I realize this is an ancient post, but I have done this recently and have answers to some of the questions. I hope that this may be helpful to somebody thinking about this swap.
I wrote about this on a different Mustang site, but this is the shortened/compiled version.
Short story, it is possible to put an Explorer 5.0/4R70W transmission in a ’66 Mustang in OBD2 trim without a distributor, without changing to a Mustang computer, and without modifying the hood. It is possible to get the PCM programmed to a non-emissions version and delete PATS. It is possible to use the Explorer front cover with a front sump pan/dipstick.
Long story. ’66 Mustang originally a 6-cyl/3-sp I swapped to V8 and AOD but never finished. Battery relocated to trunk. Shortened 8.8 Explorer 3.7 TracLok disk brake rear (14” Disc Brake steel wheels work fine, 14x6 Magnum 500 wheels required 1/8 shims both front and rear to clear calipers). Borgeson steering. Granada brakes. Shelby/Arning drop. I decided wanted an Explorer 5.0 with the GT40P heads and improved 4R70W transmission. It is arguably the pinnacle of SB Ford engine development. I bought a wrecked 2000 AWD 5.0 Mountaineer. I bought a 2wd transmission from the pick-a-part. I sent the PCM to “The EFI Guy” Garry in Colorado. He is the key to all of this. He turned off PATS, EGR, rear O2s, and all the fuel tank sensors. I pulled the PCM from the yard-driving truck and sent to him. He turned it quickly and I was able to put it back in the truck and drive it into the shop to pull the engine. Removed the main engine compartment wiring harness from the C115 engine connector. Since it was wrecked and the front end, the radiator and condenser were ruined-so I cut most of the nose off with a Sawzall. Disconnected the transmission from the transfer case (you really need a ½” half-moon wrench for this-OR-pull the access cover). Pulled the driveshafts and then transfer case. Cut the exhaust off (try to get the passenger side as high as possible so it clears the motor mount coming out). Disconnected the remaining lines to power steering and unbolted the motor mounts. Dropped the transmission crossmember and it was ready to come out. There is no good way to grab it. I ended up with straps around the exhaust manifolds. Glad it didn’t have to go high. After that it snakes out and there you go.
I used an early Mustang front sump oil pan and bought HiPo exhaust manifolds since these are the GT40P heads. Nobody makes an H-pipe that will fit either style manifold and clear an AOD or 4R70W (much less have O2 sensor bungs) so you will have to have at least a custom H-pipe. Put new spark plugs and wires on while it was out (glad I did, plugs will be no fun in the car). You can use earlier style lift loops on the exhaust manifolds (mine came from the ’88 Cougar) when you put it back. Pulled the AWD transmission and replaced it with the 2WD one with new front seal “while it was out”. I should have done the oil pan while the transmission was off, but I didn’t (or left this to do in the car by dropping the steering and support bar under the car. It’s pretty open with those 2 items removed). The 4R70W pan is by far the lowest point of the driveline. I should have swapped to an AODE pan and filter-highly recommended(EDIT-JUST GOT BACK FROM A RT66 TRIP-CONSIDER THIS A REQUIREMENT!!). Pulled the oil pan and figured out the oil dipstick. You have to keep the Explorer timing cover and unique accessories to stay distributor-less. Drilled a hole on the LH side of the timing cover and put a flexible dipstick in the only place it fits. There is not “meat” here on the right to drill for a dipstick like the ‘80’s style cover has. I had to get creative. I ended up JB Welding the bottom of the dipstick tube to the cover and had to cut notches into the p/s bracket for the tube to get to the top. I bought a generic flex dipstick, get the longest one you can so you can access it. After that, swapped the oil pump and pickup and installed the front sump pan. Also replaced the timing chain and water pump while it was apart. The FelPro 1-piece gasket with easy-ups worked well. So 2000 5.0 Explorer style oil pan and exhaust gaskets worked fine with the early pan and HiPo manifolds. Used stock 289 Motor mounts and AOD conversion transmission crossmember and mounts. Used an early Mustang 2 floor shifter and shift rod (that’s what I had), and the Explorer shift tab. Had to heat and bend the rod to make it fit. Took the ball off the Explorer shift tab and drilled it out to use the press in bushing. The transmission electrical connector cannot stay with the stock bracket, but it will go in on top without “dimpling” the floor or changing wire lengths. I have a Borgeson power steering box (no issue with HiPo manifolds and automatic) so the return line hooks right up. On the pressure line, I have an Isuzu Trooper line at the box spliced with a JIC fitting to the Explorer hose from the pump.
