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Hybrid Clutch – Dave's Garage Zetec RWD Mk1 Escort Ep 9

Dave's Garage UK Zetec RWD Mk1 Escort – Episode 9 title card: making a hybrid clutch

With the adaptor plate made in Episode 8, the first-generation (NA) Mazda MX-5 gearbox will bolt to the ST170 Zetec. What it can’t do yet is drive anything, because no off-the-shelf clutch suits both the Ford flywheel and the Mazda input shaft. In the ninth video of the Zetec RWD playlist, Dave’s Garage UK mixes Ford and Mazda parts into a hybrid clutch. He admits he’s bought three or four clutch kits along the way and spent more than an RX-8 gearbox swap would have cost, but he hopes the lessons save someone else the bother.

Video: Dave's Garage on YouTube · watch “Ford Escort MK1 Restoration. MX5 Mk1 NA Gearbox to ST170 Zetec engine. Hybrid Clutch.” on YouTube

What happens in Episode 9

The parts that don’t work (1:30). He has two Mondeo flywheels. The 1.8 one takes a 220 mm clutch and the 2.0 one takes a 240 mm clutch. A Mazda 626 clutch disc fits the MX-5 gearbox’s splines nicely, and it goes on the 2.0 flywheel with the matching Ford pressure plate, but that flywheel and pressure plate are too big and fat to fit inside the MX-5 bellhousing. The original MX-5 disc is the opposite problem: it’s so narrow that it touches only a thin band of the flywheel’s friction face and would slip badly.

A 626 disc on the 1.8 flywheel (3:30). The 626 disc was sold as 220 mm but actually measures 225 mm, so taking about 2.5 mm off its outside edge would let it work with the 220 mm pressure plate on the 1.8 flywheel. A quick check shows that flywheel and pressure plate do turn freely inside the MX-5 bellhousing. The disc is too big to fit in his lathe, though.

Grinding it down (5:40). Instead he makes a simple mandrel. The disc’s splined centre is 22 mm, so a length of 22 mm pipe, bushed out to sit dead centre, holds the disc tightly. He spins it with a drill and takes a couple of millimetres off the edge with a grinder. He checked first that the disc contains no asbestos, and wore a dust mask anyway. The trimmed disc fits, and when the pressure plate is bolted up the diaphragm fingers pull in and clamp it properly.

A possibly better disc (7:23). Some searching suggests the 1.8 MX-5 clutch disc is 215 mm, so he’s ordered one. If it fits, he’ll use that rather than the modified 626 disc.

Bolting up and testing (10:11). The stainless bolts holding the clutch are only for the mock-up, and he plans to use 10.9-grade cap heads for the real thing. The gearbox goes on, one bellhousing hole is opened out from the other side so it clamps properly, and the clutch works. The release bearing sits correctly in the clutch and the fork lines up.

Does the bellhousing need centring?

A viewer asked whether the bellhousing should be clocked (measured so it sits exactly central to the crank). Dave’s view is that it matters less here. He says some gearboxes have input-shaft bearings that let the shaft move about, but this one has a bearing that takes the side load, and the gearbox shaft goes about 5 mm into the pilot bearing in the crank, which keeps it central. It needs to be close to central, not within a tight tolerance.

Still to sort

  • Starter motor. With the thick plate bolted up, the starter jams against a rib on the bellhousing. It didn’t show with the thin template because that flexed. It’s definitely a Ford-pattern starter, as the bellhousing came from an old Pinto-engined Sierra, so he plans to order a slimmer, more modern one.
  • Clutch disc. He’ll come back to it once the 1.8 MX-5 disc arrives.
  • Gear lever. He’ll shorten the shifter arrangement next time. Viewers told him it’s a common job on the RX-7, so moving the lever forward looks doable.

Lessons for your own Mk1

At the end he sums up the combination he’s heading towards:

  • Flywheel. Use the 1.8 Mondeo flywheel. The 2.0 one is too fat for this gearbox.
  • Pressure plate. Use a 1.8 Mondeo pressure plate, but make sure it’s the 220 mm one. He says 240 mm versions are also sold as suitable for the 1.8, and they won’t fit here.
  • Clutch disc. Use a 220 mm-class Mazda disc. He expects the early 1.8 MX-5 disc to be the answer.
  • Measure what arrives. His “220 mm” 626 disc was really 225 mm.

Mk1 context

This is the step that makes the conversion drivable. The Zetec was never meant to sit north-south behind a Mazda gearbox, so the clutch has to be pieced together from parts for both makes. Moving the gear lever forward, which comes up again here, is what will put it in a sensible place in the Mk1’s tunnel.

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