U660F Master Rebuild Kit

If your all-wheel-drive Toyota or Lexus V6 is flaring between gears, slipping on the highway or showing burnt fluid and clutch debris on the pan magnets, the transmission needs to come out and be overhauled. This master rebuild kit is built for that job on the U660F, the all-wheel-drive version of Aisin's U660 six-speed. In Toyota's naming the E suffix marks the front-wheel-drive transaxle and the F suffix marks the version that drives a rear axle as well, and this kit is cross-referenced to the U660E, so the internal soft parts are common to both.

What the master rebuild kit does in a U660F

ATSG's component chart for the U660 shows six ratios built from two rotating clutches (C1 and C2), three brakes (B1, B2 and B3) and one one-way clutch (F1). The TCM controls every apply with pulse-width-modulated linear solenoids, so it is constantly trimming pressure to keep shifts smooth as the frictions wear. Once the packs are worn past what the adaptive strategy can cover, you get flares and slips that no software reset will fix. A master kit replaces the frictions and steels in those packs and reseals the unit. The kit pictured includes friction plates, steel plates, the valve body separator gaskets, the oil pan gasket, lip seals, O-rings and sealing rings.

The all-wheel-drive version carries extra load. The same Toyota V6 torque and low first gear that Gears Magazine (ATRA) blames for case bearing-bore wear in the U660E are working through the F unit too, with the added drag of the rear driveline, so worn units often come in with several packs burned at the same time rather than just one.

Symptoms that point to a U660F overhaul

• Slipping or engine flare on upshifts, especially under load or when towing
• Delayed engagement into Drive or Reverse after the vehicle sits
• Dark, burnt-smelling fluid with fine friction material on the magnets
• Gear ratio or clutch performance codes that return after the fluid is corrected
• Leaks at more than one seal, or whine and vibration that point to bushing and centerline wear

How to confirm it before you pull the unit

Scan every module first. Gears Magazine notes that a dirty throttle body or lazy MAF sensor causes harsh coasting downshifts on these vehicles without any transmission code, and that wrong or worn-out fluid alone produces converter shudder, harsh shifts and solenoid codes. Check the fluid level hot using the overflow method in our U660E fluid type and capacity guide; Toyota's level bulletin covers the U660F the same way. A 25-50 mph shudder with good fluid is usually a converter or lockup valve problem rather than worn clutches, and our U660E and U760E problems guide walks through isolating it in Manual 3rd. If the fluid is burnt and the slip is real, the rebuild is the right call.

Fitment

This listing is for the U660F, with the U660E as its cross-reference; no specific model years are stated, so match your unit before you order. Read the identification tag on the transmission case and confirm it says U660F. The four-cylinder U760E/U760F family looks similar but is a different transmission. Clutch counts and some seals changed during production, so count plates as you disassemble, or send us your year, model and VIN and we will confirm it. All of our U660-family parts are on the U660E and U660F collection page, and the year-specific U660F master rebuild kit for 2006-2011 is there if your vehicle falls in that range.

Install notes

• Inspect drums, bushings, the pump and the case bearing bore before reassembly. If the main bearing outer race moves in the case at all, Gears says the case must be repaired or replaced.
• Soak new frictions in Toyota WS fluid and set clutch clearance on every pack.
• Service the valve body while it is out. The primary regulator, lockup control and solenoid modulator bores are known wear points, and a U660F shift kit goes in at the same time.
• Check the transfer and rear output seals separately; they are outside the main transaxle overhaul.
• Prime the pump on install, fill with Toyota WS only and set the level hot through the overflow plug.
• Clear the adaptive values with a capable scan tool (Toyota's ECT reset), not by disconnecting the battery, then drive cold to hot.

What is the difference between the U660F and the U660E?

The U660F is the all-wheel-drive version and the U660E is the front-wheel-drive transaxle. This kit is cross-referenced to the U660E, so the internal soft parts are shared, but always confirm the tag on your case reads U660F or U660E.

What is included in the kit?

As pictured: friction plates, steel plates, valve body separator gaskets, the oil pan gasket, lip seals, O-rings and sealing rings. Hard parts such as drums, bushings, the pump and the valve body are not included.

Which fluid does the U660F use after a rebuild?

Toyota Genuine ATF WS. Fill it and set the final level hot through the overflow plug, following Toyota's level-adjustment bulletin for U660E/F transmissions.

Will a rebuild kit fix a shudder at 25 to 50 mph?

Usually not. That shudder is most often the torque converter, the lockup valves in the valve body or the wrong fluid. Diagnose it in Manual 3rd first; a master kit is for slipping and burnt clutches.

Do I have to reset the TCM after installing it?

Yes. Clear the adaptive memory with a scan tool that can actually run Toyota's ECT reset, then drive the vehicle from cold to fully warm so it relearns shift pressures.

• Toyota/Aisin U660E and U760E: Shudder, Valve Body Wear, and the WS Fluid-Level Procedure
• U660E Fluid Type, Capacity and Service Interval