Street Smart - July - 2017

Toyota/Lexus Adds Eight Speeds to the U881E

Each year we see manufacturers adding more gears to familiar transmissions, all in an effort to coax more miles out of each gallon of gas. In 2013, Toyota/Lexus created the U881E transaxle: the first front wheel drive, 8-speed, transverse-mounted transaxle, which began showing up in the Lexus RX350 vehicles.

Today, you’ll find this unit in BMW, GM, and Volvo vehicles. It’s a compact transaxle, and one that’s easy to work on, if you have the right information on hand.

While these units are basically identical from one manufacturer to the next, they may use different names for the components inside. Going forward, we’ll be using the Toyota/Lexus terminology; just know that the information applies to all versions of this transaxle.

First, a few details about what’s going on inside: The transaxle uses two planetary gear units to create eight forward speeds.

The rear planetary gear unit is a Ravigneaux-type gearset, which consists of:

  • Two sun gears — a middle and a rear
  • Two sets of planetary gears — long and short, with different diameters, mounted in a single planetary gearset.

Using this planetary gear set enables the transaxle to create an extremely low 1st gear range (Figure 1).

Now let’s look at the powerflow (figure 2) and function of the main components in this unit (figure 3). The C1, C2, C3, and C4 clutches each use a balance piston to control the shifts from 1st gear to 8th gear.

The shapes of the grooves in the clutches and brake linings have been optimized to reduce drag.

Pressure Testing

Before beginning a pressure test, there are a few things you’ll want to keep in mind:

Always bring the transmission fluid to normal operating temperature — 50ºC to 80ºC (122ºF to 176ºF) — before performing the pressure tests.

Turn the A/C off, and keep the pressure gauge hose away from the exhaust to prevent damage during the test.

When performing a stall test, never continue the test for more than five seconds. And, when performing multiple stall tests, always wait at least 15 seconds between tests.

Turn the auto function (shift-linked function) of the electronic parking brake system off for all pressure tests.

You’ll need to install your pressure gauge in different ports to measure the pressures in drive (figure 4) versus the pressures in reverse (figure 5).

Once you’ve performed your pressure tests, you’re ready to evaluate your results (figure 6):

If pressure is high in all ranges and tests, look for a problem in the SLT solenoid (line pressure solenoid), or the regulator valve is worn or stuck in the high position.

If pressure is low in all ranges and tests, once again you could have a problem with the SLT solenoid, or the regulator valve could be worn or stuck. In addition, check for a worn oil pump or a clogged filter.

That takes care of pressure problems that are the same across the board. But what if the pressure is only low in one range?

If the pressure is only low when you have the shift lever in drive, look for a leak in the drive range circuit, which feeds the #1 clutch (C1).

If the pressure is only low when you have the shift lever in reverse, look for a leak in the reverse circuit, which includes the #3 clutch (C3) and the #2 brake (B2).

Of course, there are a lot of places in those circuits where oil pressure can leak, but this information should put you on the right road to identifying and fixing the problem.

To learn more about what’s going on inside the U881E transaxle, make sure to reserve your place for the ATRA Powertrain Expo 2017 at the Paris Hotel and Casino in Las Vegas, October 19–22.

We’ll be covering a wealth of information on these units, including:

  • Valve Body and Check Valve Breakdown
  • Solenoid ID
  • Valve Body Bolt Location and Torque
  • Transmission Disassembly
  • Clutch Pack Clearance
  • Sprag Rotation
  • Air Checks

…and much, much more. This is one program you won’t want to miss!

And that’s not just smart, that’s street smart!