAT 124 Spider
12 Jeep Grand Cherokee Overland Summit
14 Ram 1500 Laramie Longhorn Eco-Diesel
ex-71 FIAT 124 Coupe
and a host of Audi's, Saabs, VW's, MOPAR's, Fords, and a Bimmer....
Yadkin wrote:It would take several multiples of my 170# weight to deform that seat back vertically, to the point of being a problem.
Its still is a well known weakness on the 124 Spider. The seat backs are not as sturdy as you may think they are and their weakness is a pain point that has troubled a great many folks.
In an accident you will get many times your body weight trying to deform the seat backs and rear end collision crash testing showed a tendency for the seats to fold back. The spec on the 124 Spider is only for a 150 lb driver and a 150 lb passenger so you are already over.
A forward or reverse impact would impact a horizontal load vector to the seat belt. The belt rides through the guide at the top of the seat frame with little friction, therefore any tension in the belt results in a force vector into the seat frame in the direction of the seat back, not a horizontal load.
The belt tension is a function of it's horizontal vector and the angle from horizontal. As that angle is reduced the vertical vector is reduced.
