Wednesday 11 September 2013

E21 316: Fitting E30 rear sport-seats - or having a go anyway.

Stock fit works, but leaves big gaps.
As with the front seats I used HSVTurbos build [here] as a rough guide. His rear bench-seat is the all-sponge kind, whereas mine have the sponge base, but a sprung back-rest, possibly due to the folding arm-rest or model year difference. This means I have a metal frame to work with on the back-rest, so it can be pressed flat to greatly reduce the proud fit at either corner, but also means more needs to be cut away than just blobs of sponge. The E30 coupe's rear seat-pan, the body-tub and front doors are almost identical dimensions to the E21, so the rear seat-base just slots in. There are no brackets along the bottom-edge to clamp the squab down, but with it seated flat and wedged under the back-rest these may not be necessary, although fabbing some up might be worthwhile to stop the carpet sagging down in the footwells.

The general shape of the back-rest is more or less the same as the E21 and the hooks fit into the existing brackets, though the E30's parcel-shelf is curvier, causing the back-rest to stick out slightly at the top corners. The back-rest also sits slightly higher, leaving an inch gap at the bottom between it and the squab. If these gaps don't bother you then the seat works fine like this and will only need a little chopping off each upper corner to achieve a pretty good looking fit. If they do, then a little more work is required to seat the back-rest flush and minimise the corner gaps.

The main problem here are the seat-belt reels, which protrude from the bulkhead and fill up where the upper corners of the back-rest want to be. The back-rest bolsters are also slightly too broad, though the centre of the rear frame is more or less a perfect fit to the E21 bulkhead.

Modifying the Back-rest:

1. Bend up the small hooks holding the cover material in place over each side edge of the back-rest and pull the fabric clear of the metal frame.

2. Cut away the side-support on each side of the frame, leaving just the edge of the 'mattress' frame that holds the springs, as in the photo below. The brackets at each bottom corner should come away here too.

3. Cut in half the metal bar that runs between the centre and bolsters, the one attached to the top spring in each corner, and trim away the top spring as close to the frame as possible.

4. Cut the metal bar running along the top of the frame about 4" in from either top corner

5. Cut away the boar-hair matting along each side of the back-rest to reduce its depth by about half.

6. Cut a 2" square from each top corner of the boar-hair matting to give a recess where the seat-belt can run freely back into its reel.

7. Replace the fabric cover, hooking it to points on the mattress-frame and tucking it under the springs. At each top corner, I pierced a hole and ran a cable-tie through to hold the folded fabric clear of the seat-belt reel.

Fitting to the E21:

To get the back-rest sitting flush to the seat-base the original mounting-brackets may have to be abandoned in favour of slotting the hooks on the bulkhead directly into the top of the back-rest frame. The original lower brackets are attached to the frame here and may need cutting off for a tight fit.

1. Hook the top lip of the back-rest frame over the metal hooks on the bulkhead. Press hard to make sure the metal bar gets over the hooks and not just the boar-hair and fabric. Give each side a good knock down onto the hooks. The top of the back-rest should be about 5mm lower than the parcel shelf.

2. Fit the centre arm-rest and lock the clips into place. The back-rest should sit a bit proud of the bulkhead and need pushing flat. Drill two holes through the back plate of the arm-rest and bulkhead. Fasten it together with two bolts or pop-rivets. Not only will this hold the seat in place, it will also stop it moving when the arm-rest is lowered.

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