Outsmarting 4L80-E Overdrive Roller Clutch Failure

It was a harsh winter this year and many transmission rebuilders have been plagued with blown-up 4L80-E overdrive roller clutches in Chevy/GMC snow plow trucks and salt spreaders. Unfortunately, once the roller clutch starts to go, it takes a number of other parts out along with it. This includes the overrun clutch drum, as it is the inner race for the roller clutch and is part of this drum. The OD planetary is usually wiped out, as the outer race for the roller clutch is on the inner diameter of this planetary. Sometimes the planetary gears also are chipped up when pieces of the rollers are ground up in them…which means the ring gear — which is part of the forward drum — needs to be replaced as well.

The sum of these parts is a big chunk of change and hopefully the customer is paying this time. We all know the old saying, that the customer pays the first time and the shop pays the next. To help cure everyone’s winter woes — at least where the 4L80-E OD roller clutch is concerned — Sonnax offers Smart-Tech overrun clutch valve kit 34200-40K for '97-later 4L80-E and 4L85-E units. This patent-pending kit delivers exceptional protection against failure by applying the overrun clutch in all ranges other than 4th Gear, allowing the clutch to share a load the OD roller clutch otherwise struggles with on its own.

Sonnax Smart-Tech Overrun Clutch Valve Kit

Driving in the manual ranges while pushing snow will definitely help back up the roller clutch with the overrun clutch. Unfortunately for 4L80-E drivers, if they select the OD range when they are plowing, the overrun clutch can’t come on to provide better holding power. In the OD range 1^st through 3^rd Gears of a factory 4L80-E, the OD roller clutch transmits torque to the ring gear of the forward drum, through the turbine shaft, OD planetary and sun gear of the overrun clutch drum (Figure 1). When Manual 3, 2 or 1 is selected, the overrun clutch drum is applied through a passage connected by the manual valve, which provides engine braking and also backs up the roller clutch, providing a stronger connection to the OD planetary driving the forward drum (Figure 2).

Up until now, there’s been no way to get around this basic weakness of the 4L80-E transmission: the OD roller clutch in the OD range is holding by itself and the overrun clutch is only on in the manual ranges, D, 2 and 1. But what if you could, literally, get AROUND it? That’s the question Sonnax asked and how the Smart-Tech overrun clutch valve kit tackles the problem. Via an external manifold that bolts to the valve body, the Smart-Tech kit establishes a hydraulic connection to the overrun clutch as soon as the engine is started (Figure 3). With line pressure provided to the clutch, it can now be applied in ALL manual valve positions, including Reverse. The latter is a big bonus never available in the stock transmission. Think about the benefits when — for example — a driver is trying to back up a goose-neck trailer loaded down with a huge front-loader tractor. That’s an extra feature your customers will really appreciate.

With the Smart-Tech kit installed, the overrun clutch is applied in the OD position in 1^st through 3^rd Gears as well, so it is not necessary to pull the manual valve to a manual position for extra pulling power. Figure 4 shows the hydraulic function of the kit when the overrun clutch is on and when the overrun clutch is off. Note that the valve position is controlled by the presence of 4th clutch pressure; so in essence, the overrun clutch is on in every gear other than 4^th Gear. Fourth clutch pressure strokes the valve to the right and exhausts the overrun clutch. This provides a stronger connection to the forward drum through the OD planetary assembly that helps prevent OD roller clutch failure.

The next time you have a 4L80-E in the shop, build in unrivaled OD roller clutch durability and protect your warranty with the Smart-Tech overrun clutch valve kit. Components install easily onto the valve body — no transmission removal required — and will help keep your customers’ trucks working hard all season long.

Jim Dial is a Sonnax technical specialist and a member of the Sonnax TASC Force (Technical Automotive Specialties Committee), a group of recognized industry technical specialists, transmission rebuilders and Sonnax Industries Inc. technicians.