Shift Pointers
- Subject: Valve body and timing solenoid
- Unit: AW81-40LE
- Vehicle Application: 2004-up Chevy Aveo
- Essential Reading: Rebuilder, Diagnostician
- Author: Wayne Colonna, ATSG, Transmission Digest Technical Editor
Part 2 – the Valve Body
Picking up where we left off last month as promised, we are going to take a closer look at the valve body and the operation of the timing solenoid (see Figure 1). But before we get into it, there are a couple of things to be aware of.
Factory technical material that can be obtained for this transmission indicates that there are eight checkballs in the valve body. However, as noted in Figure 2, some models have only seven. The numbering of checkball locations is my own, and it is the #7 ball that will be missing. The associated ball seat and orifice in the spacer plate also will be absent.
The same factory information also says that there is a lockup control valve in the valve body when in some models there is not. Figures 3 through 6 provide valve location and identification.
If you look at Figure 4, the bore identified as #1 would be the location of the lockup control valve, and, of course, when it’s not there the bore will be empty.
Part 1 of this article mentioned that this transmission is in the 2004-and-newer Chevy Aveo and Aveo 5 1.6-liter vehicles. But this transmission is marketed worldwide, being used in the Daewoo Kalos and Pontiac Wave car lines as well. So there are your “some models,” notwithstanding any crossovers. So do not be alarmed when you see an empty bore and seven balls instead of eight.
Now, to the operation of the timing solenoid. This normally closed solenoid influences three valves in the valve body: a two-piece 3-4 timing valve, the 4-3 timing valve and the reverse control valve.
When a shift is made into fourth gear, the C1 (forward) clutch releases and the B1 (OD & 2nd brake) clutch applies. The timing solenoid assists in the controlled release of the C1 clutch by the way it operates the 3-4 timing valve. The solenoid remains off in all forward gears and is pulsed during the 3-4 and 4-3 shifts. Since this is a normally closed solenoid, when it is off these valves remain in the stroked position. When the solenoid is turned on, solenoid pressure is drained and the valves close by spring tension.
Figures 7 and 8 and Figure 9 provide partial hydraulics, illustrating what takes place with the timing solenoid and related valves during the 3-4 shift. You will also notice that shift solenoids 1 and 2 are off in third. The C1 clutch is fed pressure through the 3-4 shift valve. When a shift into fourth is made, shift solenoid 1 turns on and strokes the 3-4 shift valve. This opens up a passageway for C1 clutch pressure to be exhausted past the 2-3 shift valve. At the same time the 3-4 shift valve supplies pressure into the B1 clutch circuit.
When this circuit starts to pressurize, it splits the two-piece timing valve past a 0.45-inch orifice in the spacer plate. The splitting of the valve plays a role in the apply of the B1 clutch as well as the rate at which the C1 clutch is released.
When a 4-3 shift occurs, the timing solenoid is pulsed at the same time shift solenoid 2 turns off. This forces the C1 apply pressure to be briefly forced through a 0.040-inch orifice by the 4-3 timing valve for a regulated and controlled application (see Figure 10).
This timing solenoid also is used to prevent a reverse engagement should reverse be selected while the vehicle is moving forward at 5 mph or greater, as you can see in figures 11 and 12 .
Should this solenoid fail open, the vehicle will exhibit no reverse, a delayed engagement into drive and a flare on the 4-3 downshift. If it fails closed, a hard 3-4 upshift and 4-3 downshift can be expected.
