24 GEARS November/December 2006

Many, many months ago we started a series (part 1) in understanding just how

the lockup system works in Daimler-Chrysler RE units. What we explored was the concept that there are three main areas to lockup systems: electri-cal, mechanical and hydraulic. The first discussion was electrical (covered in part 1). This left us with the mechanical and hydraulic.

Here in part 2, we’ll discover the mechanical components that make up the lockup converter and just how the hydraulic system controls this locking link to engine rotation. Part 3 — bring-ing the entire system together — will be in the next issue of GEARS, as we finalize these three concepts by explor-ing the hydraulic system as the pump and valve body are involved.

Let’s look at the assembly and functions of the lockup torque con-verter. As you read through this, you’ll think: I’ve seen and heard this before. But let’s recap what you may already know. What we won’t be covering are stall speeds and vortex flow, which transmit originating torque for vehicle movement; this is just about the link for torque converter lockup.

Converter AssemblyThe torque converter is made up of

many elements. If you cut the converter open, here’s what you’ll find:

• Turbine (driven by oil flow from the stator).

• Impeller (part of the cover assembly, permanently mount-ed into the converter shell).

• Stator assembly coupled by a one-way clutch (used to cre-

ating a vortex flow of oil; redirects oil fed to it from the impeller, causing the turbine to rotate).

• Clutch disc and plate with damper springs (locks input to engine rotation; damper springs prevent breakage).

• Input hub (providing move-ment of the clutch disc).

• Pump drive hub (drives the oil pump assembly as the motor is

running).• Cover (used as the flywheel

for the clutch disc).

When converter release oil exhausts through the input shaft, the clutch disc applies, due to line pressure in the converter (turbine and impel-ler). When release oil exhausts, the input to the automatic transmission locks to engine rotation (figure 1).

Chrysler Lockup, Part 2:Chrysler Lockup, Part 2:

Dodge RE Torque Dodge RE Torque Converter:Converter: Electrical, Mechanical and HydraulicElectrical, Mechanical and Hydraulic

by Randall Schroeder

DOCTOR DOCTOR…It hurts when I shift!

Figure 1

PART 1 IS ON PAGE 18

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26 GEARS November/December 2006

This creates two benefits: 1. Fuel mileage increases2. Heat inside the transmission is

greatly reduced

For the system to work hydrauli-cally (inside the torque converter), the torque converter clutch disc assembly must be sealed to the transmission input shaft hub assembly. This sealing is done with an internal clutch hub, using a metal clad lip seal that seals the input shaft (figure 2); an O-ring, some-times accompanied by a Teflon wiper, to seal the disc assembly to the hub (figure 3); or an O-ring directly on the outer edge of the hub (figure 4) sealing the hub to the piston.

With each of these methods, the disc must be sealed to the hub. A pilot bushing in the cover keeps the clutch disc and hub centered and provides a path for clutch release oil to be present or exhausted (figure 5). This bush-ing has oil passageways on the outer diameter (figure 6) to allow release oil (converter charge) to enter the “clutch off” side of the torque converter.

Figure 3

Dodge RE Torque Converter: Electrical, Mechanical and Hydraulic

Figure 4

Figure 2

These benefits, These benefits,

especially the especially the

reduced heat, reduced heat,

greatly enhanced greatly enhanced

the durabil-the durabil-

ity of seals and ity of seals and

clutches inside clutches inside

the transmis-the transmis-

sion, which also sion, which also

extends warranty extends warranty

mileage.mileage.

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28 GEARS November/December 2006

When lockup occurs, this release oil exhausts through the bushing and input shaft, which was being sealed by the switch valve in the valve body during torque multiplication, sending it back into the sump. Not only is this bushing impor-tant for the release oil (keeping the clutch away from the cover), it’s also a major player in providing an exhaust path for the release oil to allow for lockup. If this bushing is installed incorrectly, blocking off the transfer area for oil, it will affect the operation of the converter clutch. This bushing is critical for torque converter clutch operation.

Converter Clutch SealsThe seals that allow the torque converter clutch

to lock up are not only the lip seal and O-ring for the clutch hub; the lining material of the clutch is also classified as a seal (figure 7). When damaged, it will allow line oil to leak when lock up is commanded on, and is usually followed by rear clutch failure. One of the most common cause of this is installing converter bolts that are too long, damaging the surface the con-verter clutch rides on. This is an important point to remember when rebuilding a transmission that has major burned clutches.

The mechanical aspects of the converter are important to understand, but with that out of the way, we’re ready to move on to the hydraulic system… which we’ll cover in the next issue of Doctor, Doctor. Until then, keep those transmissions in good working health.

The Doctor

Figure 6

Dodge RE Torque Converter: Electrical, Mechanical and Hydraulic

Figure 5

Figure 7

A pilot bush-A pilot bush-

ing in the cover ing in the cover

keeps the clutch keeps the clutch

disc and hub disc and hub

centered and centered and

provides a provides a

path for clutch path for clutch

release oil to release oil to

be present or be present or

exhausted.exhausted.

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