• TR4A - Rebuilding the Seats Contd

    TR4A - Rebuilding the Seats - Part 2

    Those Tricky Foams


    I said this in the introduction but I'll repeat it here. Get fully moulded foams that are close to the original if at all possible.

    This will save a lot of work and quite possibly money. I reckon that it cost 40 GBP in glue and perhaps 30 GBP for extra foam and other upholstery materials, to bring the reproduction foams I bought, up to the proper size.

    To be fair, the foams for the seat-bases did not really want much attention. They came made from two pieces of the stiff, white coloured, kind of upholstery foam and were cut close to the size and shape of the moulded Vitafoam originals. They were just a bit to “flat” being made from ordinary sheet.

    Originally the Vitafoam was covered with an extra layer of thin foam and I did this also. I used 3/8in thickness and glued it around the inner-face of the “horse-shoe”. The extra layer of foam helps to make a “pocket” to bond the cover into. But it was still too flat.

    Attachment 28314

    You can easily alter the shape of foam using rough trimming with a scalpel or electric carving-knife. You finish smooth with an angle-grinder with an ordinary steel grinding-disc, yes really!

    I used another method because I did not want to reduce the thickness of the foam, it being already barely as thick as the original, which had seen many years of being squashed.

    I cut a horse-shoe shape from 1/2in upholstery wadding, making this a little smaller than the raised area of the seat-foam. This “softens” the flatness and makes a good profile on the finished job. It was tucked in underneath the layer of 3/8in foam of foam.

    Attachment 28312

    No wadding, a bit too flat for my taste.

    Attachment 28299

    Wadding adds the curvature required and is cheap and obliging stuff to work with.

    Attachment 28300

    If only the foams for the seat back were as simple. These were originally moulded in yellow foam, styrene I would think. This ages somewhat better than the grey Vitafoam and were almost reusable.

    The replacements were made a bit like the base-foam, but from a softer grade of dark grey upholstery foam. Its really important that softer grade is used, or you will need some fancy tackle to get the top-covers to pull down.

    They were actually a three part sandwich, there being a triangular wedge piece running down both vertical sides. The cross-section of this wedge was the same for the whole run. But the moulded original is much thicker at the bottom than the top. It was wedge shaped in two directions.

    I have borrowed the following two images from a post on the BritishCarForum site and they show the exact same kind of foams that I started with. So these must be a commonly available items.

    Attachment 28301

    Attachment 28302

    The end result is actually pretty good. But this is Vinyl not leather and it's a bit more forgiving.

    My guess is that wedges tapering in two directions are too tricky for the ordinary foam-cutting machines to do.

    I bought an additional wedge piece and cut it transversely with a scalpel, so as to make two wedges that tapered in the same way as the moulded original. One bought-in wedge served for both sides of one seat.

    The new foams were split on the glue line and I spliced in the additional wedge pieces. I used the white grade because of its greater resilience. I intended to increase the stffness if the side pieces. I don't really know why, except my daily-driver seems to be like this.

    Attachment 28303

    I added a tapered layer of the kind of thin foam with a fabric layer, called “scrim” I think. This supports tension. I glued it so as to set the edge to make the side-profile a match to the shape of the original foam. Quite tricky this, you need three hands.

    The foam seems to lean “the wrong way” but it won't do this when the cover pulls it. The white wedges are about 1in thick at this point.

    Note how the 3/8in foam layer is floating free on one edge. It stays this way. It you glue both edges then the tension of the cover would cause it to “balloon up”. This way its pulled into place by the cover and lays in place behind the stitched seam.

    The back-foam was about 2 in “taller” than the back of the frame. I very nearly cut this off. DONT! This extra foam generates a lot of tension as you pull the cover down but this is vital to get the right profile in the top rolled edge of the seat-back.

    The original seat had a loop of foam that followed the outside of the seat-foam. One piece all the way around. I did this too using 1/2in thick grey foam.

    This proved tricky to keep in place when fitting the covers so I glued it, but only in a strip about 3/8in wide, around the pointed edge of the main foam. This is another example of leaving it un-glued over most its area, so the cover brings it into place as it compresses the foam.


    Attachment 28304

    You can choose to use brush-on high-temperature impact-adhesive or the quick and easy spray-can stuff. Do not expect the can to generate anything like the joint strength of the brush-on kind.

    Mostly so far, you have seen joints that I made with the strong stuff. But bear in mind that this makes quite a hard layer when it is fully set. I can feel this in places, through the cover. So with hindsight a bit more use of the spray-stuff in non-stressed joints would have been good.

    The long tapering wedges for example would stay in place without a really strong adhesive. After I glued these with the strong-stuff I found that that this had made the joint stiffer than I really wanted.

    Maybe you are having trouble visualising the shape of the wedges that I “let in” to the sides. I should have taken a photograph but missed the opportunity. The next picture will help though.

    Attachment 28305


    Bonding the Covers into the Foam

    If you search for pictures or videos of seat-covers being fitted, you will see the usual arrangements, where the cover has wires or sewn-in tabs. These get pulled into place by a wire-loop called a “hog-ring”, they pass through the foam and attach to a metal part of the frame.

