This will followup, after my "Seat Back Repair" thread on this forum,...
Upholstery tear-down, foam bun repair, and application of new upholstery (including some innovation) is covered. Upholstery source links are re-posted in a post near the end of the thread, including upholstery vinyl by the yard to match,...

Upholstery Tear-down:
The Fiat Spider is upholstered in the same manner as most cars and is a simple study. The design reduces the number of hogs rings necessary for installation,...
The Fiat seatframe is removed from the car in one piece by simply moving the seat toward the rear, to it's track limit, and removing two 4mm Allen bolts that attach the track to the floor bracket. Then move the seat as far forward as the track allows, and fold the upper seat forward. Remove the two rear track bolts. Get a good position and grip, and lift the entire seat out the door.
My seat hinges have snap on covers and the hinges remove with a phillips and a 13mm for the hinge bolts.

Seat Bottom:
This is usually the number one item necessary in most vehicles because it wears out faster than the rest of the upholstery.
A stiff vinyl strip runs around the bottom of the upholstery vinyl and slips into a track at the bottom of the seatframe. It is easy to 'roll' this strip out of the track,...push the cushion of the seat down to ease the tension, and start at the rear:

On either side of the rear of the frame, just under the hinge mounts, you'll find a pair of 'hidden' hog rings that will need to be cut:

they attach the upholstery to bottom of the foam bun at the rear.
Next you 'roll' the stiff vinyl strip out of the track (push down on the cushion to ease the tension) around the circumference of the seat bottom and turn the upholstery inside-out:

Now you are ready to find the hog rings that attach the three upholstery wires to the foam bun wires.
There is a wire that runs down each side of the upholstery and one that runs across, nearer the front. Easy to see the arrangement, at this point.
Strong fingers to expose the hog rings! Search along the attached edge of the upholstery and you'll find them. Cut four on each side and two on the cross-wire. Here's a pic of the upholstery removed and inside-out with the wires in place (sorry, my forward one had busted loose!):

Save the wires, if possible! And use the old upholstery to guide hog ring placement during re-upholstery.
I need to repair/replace this bun, so I used a putty knife to scrape the bun away from the frame. It is contact cemented along the sides, and along an area to the front and rear. Mine scraped away cleanly, without damaging the bun. Here's a pic of the cemented spots:

Re-assembly is the exact reverse of this, with application of contact cement and hog rings as per the factory. Turn new upholstery inside-out, install wires, hog ring wires to bun wires (there are "depressions" in the bottom of the foam to push up on the bun wires, to align them with the upholstery wires during assembly).
WARM the upholstery (best done in the sun), and roll it over the edge of the foam bottom, while slipping the stiff vinyl strip into the track (pushing down on the foam to ease the tension). Hog rings at the rear and the rear vinyl strip. Reassemble and reinstall seat.
Had to address upper seat frame repair on the driver's side, so I did not get pics of it's disassembly, but I'll get pics when I do the passenger's seat. It is upholstered in exactly the same way, but finished a little bit differently,...
More very soon.
I sure hope this helps some folks tackle re-upholstery!

On the “wires” (known as “lists”). I’ve found cutting up a wire coat hanger (the white coating over metal type) and bending the ends over to match the originals creates a nice rust-proof item that installs easily.

toplessexpat wrote:On the “wires” (known as “lists”). I’ve found cutting up a wire coat hanger (the white coating over metal type) and bending the ends over to match the originals creates a nice rust-proof item that installs easily.

For less than $20 you could also get around 25 feet of stainless steel wire that will work exceptionally well for replacing the lists too.

wetminkey wrote: The Fiat seatframe is removed from the car in one piece by simply moving the seat toward the rear, to it's track limit, and removing two 4mm Allen bolts that attach the track to the floor bracket. Then move the seat as far forward as the track allows, and fold the upper seat forward. Remove the two rear track bolts.

They aren't Allen bolts unless they've been replaced. Stock are Philips head.

