With the floor back in, the next job on Dave’s Garage UK’s Mk1 is room for a modern rear-drive gearbox. Episode 5 of the Zetec RWD playlist replaces the narrow stock tunnel with a wider automatic one – bought as a panel so a carpet set will fit – and shows the cut, offer-up and weld sequence.
Video: Dave's Garage on YouTube · watch “Ford Escort MK1 Restoration Project, fitting big gearbox tunnel” on YouTube
What happens in Episode 5
Why an auto tunnel (0:10). Dave built a custom tunnel for his Ford Popular and fitted an RX-8 gearbox in that, and he still has the jig. For the Escort he wants carpets, and no carpet kit exists for a one-off tunnel, so he buys a ready-made automatic gearbox tunnel for about £100 – about what a home-made one would cost, and the right size.
How much wider (1:41). Temporary bracing that held the shell while the floor was out comes out now the floor is secure. The auto tunnel is roughly two and a half to three inches wider than stock – a full hand span – which is what a taller modern box needs.
Offer up and mark (2:44). Both doors come off so the rotisserie jig stays balanced, then the temporary supports come away cleanly – the shell has barely moved. The tunnel drops in forward of the seat boxes. He marks around it with a Sharpie and cuts well inside the line.
Plasma cut (5:35). A budget Cut 50 plasma cutter, jerry-rigged with a pilot-arc gun, makes short work of the old tunnel and a chunk of bulkhead. He wears an FFP3 mask and notes he should use something better. After the first cut the panel sits tighter; a spare pedal box confirms clutch clearance.
Trim, spot-welds and flange (8:48). Tech screws hold the tunnel while he marks again. From underneath the extra width is obvious; he leaves about an inch of flange rather than cutting tight first time. A wire brush reveals the old tunnel’s forgotten spot welds into the floor pan, which get drilled out. Edges are tidied with a flat disc and dolly-formed to match.
Plug weld and seam (15:04). Holes are punched for plug welds and the tunnel goes back in on tech screws. One side gets a full seam weld for strength and to stop dirt collecting behind the flange; the other is plug-welded so it looks nearer to factory under the carpet. A gap on one corner is closed by bringing the metal in. After grinding there is room for an RX-8 or Mazda MX-5 NA box. He has since been told an RX-8 might not fit an auto tunnel; he thinks it will, and if not the angle grinder can enlarge it.
Parts, tools and materials mentioned
- Ready-made Mk1 automatic gearbox tunnel panel (~£100)
- Home-made tunnel jig from the Ford Popular build (kept, not used here)
- Plasma cutter (budget Cut 50 with a jerry-rigged pilot-arc gun) and FFP3 mask
- Angle grinder, flat disc, Sharpie, tech screws, plug-weld punch, dolly
- Pedal box offered up for clearance (a bias pedal box is planned later)
Lessons for your own Mk1
- Buy the tunnel that has a carpet kit. A custom tunnel is fine until you want factory-style carpets.
- Cut inside the mark first. An inch of flange is easier to dolly and weld than a hole that is already too big.
- Drill out the old spot welds. The stock tunnel is welded into the floor pan; forgetting them stops the new panel sitting down.
- Seam one side, plug the other. Full seam welds seal and strengthen; plug welds on the visible flange look nearer to factory once carpeted.
Mk1 context
A taller MX-5 or RX-8 gearbox will not clear a stock Mk1 tunnel. The automatic tunnel is the usual DIY fix when you also want a carpet set, and it is the route this build takes before the adaptor plate and mounts in later episodes.
Related
- Series page: the Dave’s Garage Zetec RWD conversion, episode by episode
- The previous video: Episode 4, the ST170 engine arrives
- Where the series starts: Episode 1, a DIY oil pickup pipe for the ST170 sump
- A different modern Ford twin-cam in a Mk1: Episode 5 of the Retropower Gordon Murray build, the Cosworth Duratec visit
- All our Mk1 Escort builds