    The 4A seats aren't anything like that. The centre-panels of the covers are sewn into the outer “horseshoe-shaped” piece and this leaves a thick seam about 1/2in wide.

    This seam is then glued into the foam. Study the old foam to see how the factory did this.

    Attachment 28306

    I prepared the new foam to accept the seam, by making a cut into it, about 1/4in deep. The cut went at an angle of about 5-10° below the glue layer, rather than following it or going straight down into the base layer. I had also added a layer of foam and this also helped to form a pocket to bond into. The leather seams are stiffer than Vinyl and this angle conforms with their “natural” lay.

    The method was more or less the same for the seat-bases and the seat-backs.

    The foam left over from making the “horse-shoe pieces”, went under the central fluted panels. It must be trimmed back a bit, so as to lay flat inside the bonded area, of course.

    If you compare the finish of these centre-panels on my seats, with the black Vinyl one above, you can see that mine are more “perky”. This is a matter of taste and you could let them stay flat if you wish. But you probably have to put this in before you do the bonding, so make your mind up!

    I prepared the seam by gluing the layers together with the strong impact adhesive brushed into the gaps. The aim here was to make sure I got both layers bonded into the pocket.

    A trial fit or two, without glue, showed the technique needed to push the seam into the pocket. I found it would stay there with no glue. A few marks were made on the foam and the cover to show the correct position.

    I could not imagine myself getting the seam into the pocket, in exactly the right place ,if obstructed by impact adhesive which “catches” as soon as it touches.

    I have a lot of experience using Polyurethane-Sealant, my favourite brand is called Tiger-Seal. This is very sticky but takes about half an hour to cure. It does not grab on first meeting.

    White-coloured sealant was squeezed into the pocket using quite a big hole in the end of the nozzle. It took three passes, four in some places, to fill the pocket. After each pass I closed up the pocket and pinched it together to drive the sealant into the pores of the foam.

    Judging the quantity, so that a little will exude when you insert the seam, is pretty tricky guess-work. Maybe it will help to know that I consumed almost a whole tube to do each seat. The base and the back both took about half the tube.

    To keep the cover in place while the sealant cured, I cut a piece of cardboard to protect the leather and got four house-bricks handy.

    It was simple to push the cover-seam into the sealant. It slid in easily and I could move it to line up my marks. As I piled on the bricks I was careful to ensure that the corners stayed put. Similarly the ends where the seam left the pocket.

    At this stage I had no idea if this would stick or simply pull out once it had set. This seam bonding comes under a lot of tension, particularly at the top of the seat-back.

    Its impossible to do all this and photograph doing it at the same time if you are working alone, so you will have to make do with a shot of the end-section, taken after the sealant had cured.

    Attachment 28307

    Note the bevel, cut with scissors, on the edge of the foam in the centre-panel. The white sealant is easily visible below the cover, but there is actually also some just visible on the top side.

    Now for the Wadding

    There was no wadding in the original seats. But when I pulled the covers over the foam for the first time, it was obvious that these seats were designed for Vinyl and not leather. No amount of pulling, this way or that way, would remove all the ripples and puckers.

    The corners of the horseshoe shaped outer where they meet the centre-panel, were a particular problem. There just isn't enough “push” being generated by the foam to smooth out the leather.

    Much the same happens on the outside faces. The seat-bases as usual were less of a problem than the seat-backs.

    In case you don't know, wadding is a kind of open jumble of springy white Viscose fibres. I used 3/4in thick, but with hindsight 1in thick would be better. You can “rearrange” it locally to get more or less thickness or tear off bits and stuff them into gaps. Its obliging stuff really. And quite cheap.

    I covered the whole surface of the back-foam with wadding and loosely fixed it with the spray can upholstery glue, but only on the outer edge, as explained before.

    On the base-foam I just used wadding under the normal-foam sheet to get a more rounded look, as previously shown.

    Attachment 28313

    This fixed most of the problems but the corners were still not to my satisfaction.

    The support structure in these tight corners needs to be almost rigid to get the leather to look smooth. Rigid and exactly the right shape or you get a kind of bubble.

    Attachment 28308

    I never give up on a thing like this. There is always a way out.

    Attachment 28309

    and the result is!

    Attachment 28310

    The two pads were made from offcuts of the hardest white foam, bought to make the head-rests.

    They were roughly shaped using scissors and scalpel and finished with the grinder.

    Its not obvious above but you must bring them to a “feather-edge”. The dome shape must be proud when the cover is off, but not by much. Needs trial and error. Mind your fingers!

    These were slipped in above the main foam and under the layer of wadding and secured with only a little glue from the spray can. The whole thing reminded me of a certain cosmetic surgery procedure, often to be seen on the TV.

    Building onto the Frames

    So now we come to the operations needed to secure the foams in place and get the final fit on the covers. Start with the bases because these are so much simpler to get right.

    The first job of course is to install new diaphragms. You pull the hooks into place with string. Dont fit the two rear-hooks until later and make sure they don't fall out and get lost!

    You can see that I have filled the gap between the two re-inforcing plates with white foam.
    Its actually closed-cell polyethythene foam recovered from packaging.

