Starting with a few four-speed automatic transmissions, increasing with the five-speeds and more so with units having six or more speeds, it is interesting to see the use of counterbalance pistons in clutch drums that drive the planetary system. Since drive-style clutches are rotational, there is a tendency for centrifugal force to creep the clutch on when it is not in use, which could cause premature damage to the frictions.
If you just read the “Technically Speaking” article in this edition of Transmission Digest you might recall that we spoke a little about how balance pistons are being used in rotational clutch drums, and their purposes. This article covers one of the problems we have seen with the C1/K1 clutch (Figure 1) as it relates to the AWF21 (Aisin TF-81SC, used in the Ford 500) and the TF60-SN (09G/K/M, used in Mini Cooper, Audi/VW) transmissions.
There have been enough different cross-connection scenarios that ATSG could easily do a full-day seminar on the subject. The worst of all involved an R4A-EL transmission in a Mazda 929 on which the input-speed sensor was cross-connected with the heated O2 sensor. Soon after the vehicle was started, voltage from the ECM that was supposed to be going to the heated O2 sensor was being routed to the TCM because of the cross-connection error.