It seems that many of the newer units these days are simply an offshoot of earlier units: The 4L60 became the 4L60E; the 4T60 became the 4T60E; the 400 had an overdrive gear-set dropped in front of it, got a few solenoids and became the 4L80E.

In 1995 the 4T40E was introduced and used in some vehicles that previously used the 3T40 (125C). So, is this just an overdrive version of the 3T40? Far from it! Sure, it has the usual-solenoids, valves, planets, etc. But the geartrain is far from a simple offshoot of the 3T40.

Now that the cars with these units are of service age, it only seems fitting that it, too, be included in this "What's New" edition of GEARS. So far we've heard very few serious problems rebuilding this unit or major failures in it. So this edition of "Shop Talk" will simply be dedicated to providing some assembly and parts information.

The 4T40E uses four clutches: Reverse, Direct, Forward, and Coast; and two brakes: Intermediate and Overdrive (figure 1).

Figure 1

As far as the valve body is concerned, it looks more like one from a 4T60E than a 3T40, or an offshoot of one. It is fully computer controlled, with four solenoids: two shift solenoids, a pulse width modulated solenoid for lockup and a pressure control solenoid, also pulse width modulated (figure 2).

All of the checkballs are contained in the channel casting (figure 3). And as far as the actual valves of the valve body, they're illustrated in figure four.

Figure 2  Figure 3

Finally, solenoid firing order: One thing that has always bugged me about most domestic auto manufacturers is that they often vary the firing order of their shift solenoids to achieve the various gears. Toyota, Nissan and Honda, for example, use the same firing order for all of their units. But most domestic units, built from the same manufacturer, use a different valve operation and solenoid firing order between units. Fortunately, with only two shift solenoids, there can only be four possible combinations. GM uses three of them. The 4L60E, 4T60E and 4T65E use one; the 4L30E uses another; and the 4T40E, 4L80E and 4T80E use another. If you're like me you won't be able to keep track of them, so use the chart in figure five to monitor shift solenoid operation.

As I mentioned earlier, we haven't seen many problems with this unit, nor received many calls on it. I think we're looking at another unit that will be good for the consumer and, eventually, good for the transmission repair shops; only time will tell.

Figure 4 Figure 5