Shift Pointers
- Subject: Correct assembly and installation of overrun sprag
- Unit: 62TE
- Essential Reading: Rebuilder, Diagnostician
- Author: Wayne Colonna, ATSG, Transmission Digest Technical Editor
Those of you who read my articles know that from time to time I may bore you with gear-train operation. It’s a part of the transmission’s operation that has always fascinated me. Understanding it goes a long way toward diagnosing various complaints, especially those involving noise.
In this instance I’m going to talk about a one-way-clutch device in a 62TE transmission (figures 1 & 2).
But I first need to go through my boring explanation of the “foot bone being connected to the ankle bone” type details of the underdrive centerline shaft known as the underdrive compounder assembly (Figure 3).
The underdrive compounder assembly in the 62TE transaxle consists of a shaft driven by the transfer gears (figures 4 & 5), a stationary low-clutch drum, a rotating direct-clutch drum, a sprag and a simple planetary assembly that the compounder assembly uses to drive the pinion gear in the differential.
The design of this compounder assembly is to provide two different gear ratios, a reduction gear ratio (1.452:1) and a direct drive (1:1). When the main gearbox is in first gear (the old 41TE part of the transmission), this compounder set completes the power flow to the differential in the reduction ratio. When a shift into second takes place, only the compounder switches from a reduction ratio to the direct-drive ratio. Nothing changes in the main gearbox. A shift into third now requires the main gearbox to switch gears at the same time the compounder switches back to a reduction (see application chart in Figure 6).
If you are understanding this you would be able to guess correctly how the 3-4 shift takes place – in the compounder set as it switches from a reduction to direct-drive ratio while no change occurs in the main gearbox.
With this overview of the compounder assembly’s function, how it performs its task becomes easy to understand. It’s all about basic Planetary-Gear Rotation 101. Take a simple planetary gear set and hold the sun gear stationary; drive the ring gear and the carrier will rotate in a reduction. Drive the sun gear and the ring gear in the same direction at the same speed and the planetary locks 1:1. This is how the compounder assembly works; it takes the power flow from the main gearbox and runs it through to the differential in either a reduction or direct-drive ratio via a simple planetary gear set.
The direct-drive ratio
The main gearbox provides the input to the compounder shaft via the transfer gears at the back end of the case. This shaft then drives both the internal ring gear and the direct-clutch hub in the compounder assembly. The sun gear is snap-ringed into the direct-clutch drum (Figure 7), so when the direct clutches apply they will drive the sun gear.
Since the shaft is also driving the ring gear the planetary locks 1:1 (Figure 8).
The reduction ratio
When the direct clutch is released and the low clutch applies, both the sprag and the low clutch hold the direct-clutch drum stationary (Figure 9). Since the sun gear is attached to the direct-clutch drum, the sun gear is now held stationary. With the shaft driving the ring gear while the sun gear is being held, the carrier rotates in a reduction mode.
The sprag
Like any sprag, it needs to be installed correctly. If this sprag is installed backward, a tie-up will occur anytime the direct clutch is applied. There is an ID groove around the outside edge of the sprag’s outer race. This ID groove faces the low-clutch drum, NOT the high-clutch drum (figures 10 & 11).
If the sprag was disassembled it may be accidentally assembled incorrectly, making the identification groove useless. When the sprag is in your hand with the ID groove facing you, hold the inner race stationary. The outer race should rotate clockwise and lock counterclockwise; if it does, your one-way is assembled the right way.
Many thanks to the good folks at Alto for the use of this transmission.
