Recalibrates the AX4N and 4F50N valve body to cure soft 1-2 slide when hot, falling out of 4th, and front planet burn-up from weak lube.
Ford Taurus, Mercury Sable, Lincoln Continental, Windstar and Freestar owners searching for a fix for a long, sliding 1-2 shift, a van that drops to neutral at a light, no fourth gear, or a front planetary that keeps burning up are looking at the problems this kit was designed around. This is the TransGo SK AX4N, a valve body recalibration and lube upgrade kit for the AX4N and its renamed successor, the 4F50N. It does not replace worn clutches. It changes the hydraulics that wore them out.
The AX4N is Ford's non-synchronous four-speed transaxle, an improved and different unit from the AX4S it replaced, renamed 4F50N in 2001. Its valve body sits behind the side chain cover and carries the 1-2, 2-3 and 3-4 shift valves, the main regulator, the lockup control and the accumulators that set shift feel. The SK AX4N reworks that circuit to stop runaway line pressure, which TransGo links to rough shifts and blown piston seals, and to firm up the 1-2 shift so the intermediate clutch is not slipping on every apply. The second half of the kit is lube: by re-drilling feed holes in the sprocket support and front planetary and notching the sun gear, TransGo says the unit delivers up to ten times more lube to the front planet gears on a hard pull.
A slide on the 1-2 shift can be a worn clutch, low line pressure or a sticking valve, so start with a pressure gauge; our line pressure testing guide covers the hookup. If you are not sure whether you have a flare or real slip, read our flare vs slip guide first. Heat is the other half of the story on this transaxle. TransGo found planet failures follow low coolant and a tired radiator cooler, so check the coolant level and read why transmissions overheat before you rebuild.
The kit fits the AX4N and 4F50N, not the earlier AX4S or AXOD-E, and TransGo's instructions cover 1995 through 2005 units. Common applications include the Ford Taurus and Mercury Sable, the 1995-2002 Lincoln Continental, the 2001-2003 Windstar, and the 2004 and later Freestar and Mercury Monterey. Earlier 1995-2000 Windstars used the AX4S, so check yours. The AX4N has its coast band servo in the bottom pan and a 19-bolt pan, and its data plate code is X. 2004-2005 units use a revised valve body and chain cover casting marked RF-4F, and their parts do not swap with earlier ones; the kit includes a separate instruction page for that type. For a 2006 or 2007 unit, send us your year and VIN before ordering.
The valve body work is done on the bench with TransGo's printed sheet, step by step; the sheet is the kit. The lube modifications require the transaxle to be apart, so the best time is during an overhaul. TransGo warns that valve body bolts on this unit work loose and cause comebacks, and recommends re-torquing them several times to 110 inch-pounds. They also recommend replacing the caged needle bearing at the pump with the higher-capacity AXOD bearing, Torrington B-128. If any solenoids are suspect, fit our AX4N EPC, TCC and shift solenoid kit while the cover is off. Refill with Mercon V ATF, which TransGo recommends for durability. To protect the planetary, they suggest an add-on cooler rated around 14,000 to 18,000 GVW with a low-temperature or viscosity bypass; flush the lines first, as covered in our cooler flush guide.
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No. The SK AX4N is for the AX4N and 4F50N only. The AX4S is a different transaxle despite similar dimensions. Check for the coast band servo in the bottom pan and the X code on the data plate to confirm you have an AX4N.
The valve body recalibration can be done with the valve body off, but the front planet lube upgrades require drilling the sprocket support and planetary and notching the sun gear, which means teardown. Most shops install the full kit during an overhaul.
Yes. TransGo includes a separate page for 2004-2005 units, which have the RF-4F valve body and chain cover casting. Follow that page instead of the earlier steps, because 2004-2005 parts do not interchange with earlier ones.
TransGo recommends Mercon V for durability on this unit. Check the level hot after the install and confirm it against Ford's level specification for your vehicle.
Not by itself. It corrects the pressure and lube problems that cause wear, but burned clutches or a damaged front planetary still need replacing. Fit it during the rebuild that addresses the worn parts.