With the 4R70W, the Explorer flange is for a 1330 style U-joint while the Ranger, Late Mustangs, and Cougar use a 1310 U-joint. Originally, I used a 1310/1330 conversion joint (Spicer S5-134X) at the rear to balance it out with a driveshaft I had but it was too short. A 4R70W does have a 28 spline yoke like a C4, Toploader, or AOD BUT the OD of the yoke is bigger so you can’t use that style yoke without mods because it is loose in the tailhousing. That means without transmission changes, you have to use a 4R70W yoke which on the Ford side was not made with a 1310 u-joint, most seem to be 1330. A 4R70W 1310 yoke does exist in the aftermarket but is spendy. Another possibility is put an AOD tailhousing on the 4R70W. Just be aware of the yoke difference in your plans. So I bought a 2005 Crown Vic Police aluminum driveshaft which has the right 1330 flange on the rear and right yoke on the front, I had it cut down and balanced. Not sure a steel Crown Vic one would work. Aluminum one is same diameter over the whole length. Steel one is smaller at front and rear and big in the middle. Maybe/maybe not enough small to shorten? I ended up with 48.375” for a joint-to-joint on the driveshaft. I am not aware of anything Ford made in 1330 joint that is anywhere close to that length. Again, this was my car with that specific yoke.
On the electrical side, I am using the engine/ transmission harness from the Explorer with only 2 changes. 1-removed RH rear O2 sensor wiring to the transmission plug. 2-used LH rear O2 sensor wiring to get VSS up to the PCM. I am adding an old-school Ford VSS generator and keeping the cable speedometer. This only applies to the ’98 up transmissions if you want cruise (no VSS in transmission, in these VSS is generated in the rear axle and passes through the ABS module to get to the cruise control). Garry has YouTube videos on modifying these harness if you really want to streamline it. I elected to leave the C115 connector alone and take the mating front harness out of the Explorer and use it. It has a nice fuse/relay box that is way overkill for a Mustang. I am using it and an aftermarket harness for the Mustang to keep the electrical loads controlled. I did away with the Mustang starter relay on the fender and am using the Explorer system. The factory Service manuals for 2000 (and 1996 supplement) have nothing on the 5.0 so don’t bother with them. The 2000 Explorer/Mountaineer wiring diagram manual is good. I did a lot of wire tracing and thinking to get it where I can use the Explorer front harness mated to the aftermarket dash and rear harness. I left the front O2 connections in the stock locations. The RH side could be longer and access better, but it will work as-is.
Fuel system. I have a Tanks Inc. 22 gal 69-70 style fuel tank with Walbro pump. You don’t have a great place for a tank vent because the tank is the trunk floor. I kept Canister Purge and ran a vapor line into the engine compartment and used a 2000 Mustang vapor canister. It has a vent near the air filter. The ’99 up 5.0 is “returnless”. There is a regulator in the tank that returns fuel inside the tank. There is enough room on the pickup to add it (but maybe not on a 16 gal tank, I don’t know) but not enough room to physically get it through the opening in the top of the tank. So I am using a 2000 Corvette fuel filter that has a regulator built in it and a return line to tank. Or you could just have an external regulator and normal filter. One advantage of the Corvette filter is that it is 5 micron where the stock Explorer filter is 10 micron. I am running the fuel lines on the RH side and tucking the filter where the outer edge of the RH muffler would be. Fuel lines: I came out of the tank and over the axle with 3/8 pressure and 5/16 return (left over from an earlier incomplete 5.0 Cougar swap-as was the 5/16 Vapor line to canister). The filter is on the passenger side in the muffler dimple. Then it runs 3/8 to almost the transmission crossmember where it goes to 5/16 with a short section of plastic line and quick connects. Then through where the crossmember attaches and up the firewall to right under the heater hoses. Each line has a couple cushion clamps holding it. Then I used the stock Explorer 5/16 line/hose that originally went to the filter routed across the firewall and connected to the line coming from the new filter. I have a Mastercool flare tool and it is awesome for making fuel lines and brake lines. I highly recommend it for this type of custom work. The Mastercool tool also does a nice job pushing quick connects into the plastic line as well if you are careful and patient. I bought an Arvinode exhaust system so I don’t have to deal with an interference there since the chambered exhaust has no muffler. With stock fuel gauge you need a non-linear fuel level sending unit. I bought an ISSPRO RA9509-FORD-LP. They are made both linear and non-linear so be sure to specify. To use the sending unit that comes with the tank, you need a new linear gauge.
