Understanding lube flow control valves in Toyota/Lexus UA/UB80 transmissions - Transmission Digest

Understanding lube flow control valves in Toyota/Lexus UA/UB80 transmissions

The Toyota/Lexus UA80 and UB80 transmissions first came out in 2017 in Highlanders and Siennas. The UA80 is used in V6 applications, and the UB80 is paired with four-cylinder versions. They have been called Toyota New Global Architecture type transmissions, and alternately referred to as the “Direct Shift 8AT” eight-speed automatic transmission. This transmission was produced to replace the previous-design U880F eight-speed and the U660/760 units to provide improved performance and efficiency.

These units are unique in several ways, and there are a couple of things that immediately stand out about this transmission. The first is the fact that the torque converter has moved away from the two-path design to a three-path design. This makes the TCC apply a separate clutch pack and piston inside of the torque converter and can provide better control when in “flex” or partial TCC apply. This new-design torque converter helps eliminate the TCC shudder issue when in partial apply—a problem that plagued the U660/760 transmissions.

The second item that makes this transmission unique is that it incorporates a new valve design. This valve is in the cooler return and lube circuits. There were no OE breakdowns of the valve body at the time Sonnax began researching the UA80 and UB80. Based solely on its function, we named it the “lube flow control valve,” or LFC valve for short. The LFC valve is in the middle valve body just below the pressure regulator valve.

At first look, the metering notches were very interesting; I have never seen something like that before. The process of reverse engineering the oil circuit uncovered the need for the metering notches and showed why they were put there. Figure 1 (above) shows a partial circuit diagram of the LFC valve and the circuits connected to it, as well as their locations in the valve body casting. Notice that the metering notches are there to provide connections to both the rear case and differential lube circuit, as well as the circuit that connects cooler return oil to the sump in most positions of the LFC valve. 

Also, notice that the LFC valve is controlled by SLT pressure. The SLT circuit is also connected to the pressure regulator valve. This is a very active circuit, as it is constantly adjusting line pressure to match engine load. A closer look at the LFC valve circuit and the different positions can be found in Figures 2 and 3. 

Figure 2 shows the LFC valve in a position during normal-to-lower line pressure. The valve is positioned more to the left, which directs cooler return oil to the rear case and differential lube circuits. It also makes a connection through the valve’s position back to the sump, which cools transmission fluid.

Tasc-Tip-December-Figure-2---Normal-to-Lower-Line-Pressure-LFCV-Position-1400
Figure 2.

During higher loads and higher line pressure, the LFC valve is positioned more to the right by higher SLT pressure. This directs cooler return oil to the rear case and differential lube circuits, but limits the connection from the cooler back to the sump (see Figure 3).

Tasc-Tip-December-Figure-3---Medium-to-High-Line-Pressure-LFCV-Position-1400
Figure 3.

In summary, this valve prioritizes lube flow to the rear case and differential most of the time and should be checked any time you are rebuilding these transmissions, especially when there is fluid overheat, drivetrain failures or unexplained clutch or brake failures.

This new-design valve has already shown signs of significant wear. The port where the SLT circuit is fed is the best location to vacuum test the valve (see Figure 4).

Tasc-Tip-December-Figure-4---LFC-Valve-in-Middle-Valve-Body-Casting-1400
Figure 4.

The complaints related to a worn bore for this valve would be: transmission fluid overheat, lube failure, planetary damage and even no line pressure rise, as the SLT circuit could be directed to the sump.

Read more stories from our TASC Force Tips series here.

Jim Dial is a Sonnax technical specialist. He is a member of the Sonnax TASC Force, a group of recognized industry technical specialists, transmission rebuilders and Sonnax technicians.

You May Also Like

The powertrain aftermarket: Growing and global

For the past few decades, the powertrain aftermarket, much like OEMs, has come to acknowledge that the marketplace for both supply sources and product sales has expanded past borders to become truly global. Various segments of our industry will have different mixes of global component supply and global sales networks. Nothing exemplified the global dependency

For the past few decades, the powertrain aftermarket, much like OEMs, has come to acknowledge that the marketplace for both supply sources and product sales has expanded past borders to become truly global. Various segments of our industry will have different mixes of global component supply and global sales networks.

6R80 whirring noise: TCC slip or engine surge?

About a month ago, we at Certified Transmission received a 2015 Ford Expedition 4WD at the shop. It was equipped with a 3.5L Turbo V6 engine and a 6R80 transmission. The complaint read, “RPMs fluctuate up and down and there is a whirring noise.” The vehicle was brought to us by one of our wholesale

The torque converter can of worms: Lockup and aftermarket programming

Lockup torque converters have been around now for some time. They came into production around the time when fuel mileage demands were put into effect by the government, and the auto manufacturers needed to do something to better connect the fluid coupling (torque converter) of the automatic transmission to the motor. By doing this, OEMs

tascfeature-1400
The Subaru mystery burn

The Subaru TR580 transmission is known for having torque converter clutch solenoid failures. An example of this can be seen in Figures 1 (above) and 2 (below). Related Articles – Allison 1000 geartrain bind-up – How to get around non-serviceable GM 6T70/75 self-tapping pump screws – Shop Profile: AAction Transmissions begins a new era by

Tech-Speak-May-Figure-1-1400
Shift Pointers: Where’s that fluid leak coming from?

A 2016 Honda CRV 2.4L (Figure 1), using a BLJA CVT 4WD transmission (Figure 2) comes in to a shop with a customer complaint of a leak. Related Articles – Watch out for high pressure in GM 8L45, 8L90 valve bodies – A part for every need: Hard parts supplier listing 2024 – Ford 8F24

Other Posts
Sonnax highlights 1350 Series three-bolt adapter flange yoke kit

Sonnax highlights its three-bolt adapter flange yoke kit for the following transmissions: 6L80, 6L90, 8L90, 10L80 units, TR6060, TR3160 manual units. It also fits 2005–2006 Pontiac GTO (differential side). Related Articles – Toledo Trans-Kit overhaul kits now available for GM 9T series – PRT adds 28 new strut assemblies – Milton Industries introduces new AirStrike

Sonnax introduces Ford 6R center support sleeve

Sonnax has introduced a hardened steel center support sleeve for Ford 6R60, 6R75 and 2009–later 6R80 transmissions. According to the company, users can restore proper hydraulic control and prevent future wear in these transmissions caused by the 3-5-R “B” clutch housing sealing rings by machining 2-6 “C” clutch housing bore (center support) and installing this

Sonnax introduces Ford 10R140 TCC signal damper piston kit

Sonnax has introduced a new drop-in TCC signal damper piston kit for Ford 10R140 transmissions. The company says users can correct circuit pressure variation in these units by replacing the worn OE damper with this kit (part no. 105740-07K). This kit includes an O-ringed sleeve and no reaming is required. Related Articles – Autel tablets

Sonnax-105740-07K-1400
Sonnax introduces oversized cooler/lube flow control valve kit

Sonnax highlights its oversized cooler/lube flow control valve kit for Toyota UA/AB transmissions. Sonnax says users can recover hydraulic control and restore cooler/lube performance in Toyota/Lexus UA80E, UA80F, UB80E, UB80F transmissions by reconditioning the bore and installing this kit (part no. 168740-08K). Related Articles – Berkeley Standard introduces JFO11E / REOFO10A remanufactured pulley set –