My Dad has an 88 grand wagoneer with an auto 727 tranny.  He just
discovered the previous owner put in ATF4 in the darn thing instead of
the Dexron.  How does one purge the fluid out (easily)?  He can of
course drop the pan, but that will probably only exchange 1/4 of the
fluid.  Is there a way to flush/purge the torque converter?

As always thank you very much.