    I prepared the base-foams following the method found on the original factory foam. This is Hessian glued on the back of the foam and folded over onto the frame. This gives fore-aft restraint on the base-foam.

    By this stage I had made quite a few trial-fits with the foam in place on the frame. While doing this I kept the cover in place with a selection of clips and pegs.

    You cannot gauge if you have the right amount of wadding and foam until you actually get the cover restrained in more or less the final position. The foams alone are too floppy to do this.

    Getting the cover over the edge of foam is quite easy. You just kind of roll it and eventually it will jump from being inside-out on the top of the foam to being the rightway-out and enclosing the foam.

    The trouble is then there won't be any room for the frame and no free material to fold over the frame. The whole cover will be full of foam. I knew this would happen of course, and had already put together the means to force the frame into the foam.

    Here its about half-way into the final position. At this point check that the foam is correctly positioned both fore-and-aft and side-to-side, glue the Hessian flap to the front of the frame and clip the other flap around the rear cross-bar.

    Loosely fix a layer of the thin foam, with the spray-can glue, to give a padded feel to the skirt.

    The frame can now be squashed down to its final position and the leather-cover drawn over the skirt and clipped temporarily in place.

    You need to decide if you want the leather seam to sit on the top surface or on the skirt side of the corner. Whichever side you choose will have a slightly “lumpy” line by the piping bead.

    I chose to have the seam on the top. Feel down inside the gap between the foam and cover and set the seam as you want it.

    Make sure the cover sits in the right place and you are happy with the look of it.

    You may notice two long screws poking up where the rubber feet normally go. This is so I can set the seat down the right way up without spoiling the paint on the frame rail.

    I used Hessian on the top edge of the back-foam also, even though the factory did not. This is because, as mentioned earlier, the new foams were much “taller” than the original moulded foam. About 2 in actually, which is a lot and I needed some help to get them into the right place.

    I added a loop of self-adhesive foam tape, 1/4in thick, to the frame and this can just be seen above. It runs under the Hessian and right down both sides.

    It may look as if I have omitted wadding on the top of these.

    The cover will be pulled so tight in this area that the grey foam will be collapsed virtually right up to the frame. This will get the piping to match the profile on the original cover.

    Because the seam in the top of the back-cover takes so much tension and because I wanted to make it “point backwards”, which it tries not to do, I decided to glue it.

    Glueing seams like this makes them a bit more obvious because the cover then shows a line at the edge of the seam. Its not normally the done thing. I didn't go right the way down the sides.

    I recut the slits in the cover around the corners, widening them to a true V-shape before gluing them down. These corners want to bunch up because there is really too much material once its folded over the frame. Anybody who has ever covered anything will know this effect.

    Quite a bit of trimming and fiddling was needed to get this part to sit smoothly on the corners.

    A bit of extra wadding was stuffed in here to get the right finish. Remember that these seats are not symmetrical in this area, so what works on one side does not necessarily work on the other.

    Pulling the back-covers over the foam is easier than the base. No extreme clamping is needed.
    Just squeezing by hand and temporary clipping in place. Gradually the correct profile for the piping can be achieved by comparing with the old cover.

    Now you have the strenuous task of installing the long spring that holds the bottom of the back- cover. This threads through the tube sewn into the cover and hooks into the lowest holes in the frame.

    These are tough to fit on an original frame. But I have added reinforcements in this area and they don't make it any easier!

    String alone would not quite get these into the right position to engage with the frame. They needed a tweak, from narrow-jawed Mole-grips, as well as stretching with string.

    Those screws sticking up were found to have a second use. The string was looped around the frame and secured on the screw. This kept the spring stretched and allowed final positioning with the grips.

    I did this job on my dining-room carpet while my wife was out at work. This meant I could give them a good wrestling match, without scuffing up the paint or the leather.

    The long leather flap then passes around the “cross-bar” but the finished side goes against the bar.
    Careful where you put the U-clips because the diaphragms and the clips that hold the real panel all argue for space on this bar.

    Finishing Off

    Once you are happy with the fit of the covers secure them to the rails with the U-clips. I used a mixture of old and new ones. If you push these on and then change your mind you can get them off without wrecking the leather covers, almost! So try to get them right first time.

    The small rubber feet were added so that I could put the seat down after the big rubber feet were fitted in place of the long screws. The big feet dont touch the ground!

    This picture also gives an idea of how tricky it was to engage the hook of the spring into the frame.

    The small rubber feet also provide a means of securing the “flap” on the rear-panel to the curved part of the frame. Its also held by the big feet and some U-clips.

    The two big washers bolted to the two front mounting-points are there to save scuffing the paint. They are only just big enough to be any good for this purpose.

    Note the use of a small screw and washer to trap the end of the top-cover. Originally this was done with a ring-clip around the frame-tube. The reinforcing plate are in the way for this to work and the leather is a bit too thick for them to hold properly.

    There are a lot of useful images missing from this. These are included in the full version, 3.5MB in pdf format, available by sending me a Private Message on the BCF Forum.

    Alan J Turner

    England

    July 2013
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