TTAC Project Car: The Deeper You Go... (Part II)

Do enough tasks independently from each other and there’s enough content for a two-fer update on TTAC’s Ford Sierra.

So let’s get to it.

We ended our last installment with the completed install (ish) of the T-5 transmission, at least from the bottom. The top was far easier: upon removal of the (extremely simple and logically designed) console, the MGW shifter dropped into place with almost no issue.

Zoom in and you can see a shiny spot at the front of the aperture: just a bit of grinding to clear the stop bolts if/when I get a little too proud of the Sierra’s future accelerative capacity from 2nd to 3rd gear. The bolt at the rear (for the 1-2 shift) has no such issue, clearly.

Notice two dime-sized holes near the carpet. Those allow easy installation of the shifter at the front — and removal without resorting to dropping the gearbox!

The four threaded holes are original to the automatic shifter, and mercifully those are the same holes to bolt down the donor Merkur XR4ti’s heat/NVH shield for a factory look.

The T-5’s leather knob with vintage Ford “turbo” lettering was installed to ensure my random eBay purchase worked without needing different threads. But the eyes deceive you!

Because this isn’t a leather-wrapped shift knob from a Thunderbird Turbo Coupe, Mercury Cougar XR-7, or Mustang SVO. It’s a resin reproduction made by a brilliant enthusiast for the Turbo Ford community — every stitch and grained leather bend comes correct. The only downside is when you grab the damn thing and realize that luxury isn’t even skin deep. Totally worth the durability, right?

Combined with a spare leather boot from a long-forgotten TTAC project car, this is another finishing touch for such a bizarre project.

Rounding out the Sierra’s drivetrain means differential discussions. The 1983 Sierra’s entire rear subframe joined the front in a scrap pile, while the Merkur’s assembly bolted right up. Why? The perks included a rear sway bar, stiffer springs paired to high performance (aftermarket) shocks, and the same 7.5-inch differential found in the Cosworth Sierra.

While the internet is full of 7.5-inch Ford haters, there’s no need to upgrade to the legendary Ford 8.8-inch differential in the Sierra. Well, there’s no need for an 8.8-incher in a 5.0 Fox Mustang either, unless you love doing neutral drops or have enough power to run high 11s in the quarter mile. But I digress…

The European Ford 7.5-inch differential is completely different than what you’ll see in a USA Ford product, even that independent rear in a V6-powered 1989-97 Thunderbird — which makes things tricky.

Thank goodness this crap is already sorted out, then memorialized on the Internet! And you can PayPal a tidy sum to MC2 Racing for the following:

1. Buy MC2’s custom made Differential Carrier Bearing Tool. (above)
2. Use it to disassemble your Merkur rear end, and ship the side axle adjusters to MC2.
3. Buy MC2’s rebuilding service for the side axle adjusters.
4. Have MC2 ship those back, along with an Eaton LSD and a rebuild kit.

Not cheap, but it installs pretty easily. Well, I didn’t do a damn thing; the guy crazy enough to take on this project (Brian) did it with his years of differential experience.

With the differential on the bench, let’s wheel the Merkur (sitting on furniture dollies, in the background) back on the lift to take the remaining items from the rear: fuel lines, fuel tank, brake lines (in case they are bigger and not rusty) and anything else we see that might help us out.

I was assuming the EFI system, freshly dropped from the body, would be a huge labor and cost savings for the Sierra’s resto-modification.

No dice.

Turns out the (surface) rusted Sierra’s back end is a bespoke bit: the floor pan is different than a Merkur. While the aforementioned T-5 transmission installation was a headache, the larger spare tire well (for a full size spare) made an absolute mess of my plan to install the Merkur’s external fuel pump.

Even worse, the Sierra’s gas tank neatly fills the space next to the full size spare. Not so with the Merkur: this photo of a Mustang tank is similar to the Merkur, showing how it installs below and to the side of the spare tire well.

What’s the plan now? Remove the Sierra’s tank and do not trash it. Either it will be modified to accept modern aftermarket fuel pumps/pickups or it will be a guinea pig for fitment before sourcing a new one from the UK.

Dropping the tank netted somewhat good news: the inside was relatively clean and the factory sending unit is ready to go back to work giving information to the fuel gauge. The sending unit’s tubes that feed the (formerly carbureted) engine will be sealed shut, of course.

With dreams of installed EFI plumbing dashed, the subframe-less Merkur gets lowered onto a forklift to leave the shop, permanently. Much like the Thunderbird Turbo Coupe in a previous installment of this series.

It was both entertaining and depressing to see a rust-free Merkur, a once premium Gran Touring offering, reduced to clinging to the tow straps holding it to a forklift.

That said, the Merkur shall live next to its German brother for a long while, as we still need the (unique to 1989) master cylinder for the best performance with my brake upgrade. And who knows what else!

Oh, about those brakes.

We’ve already upgraded the Sierra’s front brakes to the larger Merkur discs, but the rear drums have an easy-ish upgrade: the setup used in the 87-88 Thunderbird Turbo Coupe and the ’93 Mustang Cobra!

Just remove the rear drums (harder than I expected because of the independent suspension) and bolt this funny-looking adapter, sourced from a member of a Merkur Facebook Group.

With dirt cheap (like $10 each) rotors from Rock Auto installed, the (almost) finished product now means the Sierra can roll on four-wheel disc brakes, even if they can’t stop themselves!

And, just like the T-5 crossmember from our last update, Brian gave the calipers a fresh coat of brown paint to complement the Sierra’s Rio Brown coachwork.

What happened to progress on the engine?

After many hours reading Merkur shop manuals and wiring diagrams, the hard reality set in: the EFI harnesses from my left-hand drive donor cars (Thunderbirds and the Merkur) will never work on a right-hand drive Sierra.

Turns out you can’t just cut/loosen the wiring’s loom, flip the harness upside down and route the engine wiring to the “wrong” side of the dashboard and extend a few wires. Every wire needs lengthening, from the computer’s intended location inside the dash to the air meter’s connection on the front and opposite side of the Sierra.

But there’s a light at the end of this tunnel.

A wonderful person named Ron Francis makes bespoke wiring harnesses for many engines, and he has two offerings for the Ford Lima 2.3 Turbo: this one has a junction box thing called a Telorvek, ideal when doing all this to a Right-Hand Drive vehicle. Why?

1. The Telorvek (hopefully) hides behind the Sierra’s battery, shooting long, cut-to-fit wires back to the engine bay and 3 feet of harness into the dash for the computer.
2. I can now use the smartest computer of the bunch (LA3, the first in the picture) without having to rewire a Merkur engine harness.
3. The new computer uses an Air Charge Temperature (ACT) Sensor, and I already had the ACT’s hole in my ported upper intake.
4. The Telorvek has provisions for electric fan wiring, too!

And while I wait the six-ish weeks for the harness’ creation, it’s pretty clear that I have my work cut out for me. My vacation time shall never be put to its intended use!

More to come when TTAC’s Sierra clears the next hurdle.

[Images: Sajeev Mehta/TTAC]