U660F Sprag Clutch

If your all-wheel-drive V6 Toyota or Lexus with the U660F six-speed pulls away weakly, flares the engine on takeoff, or acts like it is in neutral until the 1-2 shift, the one-way clutch that holds first gear is a prime suspect. This listing is a used, original-equipment Toyota one-way clutch assembly taken from a U660-family transaxle. It is described as the sprag with its outer race and thrust needle bearing, and the bearing and race surfaces spin smoothly with normal wear. It is the same part for the front-drive U660E and the all-wheel-drive U660F, because the two share the gear train.

What the sprag does in a U660F

According to ATSG's U660E technical manual, the transaxle uses two driving clutches (C1 and C2), three brakes (B1, B2 and B3), a Ravigneaux planetary set, an underdrive planetary set, and exactly one one-way clutch, labeled F1. F1 works in first gear in Drive. It locks in one direction to hold its member while the car pulls away, then freewheels as soon as the computer applies the next element for second, so the 1-2 shift happens without the timing overlap a clutch-to-clutch shift would need. Because F1 is the only sprag in the unit, a worn or broken one shows up in one place: first gear.

Symptoms of a worn U660F one-way clutch

• No movement or a slipping, high-rpm launch in first gear while Drive is selected
• A neutral feel from a stop that clears up once the transaxle shifts into second
• The car pulls normally in the lowest manual range but not in Drive
• Ratcheting or grinding noise from the transaxle when coasting to a stop
• Metal debris on the pan magnet with otherwise healthy-looking clutch material

A sprag has no sensor and no trouble code of its own. Any codes you do see in a slipping U660F are more likely to point at solenoids, the valve body or the TCM, which are the failures this family is known for.

How to confirm the sprag before you buy

Start with the fluid: Toyota specifies WS fluid, and the level can only be read correctly with the fluid between 185 and 194 F on a level vehicle, as covered in our U660E fluid type and capacity guide. A low level will cause a weak launch on its own. Next, compare Drive with manual first. In manual first a brake holds the same part of the gear train that F1 holds in Drive, so if the car pulls hard in manual first and slips in Drive, the clutches and line pressure are doing their job and the one-way clutch is not holding. If it slips in every range, look at pressure, the valve body and the forward clutch instead. Our U660E and U760E problems guide walks through those valve body and shudder checks.

Fitment

This assembly is listed for the U660F (AWD) and the U660E (FWD). The U660 family went into V6 Camry, Avalon, Venza, Highlander, Sienna, RAV4 V6 and Lexus ES 350 and RX 350 models, but some generations of those vehicles used a five-speed transaxle instead, so the model name alone does not prove fitment. Confirm the transmission code on the vehicle's ID plate or send us the year and VIN and we will check it before it ships. The U660E collection lists the other hard parts we carry for this transaxle.

Install notes

• Set rotation before it goes in. ATSG's sprag rotation chart for this unit says to hold the outer race; the inner race should freewheel counter-clockwise and lock clockwise, viewed from the rear cover end. The anti-rattle clip sits on the smallest lug.
• Inspect the mating inner race. Pitting, flat spots or a polished track means the race has to be replaced along with the sprag.
• While the case is apart, check the main gear train bearing bore. Gears Magazine reports the U660E is prone to case wear there; if the outer bearing race moves at all, the case needs repair or replacement.
• A failed sprag usually means a full teardown, so replace seals, gaskets and worn frictions at the same time with a U660F overhaul kit or a U660F master rebuild kit, and flush the cooler to remove debris.
• Refill with Toyota WS fluid only. ATSG lists the total capacity at 6.57 liters (6.94 US quarts) including the differential; a pan drop takes much less, so set the level hot at the check plug.
• Clear the transmission adaptive values with a scan tool afterward. Gears Magazine warns against trying to reset the TCM by crossing battery cables.

Is this the same sprag for the U660E and the U660F?

Yes. The listing covers both. The U660F is the all-wheel-drive version and shares the gear train, including the single F1 one-way clutch, with the front-drive U660E. Confirm your transmission code or send your year and VIN before ordering.

How do I know it is the sprag and not the clutches?

Compare Drive with manual first. If the vehicle pulls firmly in manual first but slips or will not move in first gear in Drive, the one-way clutch is not holding. Slipping in every range points to fluid level, line pressure, the valve body or the forward clutch.

Which way should the sprag rotate when installed?

Per ATSG's rotation chart for this transaxle, hold the outer race: the inner race freewheels counter-clockwise and locks clockwise when viewed from the rear cover end. Check it by hand before final assembly, because a sprag installed backward gives no first gear in Drive.

What should I replace along with it?

Replace the inner race if it is pitted, plus all seals and gaskets and any worn frictions, since the unit is fully apart. An overhaul or master rebuild kit covers the soft parts. Clean the pan, magnet and cooler so metal from the old sprag does not circulate.

What fluid does the U660F use?

Toyota WS automatic transmission fluid. Check the level only with the fluid between 185 and 194 F on a level vehicle, using the overflow check plug as described in Toyota's WS fluid level bulletin.

Is this part new?

No. It is a used original-equipment Toyota assembly. The bearing and race surfaces show normal operating wear and spin smoothly, which makes it a cost-effective option when a new sprag is unavailable or overpriced.

• Toyota/Aisin U660E and U760E: Shudder, Valve Body Wear, and the WS Fluid-Level Procedure
• U660E Fluid Type, Capacity and Service Interval
• Toyota Camry and Tacoma Transmission Service: What the Dealer Won't Tell You