I have no reason to replace the "lists". I do not replace what can be reused. I don't know why that topic came up,...
My 3/79 car has Allen cap bolts,...replaced bolts are metric hex on my seats.

both my early 79's made in july 78 have Philips head screws metric i assume.

but who cares....

cheers
dinghyguy

I've got phillips that hold the seatframe to the slider-track, but Allen cap bolts that hold the slider-track to the floor bracket. You have to remove the 4mm Allen cap bolts to remove the seat from the car.
You'll not get to those phillips, without removing the seat first!
Sorry, I mis-spoke about any replacements. Only replacements in my car is one of the driver's seatframe to slider track bolts, and it's an Allen relieved-cap bolt.
And who cares, anyway? The point is,...remove the seat, HOWEVER it is attached.

wetminkey wrote:I have no reason to replace the "lists". I do not replace what can be reused. I don't know why that topic came up,...
My 3/79 car has Allen cap bolts,...replaced bolts are metric hex on my seats.

The old lists can be more prone to snapping off where they were originally bent especially if there is any wear or corrosion at the point they contacted the seat frame as corrosion of any kind will cause them to become even more prone to embrittlement when they are unbent for removal and then refitted with a new bend in them. Considering the cost and effort involved your usually better off replacing them with new especially on those that thread through pockets in the upholstery.

interesting......on both mine the bolts that hold the track to the floor are Philips screw heads. Slide seat each way and undo all 4. I have never even looked to see what holds the track to the pan......based on what you say i expect they might be allen head. IE your car is backwards to both mine, or perhaps in Canada we do it the other way round from the US!

dinghyguy

Do we really expect a 40 year old car to have all the original fasteners especially on a high wear item like seats which could be on their second, third. etc set of covers/upholstery?

My car has it's factory installed upholstery still on these seats, guys,...
I doubt that the seats have EVER been removed from the car by a PO,...and both seat fasteners are identical, and in the places that I describe.
The single fastener replacement was by me,...when I did my "mouseproofing" (see "The Party's Over" in Fiat Related), years ago.

Perhaps yet another example of Fiat non-standardization……
Back at the ranch.....how goes the foam wrestling? pix?
What are you planning for the seatbelt holder bits on the top of the seats?
dinghyguy

Had a sudden family emergency, so I've lost the last week +,...
I bought some stuff that I can mix to create low-density foam, but I haven't experimented with it yet,...not sure how to contain the liquid components while curing,...
I'm going to purchase some thin foam and try the contact-cement, hot-knife carving method if I cannot figure out how to do this.
Anyway, working on it,...Good thing I haven't got it done, because the cost of the emergency that I spoke of is going to put upholstery off until Jan/Feb.
I'll still have lots more pics coming,...of dis-assembly of the seat upper (I'll show off some INTACT 40 year old, burgundy, factory upholstery!) and the rear seat. I'll also throw in a post about re-covering the rear side panels,...
I've determined that these guys have nice swatches and their dark red sierra vinyl seems to match my factory upholstery's non-discolored spots,...
https://www.carupholsteryguys.com/categ ... w?cat=2038
They also charge nearly half the price of the other sites that I know of,...autoberry.com and worldupholstery.com. And the swatches that I received from those sites were of the same quality and thickness. In fact, perhaps with a thinner color layer in the vinyl in one case,...
I think that's all I have for right now, I'll get on the foam repair and more pics ASAP.
Todd.

Goodness,...this looks interesting!
Didn't know you could that with dense foam and a electric carving knife,...
https://www.youtube.com/watch?v=32bMlq-9JUc
(right click, and open in a new tab,...)

Due to the video, I did some research and found this product:
https://www.sailrite.com/NG633-Foam-Loc ... esive-12oz
I also find a selection of upholstery foam available online, and my wife has gifted me her electric carving knife,...!
I'll play with my chemicals and make some foam,...and order some upholstery foam to experiment with.