About a month ago there was some discussion here about putting lacquer thinner in ATF then driving aprox. 500x miles and then draining and flushing tranny. This was reccomended as a trick to clean out clogged gunked up tranny valves & passages for when tranny was not upshifting properly or going into overdrive. This was a trick to try after it was absoluteley determined that OD electric & solenoid were working 100% and it was determined that ATF fluid was at correct level and in good condition.
My '87 240 DL Sedan was not going into overdrive. I bought it used this way. Judging by poor maintenance of rest of this car I think OD probably was not working for a while. OD electric & solenoid were 100% fine. So concensus was problem was in tranny - probably clogged/gunked up. I flushed & replaced ATF. Still no good. So about a month ago I tryed the lacquer thinner in ATF Trick. I Put in 8x ounzes of lacquer thinner. Drove it for Aprox. 500x miles over past month. Drained ATF from tranny pan. Flushed out tranny/ATF(12 Quarts worth of flushing). Replaced ATF with new ATF(Not Syththetic Mobil 1 as some suggested but rather Walmart ATF). It Worked !!! Car now goes into overdrive just fine. Maybe it was just another tranny flush/ATF change that did it or maybe the lacquer thinner trick did it. I could not say but sure am happy to have a working overdrive.
Thought I would share this news/information with others who might want to try this trick but might have been hesitant until they heard & read feedback on the matter. Worked for me. Hopefully might for you too.