The PCM either goes nearby the engine or you can extend the harness and put it inside. I elected to not extend it. I bought a 2001 Ford Escape PCM box from the pick-a-part (note: rear is held in under the cowl, not from inside the car). I cut a hole in the firewall and mounted it. I patched up where the Cougar harness went in, the PCM box can’t go in the same place.
There is no room for the stock Explorer rear outlet a/c compressor in a 64-66 without major shock tower surgery. Again, you have to keep the Explorer accessories to stay distributorless. Everything else fits nicely in the Mustang engine bay. I got an oil filter adapter to use a FL1A filter. This Mountaineer had an a/c eliminator so I didn’t have to buy one and I used a routing with a shorter belt (Continental 4060832) that allows no eliminator anyway. A 2000 Crown Vic a/c compressor with top fittings might fit. If it does, it will require relocating the p/s reservoir. I think it will still be too close to the LH shock tower though.
The IAC valve is the tallest thing on the engine. I found CobraEngineering that offers an IAC mount where the EGR valve once was, but it is not exactly the right bolt spacing. If the IAC can’t be relocated, I think you will need a raised hood. Then I ended up removing the EGR elbow and mounting the throttle body directly to the intake plenum. This turns the throttle body 90 degrees. That has it’s own issues with throttle cables, but retains the stock IAC.
Using a ’69 Mustang BB (24”) aluminum radiator and a ’00 Cougar dual fan. I have a 61311378073--BMW temp switch (195/210F) in an upper radiator hose splice and Volvo relay for a 2-speed fan conversion. I wish the PCM would control the fans but it doesn’t. There is plenty of internet info on BWM switch, Volvo relay, and (originally 2-speed Taurus) fan.
The Explorer heater hoses work nice with the Mustang firewall holes. I used two of the Gates 18933 hoses. Bottom one used as-is. Top one shortened about 2”. Was told that Gates 21736 upper and 20702 lower radiator hoses worked on EFI conversions. 21736 does work on top but I was glad I had the fan sensor in an extension because without it the hose would be tight. The bottom is one of those domino-effect things. Because I originally kept the Explorer oil filter sticking forward (by the way, you can't rotate it, I tried), the lower hose had to account for it. Also the Explorer pump is 1 3/4" outlet. So long story short, a 20702 works at the pump end if put on backward and then I bought a 20608 hose for the 1 3/4" elbow to go at the radiator. Cut the 1 1/2" elbow off the 20702 and spliced them together.
Air intake. I have a universal 3 ¼” 45 degree silicone turbo elbow. Then 3” PVC sewer pipe with a 45 to a 3” rubber sewer connector to the MAF sensor and finally a generic cone air filter. I saw a later Mustang at the pick-a-part with a factory cone filter, but I had already done this. The air intake and coils on the Explorer 5.0 prevent you from using a normal MonteCarlo bar to keep the shock towers spread. I took a porta-power and spread them the 40” width of the bar. Then cut up the bar and welded an offset for the coilpacks and a place for the air intake to pass through. You can’t really move the coilpacks forward or low enough to clear a straight bar even if you wanted to.
I left the stock cam in it. It’s is plenty fast. It gets about 19mpg. With a better cam it would be even more impressive.
If anybody else does this swap, I hope this helps them not make some of the mistakes I made along the way.
Last edited by markdtn (5/04/2021 11:13 AM)
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ultrastang wrote:
Gets about 19mpg even with tiny tires and 3.7 rear. I wish I could have found a 3.55 rear to shorten, but they seem scarce. No cooling issues. I am quite happy with it. It is basically a 2000 Explorer with a Mustang body wrapped around it. It is plenty fast for me, but a cam and valve springs would probably make it even faster. For my purposes, it is exactly right. I can buy driveline parts at most any junkyard and parts house in the country but it is still a "classic looking" '66 Mustang.
