COMPLETE foxbody 4r70w swap

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COMPLETE foxbody 4r70w swap

Unread postby SlowBox » Wed Aug 08, 2018 10:05 am

I've been working this for several weeks now planning and researching and buying and I've come to find that there is not an all-inclusive fox 4r70w write-up anywhere on the internet. My goal with this thread is to change that.

After having a fox with a stalled 3 speed auto once before, I never want to own another street-driven car without OD again. With 3.55s and 26" tall Mickeys, the car still tached 3k rpm at 60mph with an unlocked converter in a C4. Too high to take out on the highway. After the turbo went on my current DD fox, it wasted the T5 and in short order. I knew from random threads and social media posts that a late model 4r70w was going to be the cheapest option to hold the power and keep the car comfortable. I can't afford an Astro gearset or TKO or T56 so keeping the car original is out for now.

Picking up the transmission was the easy part. I paid $140 for mine with a stock V6 Mustang converter, but missing the shifter and cable, dipstick, and external transmission harness. Still a good deal. The 3.8 (Mustang) and 4.2 (F-150) 4Rs share the same bellhousing bolt pattern as the Windsor blocks, but 2002 was the last year they came with a worm gear cut into the output shaft to run the VSS and speedo. MOD MOTOR 4R70WS WILL NOT FIT YOUR SMALL BLOCK. Anyway, look for a yellow cap where you'd expect to see the speedo drive, snatch it off, and shine your flashlight in there. They're hard to miss.

**Be warned that the truck transmission is an inch longer than the Mustang one, not that it's a huge issue if you're already getting a driveshaft cut and crossmember made. Readers also need to understand that while the 4r shares output shaft spline count and size with the AOD and T5, the yoke is ~.100" larger in diameter which will require either a 4r70w specific yoke on your driveshaft, or the tailshaft housing changed out for an AOD piece. Neither of these scenarios is a big deal, but it will piss you right off when you're trying to finish the car.**

In 1997 the 4r70w underwent the last real update that swap guys need to worry about. The valvebody wiring harness became a printed, clip on piece of plastic. This adds a touch of complexity to swapping TCC noids since this solenoid also went from 1 ohm to 10 ohm in 96 with the transition to OBD-II. A 1996+ NOID WILL FRY A CBAZA-BASED ECU. The manual lever position switch (MLPS) also changed to accommodate an improved weather seal and the harness plug with it, as well as the order of the pins in the plug that goes to the top side of the valvebody on the outside of the trans next to the tailshaft housing.

The only disassembly I did was to remove the valvebody, remove a couple of accumulator piston springs, and open some fluid passages in the separator plate. This is called a J-mod and I will not be detailing that process here as the information is readily available to Google savvy readers. It is a type of shift kit that you can do yourself without having to buy anything but gaskets and drill bits if you don't have them already. I also had to repin some stuff, but only because I had some mismatched parts. If all your shit comes out of the same car, you'll probably be able to skip that step.

More to follow.
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SlowBox
Advanced Tuner
 
Posts: 509
Joined: Sat Jan 09, 2016 2:15 pm
Location: North Texas
Name: Troy G
Vehicle Information: 1989 Mustang GT
4r70w, 3.73
GT-40P heads
Alex's Parts springs
Stock cam
9.7:1
GT-40 upper and lower
65mm TB
Decapped injectors
Single 70mm snail
U4P0/U4P2/CBAZA
TunerPro v5
Moates QH v1.6

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